void spkezp_c ( SpiceInt targ,
SpiceDouble et,
ConstSpiceChar * ref,
ConstSpiceChar * abcorr,
SpiceInt obs,
SpiceDouble ptarg[3],
SpiceDouble * lt )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
targ I Target body NAIF ID code.
et I Observer epoch.
ref I Reference frame of output position vector.
abcorr I Aberration correction flag.
obs I Observing body NAIF ID code.
ptarg O Position of target.
lt O One way light time between observer and target.
-Detailed_Input
targ is the NAIF ID code for a target body. The target
and observer define a position vector which points
from the observer to the target.
et is the ephemeris time, expressed as seconds past
J2000 TDB, at which the position of the target body
relative to the observer is to be computed. 'et'
refers to time at the observer's location.
ref is the name of the reference frame relative to which
the output position vector should be expressed. This
may be any frame supported by the SPICE system,
including built-in frames (documented in the Frames
Required Reading) and frames defined by a loaded
frame kernel (FK).
When 'ref' designates a non-inertial frame, the
orientation of the frame is evaluated at an epoch
dependent on the selected aberration correction. See
the description of the output position vector 'ptarg'
for details.
abcorr indicates the aberration corrections to be applied to
the position of the target body to account for
one-way light time and stellar aberration. See the
discussion in the Particulars section for
recommendations on how to choose aberration
corrections.
abcorr may be any of the following:
"NONE" Apply no correction. Return the
geometric position of the target body
relative to the observer.
The following values of abcorr apply to the
"reception" case in which photons depart from the
target's location at the light-time corrected epoch
et-lt and *arrive* at the observer's location at 'et':
"LT" Correct for one-way light time (also
called "planetary aberration") using a
Newtonian formulation. This correction
yields the position of the target at
the moment it emitted photons arriving
at the observer at 'et'.
The light time correction uses an
iterative solution of the light time
equation (see Particulars for details).
The solution invoked by the "LT" option
uses one iteration.
"LT+S" Correct for one-way light time and
stellar aberration using a Newtonian
formulation. This option modifies the
position obtained with the "LT" option
to account for the observer's velocity
relative to the solar system
barycenter. The result is the apparent
position of the target---the position
as seen by the observer.
"CN" Converged Newtonian light time
correction. In solving the light time
equation, the "CN" correction iterates
until the solution converges (three
iterations on all supported platforms).
The "CN" correction typically does not
substantially improve accuracy because
the errors made by ignoring
relativistic effects may be larger than
the improvement afforded by obtaining
convergence of the light time solution.
The "CN" correction computation also
requires a significantly greater number
of CPU cycles than does the
one-iteration light time correction.
"CN+S" Converged Newtonian light time
and stellar aberration corrections.
The following values of abcorr apply to the
"transmission" case in which photons *depart* from
the observer's location at 'et' and arrive at the
target's location at the light-time corrected epoch
et+lt:
"XLT" "Transmission" case: correct for
one-way light time using a Newtonian
formulation. This correction yields the
position of the target at the moment it
receives photons emitted from the
observer's location at 'et'.
"XLT+S" "Transmission" case: correct for one-way
light time and stellar aberration using a
Newtonian formulation. This option
modifies the position obtained with the
"XLT" option to account for the observer's
velocity relative to the solar system
barycenter. The computed target position
indicates the direction that photons
emitted from the observer's location must
be "aimed" to hit the target.
"XCN" "Transmission" case: converged
Newtonian light time correction.
"XCN+S" "Transmission" case: converged
Newtonian light time and stellar
aberration corrections.
Neither special nor general relativistic effects are
accounted for in the aberration corrections applied
by this routine.
Case and blanks are not significant in the string
abcorr.
obs is the NAIF ID code for an observing body.
-Detailed_Output
ptarg is a Cartesian 3-vector representing the position of
the target body relative to the specified observer.
'ptarg' is corrected for the specified aberrations, and
is expressed with respect to the reference frame
specified by 'ref'. The three components of 'ptarg'
represent the x-, y- and z-components of the target's
position.
Units are always km.
'ptarg' points from the observer's location at 'et' to
the aberration-corrected location of the target.
Note that the sense of this position vector is
independent of the direction of radiation travel
implied by the aberration correction.
Non-inertial frames are treated as follows: letting
ltcent be the one-way light time between the observer
and the central body associated with the frame, the
orientation of the frame is evaluated at et-ltcent,
et+ltcent, or 'et' depending on whether the requested
aberration correction is, respectively, for received
radiation, transmitted radiation, or is omitted. ltcent
is computed using the method indicated by abcorr.
lt is the one-way light time between the observer and
target in seconds. If the target position is corrected
for aberrations, then 'lt' is the one-way light time
between the observer and the light time corrected
target location.
-Parameters
None.
-Exceptions
1) If name of target or observer cannot be translated to its
NAIF ID code, the error SPICE(IDCODENOTFOUND) is signaled.
2) If the reference frame 'ref' is not a recognized reference
frame the error SPICE(UNKNOWNFRAME) is signaled.
3) If the loaded kernels provide insufficient data to
compute the requested position vector, the deficiency will
be diagnosed by a routine in the call tree of this routine.
4) If an error occurs while reading an SPK or other kernel file,
the error will be diagnosed by a routine in the call tree
of this routine.
-Files
This routine computes positions using SPK files that have been
loaded into the SPICE system, normally via the kernel loading
interface routine furnsh_c. See the routine furnsh_c and the SPK
and KERNEL Required Reading for further information on loading
(and unloading) kernels.
If the output position 'ptarg' is to be expressed relative to a
non-inertial frame, or if any of the ephemeris data used to
compute 'ptarg' are expressed relative to a non-inertial frame in
the SPK files providing those data, additional kernels may be
needed to enable the reference frame transformations required to
compute the position. These additional kernels may be C-kernels, PCK
files or frame kernels. Any such kernels must already be loaded
at the time this routine is called.
-Particulars
This routine is part of the user interface to the SPICE ephemeris
system. It allows you to retrieve position information for any
ephemeris object relative to any other in a reference frame that
is convenient for further computations.
Aberration corrections
======================
In space science or engineering applications one frequently
wishes to know where to point a remote sensing instrument, such
as an optical camera or radio antenna, in order to observe or
otherwise receive radiation from a target. This pointing problem
is complicated by the finite speed of light: one needs to point
to where the target appears to be as opposed to where it actually
is at the epoch of observation. We use the adjectives
"geometric," "uncorrected," or "true" to refer to an actual
position or state of a target at a specified epoch. When a
geometric position or state vector is modified to reflect how it
appears to an observer, we describe that vector by any of the
terms "apparent," "corrected," "aberration corrected," or "light
time and stellar aberration corrected." The SPICE Toolkit can
correct for two phenomena affecting the apparent location of an
object: one-way light time (also called "planetary aberration") and
stellar aberration.
One-way light time
------------------
Correcting for one-way light time is done by computing, given an
observer and observation epoch, where a target was when the observed
photons departed the target's location. The vector from the
observer to this computed target location is called a "light time
corrected" vector. The light time correction depends on the motion
of the target relative to the solar system barycenter, but it is
independent of the velocity of the observer relative to the solar
system barycenter. Relativistic effects such as light bending and
gravitational delay are not accounted for in the light time
correction performed by this routine.
Stellar aberration
------------------
The velocity of the observer also affects the apparent location
of a target: photons arriving at the observer are subject to a
"raindrop effect" whereby their velocity relative to the observer
is, using a Newtonian approximation, the photons' velocity
relative to the solar system barycenter minus the velocity of the
observer relative to the solar system barycenter. This effect is
called "stellar aberration." Stellar aberration is independent
of the velocity of the target. The stellar aberration formula
used by this routine does not include (the much smaller)
relativistic effects.
Stellar aberration corrections are applied after light time
corrections: the light time corrected target position vector is
used as an input to the stellar aberration correction.
When light time and stellar aberration corrections are both
applied to a geometric position vector, the resulting position
vector indicates where the target "appears to be" from the
observer's location.
As opposed to computing the apparent position of a target, one
may wish to compute the pointing direction required for
transmission of photons to the target. This also requires correction
of the geometric target position for the effects of light time
and stellar aberration, but in this case the corrections are
computed for radiation traveling *from* the observer to the target.
We will refer to this situation as the "transmission" case.
The "transmission" light time correction yields the target's
location as it will be when photons emitted from the observer's
location at `et' arrive at the target. The transmission stellar
aberration correction is the inverse of the traditional stellar
aberration correction: it indicates the direction in which
radiation should be emitted so that, using a Newtonian
approximation, the sum of the velocity of the radiation relative
to the observer and of the observer's velocity, relative to the
solar system barycenter, yields a velocity vector that points in
the direction of the light time corrected position of the target.
One may object to using the term "observer" in the transmission
case, in which radiation is emitted from the observer's location.
The terminology was retained for consistency with earlier
documentation.
Below, we indicate the aberration corrections to use for some
common applications:
1) Find the apparent direction of a target. This is
the most common case for a remote-sensing observation.
Use "LT+S": apply both light time and stellar
aberration corrections.
Note that using light time corrections alone ("LT") is
generally not a good way to obtain an approximation to an
apparent target vector: since light time and stellar
aberration corrections often partially cancel each other,
it may be more accurate to use no correction at all than to
use light time alone.
2) Find the corrected pointing direction to radiate a signal
to a target. This computation is often applicable for
implementing communications sessions.
Use "XLT+S": apply both light time and stellar
aberration corrections for transmission.
3) Compute the apparent position of a target body relative
to a star or other distant object.
Use "LT" or "LT+S" as needed to match the correction
applied to the position of the distant object. For
example, if a star position is obtained from a catalog,
the position vector may not be corrected for stellar
aberration. In this case, to find the angular
separation of the star and the limb of a planet, the
vector from the observer to the planet should be
corrected for light time but not stellar aberration.
4) Obtain an uncorrected position vector derived directly from
data in an SPK file.
Use "NONE".
5) Use a geometric position vector as a low-accuracy estimate
of the apparent position for an application where execution
speed is critical.
Use "NONE".
6) While this routine cannot perform the relativistic
aberration corrections required to compute positions
with the highest possible accuracy, it can supply the
geometric positions required as inputs to these computations.
Use "NONE", then apply relativistic aberration
corrections (not available in the SPICE Toolkit).
Below, we discuss in more detail how the aberration corrections
applied by this routine are computed.
Geometric case
==============
spkezp_c begins by computing the geometric position T(et) of the
target body relative to the solar system barycenter (SSB).
Subtracting the geometric position of the observer O(et) gives
the geometric position of the target body relative to the
observer. The one-way light time, 'lt', is given by
| T(et) - O(et) |
lt = -------------------
c
The geometric relationship between the observer, target, and
solar system barycenter is as shown:
SSB ---> O(et)
| /
| /
| /
| / T(et) - O(et)
V V
T(et)
The returned position is
T(et) - O(et)
Reception case
==============
When any of the options "LT", "CN", "LT+S", "CN+S" is selected
for `abcorr', spkezp_c computes the position of the target body at
epoch et-lt, where 'lt' is the one-way light time. Let T(t) and
O(t) represent the positions of the target and observer
relative to the solar system barycenter at time t; then 'lt' is
the solution of the light-time equation
| T(et-lt) - O(et) |
lt = ------------------------ (1)
c
The ratio
| T(et) - O(et) |
--------------------- (2)
c
is used as a first approximation to 'lt'; inserting (2) into the
right hand side of the light-time equation (1) yields the
"one-iteration" estimate of the one-way light time ("LT").
Repeating the process until the estimates of 'lt' converge yields
the "converged Newtonian" light time estimate ("CN").
Subtracting the geometric position of the observer O(et) gives
the position of the target body relative to the observer:
T(et-lt) - O(et).
SSB ---> O(et)
| \ |
| \ |
| \ | T(et-lt) - O(et)
| \ |
V V V
T(et) T(et-lt)
The light time corrected position vector is
T(et-lt) - O(et)
If correction for stellar aberration is requested, the target
position is rotated toward the solar system
barycenter-relative velocity vector of the observer. The
rotation is computed as follows:
Let r be the light time corrected vector from the observer
to the object, and v be the velocity of the observer with
respect to the solar system barycenter. Let w be the angle
between them. The aberration angle phi is given by
sin(phi) = v sin(w) / c
Let h be the vector given by the cross product
h = r X v
Rotate r by phi radians about h to obtain the apparent
position of the object.
Transmission case
==================
When any of the options "XLT", "XCN", "XLT+S", "XCN+S" is
selected, spkezp_c computes the position of the target body T at
epoch et+lt, where 'lt' is the one-way light time. 'lt' is the
solution of the light-time equation
| T(et+lt) - O(et) |
lt = ------------------------ (3)
c
Subtracting the geometric position of the observer, O(et),
gives the position of the target body relative to the
observer: T(et-lt) - O(et).
SSB --> O(et)
/ | *
/ | * T(et+lt) - O(et)
/ |*
/ *|
V V V
T(et+lt) T(et)
The position component of the light-time corrected position
is the vector
T(et+lt) - O(et)
If correction for stellar aberration is requested, the target
position is rotated away from the solar system barycenter-
relative velocity vector of the observer. The rotation is
computed as in the reception case, but the sign of the
rotation angle is negated.
Precision of light time corrections
===================================
Corrections using one iteration of the light time solution
----------------------------------------------------------
When the requested aberration correction is "LT", "LT+S",
"XLT", or "XLT+S", only one iteration is performed in the
algorithm used to compute 'lt'.
The relative error in this computation
| LT_ACTUAL - LT_COMPUTED | / LT_ACTUAL
is at most
(V/C)**2
----------
1 - (V/C)
which is well approximated by (V/C)**2, where V is the
velocity of the target relative to an inertial frame and C is
the speed of light.
For nearly all objects in the solar system V is less than 60
km/sec. The value of C is 300000 km/sec. Thus the one
iteration solution for 'lt' has a potential relative error of
not more than 4*10**-8. This is a potential light time error
of approximately 2*10**-5 seconds per astronomical unit of
distance separating the observer and target. Given the bound
on V cited above:
As long as the observer and target are
separated by less than 50 astronomical units,
the error in the light time returned using
the one-iteration light time corrections
is less than 1 millisecond.
Converged corrections
---------------------
When the requested aberration correction is "CN", "CN+S",
"XCN", or "XCN+S", three iterations are performed in the
computation of 'lt'. The relative error present in this
solution is at most
(V/C)**4
----------
1 - (V/C)
which is well approximated by (V/C)**4. Mathematically the
precision of this computation is better than a nanosecond for
any pair of objects in the solar system.
However, to model the actual light time between target and
observer one must take into account effects due to general
relativity. These may be as high as a few hundredths of a
millisecond for some objects.
When one considers the extra time required to compute the
converged Newtonian light time (the state of the target relative
to the solar system barycenter is looked up three times instead
of once) together with the real gain in accuracy, it seems
unlikely that you will want to request either the "CN" or "CN+S"
light time corrections. However, these corrections can be useful
for testing situations where high precision (as opposed to
accuracy) is required.
Relativistic Corrections
=========================
This routine does not attempt to perform either general or
special relativistic corrections in computing the various
aberration corrections. For many applications relativistic
corrections are not worth the expense of added computation
cycles. If however, your application requires these additional
corrections we suggest you consult the astronomical almanac (page
B36) for a discussion of how to carry out these corrections.
-Examples
1) Load a planetary ephemeris SPK, then look up a series of
geometric positions of the moon relative to the earth,
referenced to the J2000 frame.
#include <stdio.h>
#include "SpiceUsr.h"
void main()
{
#define ABCORR "NONE"
#define FRAME "J2000"
/.
The name of the SPK file shown here is fictitious;
you must supply the name of an SPK file available
on your own computer system.
./
#define SPK "planetary_spk.bsp"
/.
ET0 represents the date 2000 Jan 1 12:00:00 TDB.
./
#define ET0 0.0
/.
Use a time step of 1 hour; look up 100 states.
./
#define STEP 3600.0
#define MAXITR 100
/.
The NAIF IDs of the earth and moon are 399 and 301 respectively.
./
#define OBSERVER 399
#define TARGET 301
/.
Local variables
./
SpiceInt i;
SpiceDouble et;
SpiceDouble lt;
SpiceDouble pos [3];
/.
Load the spk file.
./
furnsh_c ( SPK );
/.
Step through a series of epochs, looking up a position vector
at each one.
./
for ( i = 0; i < MAXITR; i++ )
{
et = ET0 + i*STEP;
spkezp_c ( TARGET, et, FRAME, ABCORR,
OBSERVER, pos, < );
printf( "\net = %20.10f\n\n", et );
printf( "J2000 x-position (km): %20.10f\n", pos[0] );
printf( "J2000 y-position (km): %20.10f\n", pos[1] );
printf( "J2000 z-position (km): %20.10f\n", pos[2] );
}
}
-Restrictions
None.
-Literature_References
SPK Required Reading.
-Author_and_Institution
C.H. Acton (JPL)
B.V. Semenov (JPL)
N.J. Bachman (JPL)
W.L. Taber (JPL)
-Version
-CSPICE Version 2.0.5, 04-APR-2008 (NJB)
Corrected minor error in description of XLT+S aberration
correction.
-CSPICE Version 2.0.4, 17-APR-2005 (NJB)
Error was corrected in example program: variable name `state'
was changed to `pos' in printf calls.
-CSPICE Version 2.0.3, 12-DEC-2004 (NJB)
Minor header error was corrected.
-CSPICE Version 2.0.2, 13-OCT-2003 (EDW)
Various minor header changes were made to improve clarity.
Added mention that 'lt' returns a value in seconds.
-CSPICE Version 2.0.1, 29-JUL-2003 (NJB) (CHA)
Various minor header changes were made to improve clarity.
-CSPICE Version 2.0.0, 31-DEC-2001 (NJB)
Updated to handle aberration corrections for transmission
of radiation. Formerly, only the reception case was
supported. The header was revised and expanded to explain
the functionality of this routine in more detail.
-CSPICE Version 1.0.0, 29-MAY-1999 (NJB) (WLT)
-Index_Entries
get target position relative to an observer
get position relative observer corrected for aberrations
read ephemeris data
read trajectory data
-&
*/
{ /* Begin spkezp_c */
/*
Participate in error tracing.
*/
chkin_c ( "spkezp_c" );
/*
Check the input strings to make sure the pointers are non-null
and the string lengths are non-zero.
*/
CHKFSTR ( CHK_STANDARD, "spkezp_c", ref );
CHKFSTR ( CHK_STANDARD, "spkezp_c", abcorr );
/*
Call the f2c'd Fortran routine. Use explicit type casts for every
type defined by f2c.
*/
spkezp_ ( ( integer * ) &targ,
( doublereal * ) &et,
( char * ) ref,
( char * ) abcorr,
( integer * ) &obs,
( doublereal * ) ptarg,
( doublereal * ) lt,
( ftnlen ) strlen(ref),
( ftnlen ) strlen(abcorr) );
chkout_c ( "spkezp_c" );
} /* End spkezp_c */
void spk14b_c ( SpiceInt handle,
ConstSpiceChar * segid,
SpiceInt body,
SpiceInt center,
ConstSpiceChar * frame,
SpiceDouble first,
SpiceDouble last,
SpiceInt chbdeg )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
handle I The handle of an SPK file open for writing.
segid I The string to use for segment identifier.
body I The NAIF ID code for the body of the segment.
center I The center of motion for body.
frame I The reference frame for this segment.
first I The first epoch for which the segment is valid.
last I The last epoch for which the segment is valid.
chbdeg I The degree of the Chebyshev Polynomial used.
-Detailed_Input
handle is the file handle of an SPK file that has been
opened for writing.
segid is the segment identifier. An SPK segment identifier
may contain up to 40 printing ASCII characters.
body is the NAIF ID for the body whose states are
to be recorded in an SPK file.
center is the NAIF ID for the center of motion associated
with body.
frame is the reference frame that states are referenced to,
for example "J2000".
first is the starting epoch, in TDB seconds past J2000, for
the ephemeris data to be placed into the segment.
last is the ending epoch, in TDB seconds past J2000, for
the ephemeris data to be placed into the segment.
chbdeg is the degree of the Chebyshev Polynomials used to
represent the ephemeris information stored in the
segment.
-Detailed_Output
None. The input data is used to create the segment summary
for the segment being started in the SPK file
associated with handle.
See the Particulars section for details about the
structure of a type 14 SPK segment.
-Parameters
None.
-Particulars
This routine begins writing a type 14 SPK segment to the open SPK
file that is associated with handle. The file must have been
opened with write access.
This routine is one of a set of three routines for creating and
adding data to type 14 SPK segments. These routines are:
spk14b_c: Begin a type 14 SPK segment. This routine must be
called before any data may be added to a type 14
segment.
spk14a_c: Add data to a type 14 SPK segment. This routine may be
called any number of times after a call to spk14b_c to
add type 14 records to the SPK segment that was
started.
spk14e_c: End a type 14 SPK segment. This routine is called to
make the type 14 segment a permanent addition to the
SPK file. Once this routine is called, no further type
14 records may be added to the segment. A new segment
must be started.
A type 14 SPK segment consists of coefficient sets for fixed order
Chebyshev polynomials over consecutive time intervals, where the
time intervals need not all be of the same length. The Chebyshev
polynomials represent the position, X, Y, and Z coordinates, and
the velocities, dX/dt, dY/dt, and dZ/dt, of body relative to
center.
The ephemeris data supplied to the type 14 SPK writer is packed
into an array as a sequence of records,
-----------------------------------------------------
| Record 1 | Record 2 | ... | Record N-1 | Record N |
-----------------------------------------------------
with each record has the following format.
------------------------------------------------
| The midpoint of the approximation interval |
------------------------------------------------
| The radius of the approximation interval |
------------------------------------------------
| chbdeg+1 coefficients for the X coordinate |
------------------------------------------------
| chbdeg+1 coefficients for the Y coordinate |
------------------------------------------------
| chbdeg+1 coefficients for the Z coordinate |
------------------------------------------------
| chbdeg+1 coefficients for the X velocity |
------------------------------------------------
| chbdeg+1 coefficients for the Y velocity |
------------------------------------------------
| chbdeg+1 coefficients for the Z velocity |
------------------------------------------------
-Examples
Assume we have the following for each of the examples that
follow.
handle is the handle of an SPK file opened with write
access.
segid is a character string of no more than 40 characters
which provides a pedigree for the data in the SPK
segment we will create.
body is the NAIF ID code for the body whose ephemeris
is to be placed into the file.
center is the center of motion for the ephemeris of body.
reffrm is the name of the SPICE reference frame for the
ephemeris.
first is the starting epoch, in seconds past J2000, for
the ephemeris data to be placed into the segment.
last is the ending epoch, in seconds past J2000, for
the ephemeris data to be placed into the segment.
Example 1:
For this example, we also assume that:
n is the number of type 14 records that we want to
put into a segment in an SPK file.
recrds contains n type 14 records packaged for the SPK
file.
etstrt contains the initial epochs for each of the
records contained in RECRDS, where
etstrt[i] < etstrt[i+1], i = 0, n-2
etstrt[1] <= first, etstrt[n-1] < last
etstrt[i+1], i = 0, n-2, is the ending epoch for
record i as well as the initial epoch for record
i+1.
Then the following code fragment demonstrates how to create a
type 14 SPK segment if all of the data for the segment is
available at one time.
#include "SpiceUsr.h"
.
.
.
#define SPK "example.bsp"
/.
If the segment is to be appended to an existing file, open
that file for "append" access. Otherwise, create a new file.
./
if ( exists_c(SPK) )
{
spkopa_c ( SPK, &handle );
}
else
{
/.
New files are supplied with an internal file name.
Comment area space may be reserved at this time; the
units are characters.
./
ifname = "Sample type 14 SPK file.";
ncomch = 1024;
spkopn_c ( SPK, ifname, ncomch, &handle );
}
/.
Begin the segment.
./
spk14b_c ( handle, segid, body, center, reffrm,
first, last, chbdeg );
/.
Add the data to the segment all at once.
./
spk14a_c ( handle, n, recrds, etstrt );
/.
End the segment, making the segment a permanent addition
to the SPK file.
./
spk14e_c ( handle );
.
.
.
/.
After all segments have been loaded, close the SPK file.
./
spkcls_c ( handle );
Example 2:
In this example we want to add type 14 SPK records, as described
above in the Particulars section, to the segments being written
as they are generated. The ability to write the records in this
way is useful if computer memory is limited. It may also be
convenient from a programming perspective to write the records
one at a time.
For this example, assume that we want to generate n type 14 SPK
records, one for each of n time intervals, writing them all to
the same segment in the SPK file. Let
n be the number of type 14 records that we want to
generate and put into a segment in an SPK file.
record be an array with enough room to hold a single type
14 record, i.e. record should have dimension at
least 6 * (chbdeg + 1 ) + 2.
start be an array of n times that are the beginning
epochs for each of the intervals of interest. The
times should be in increasing order and the start
time for the first interval should equal the
starting time for the segment.
start[i] < start[i+1], i = 0, n-2
start[0] = first
stop be an array of n times that are the ending epochs
for each of the intervals of interest. The times
should be in increasing order and the stop time for
interval i should equal the start time for interval
i+1, i.e., we want to have continuous coverage in
time across all of the records. Also, the stop time
for the last interval should equal the ending time
for the segment.
stop[i] < stop [i+1], i = 0, n-2
stop[i] = start[i+1], i = 0, n-2
stop[n-1] = last
genrec( time1, time2, record )
be a subroutine that generates a type 14 SPK record
for a time interval specified by time1 and time2.
Then the following code fragment demonstrates how to create a
type 14 SPK segment if all of the data for the segment is not
available at one time.
#include "SpiceUsr.h"
.
.
.
/.
Begin the segment.
./
spk14b_c ( handle, segid, body, center, reffrm,
first, last, chbdeg );
/.
Generate the records and write them to the segment in the
SPK file one at at time.
./
for ( i = 0; i < n; i++ )
{
genrec ( start[i], stop[i], record );
spk14a_c ( handle, 1, record, start+i );
}
/.
End the segment, making the segment a permanent addition
to the SPK file.
./
spk14e_c ( handle );
-Restrictions
The SPK file must be open with write access.
Only one segment may be written to a particular SPK file at a
time. All of the data for the segment must be written and the
segment must be ended before another segment may be started in
the file.
-Exceptions
1) If the degree of the Chebyshev Polynomial to be used for this
segment is negative, the error SPICE(INVALIDARGUMENT) will
be signaled.
2) Errors in the structure or content of the inputs other than the
degree of the Chebyshev Polynomial are diagnosed by routines
called by this one.
3) File access errors are diagnosed by routines in the call tree
of this routine.
4) If either the input frame or segment ID string pointer is null,
the error SPICE(NULLPOINTER) is signaled.
5) If either the input frame or segment ID string is empty,
the error SPICE(EMPTYSTRING) is signaled.
-Files
See handle in the Detailed_Input section.
-Author_and_Institution
N.J. Bachman (JPL)
K.R. Gehringer (JPL)
-Literature_References
None.
-Version
-CSPICE Version 1.0.1, 30-OCT-2006 (BVS)
Deleted "inertial" from the FRAME description in the Brief_I/O
section of the header.
-CSPICE Version 1.0.0, 29-JUL-1999 (NJB) (KRG)
-Index_Entries
begin writing a type_14 spk segment
-&
*/
{ /* Begin spk14b_c */
/*
Participate in error tracing.
*/
chkin_c ( "spk14b_c" );
/*
Check the input strings to make sure the pointers
are non-null and the string lengths are non-zero.
*/
CHKFSTR ( CHK_STANDARD, "spk14b_c", frame );
CHKFSTR ( CHK_STANDARD, "spk14b_c", segid );
/*
Call the f2c'd routine.
*/
spk14b_ ( ( integer * ) &handle,
( char * ) segid,
( integer * ) &body,
( integer * ) ¢er,
( char * ) frame,
( doublereal * ) &first,
( doublereal * ) &last,
( integer * ) &chbdeg,
( ftnlen ) strlen(segid),
( ftnlen ) strlen(frame) );
chkout_c ( "spk14b_c" );
} /* End spk14b_c */
void pckcov_c ( ConstSpiceChar * pck,
SpiceInt idcode,
SpiceCell * cover )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
pck I Name of PCK file.
idcode I Class ID code of PCK reference frame.
cover I/O Window giving coverage in `pck' for `idcode'.
-Detailed_Input
pck is the name of a binary PCK file.
idcode is the integer frame class ID code of a PCK reference
frame for which data are expected to exist in the
specified PCK file.
cover is an initialized CSPICE window data structure.
`cover' optionally may contain coverage data on
input; on output, the data already present in `cover'
will be combined with coverage found for the
reference frame designated by `idcode' in the file
`pck'.
If `cover' contains no data on input, its size and
cardinality still must be initialized.
-Detailed_Output
cover is a CSPICE window data structure which represents
the merged coverage for the reference frame having
frame class ID `idcode'. This is the set of time
intervals for which data for `idcode' are present in
the file `pck', merged with the set of time intervals
present in `cover' on input. The merged coverage is
represented as the union of one or more disjoint time
intervals. The window `cover' contains the pairs of
endpoints of these intervals.
The interval endpoints contained in `cover' are
ephemeris times, expressed as seconds past J2000
TDB.
See the Examples section below for a complete
example program showing how to retrieve the
endpoints from `cover'.
-Parameters
None.
-Exceptions
1) If the input file has transfer format, the error
SPICE(INVALIDFORMAT) is signaled.
2) If the input file is not a transfer file but has architecture
other than DAF, the error SPICE(BADARCHTYPE) is signaled.
3) If the input file is a binary DAF file of type other than
PCK, the error SPICE(BADFILETYPE) is signaled.
4) If the PCK file cannot be opened or read, the error will
be diagnosed by routines called by this routine. The output
window will not be modified.
5) If the size of the output window argument COVER is
insufficient to contain the actual number of intervals in the
coverage window for IDCODE, the error will be diagnosed by
routines called by this routine.
6) The error SPICE(EMPTYSTRING) is signaled if the input
string `pck' does not contain at least one character, since the
input string cannot be converted to a Fortran-style string in
this case.
7) The error SPICE(NULLPOINTER) is signaled if the input string
pointer `pck' is null.
-Files
This routine reads a PCK file.
-Particulars
This routine provides an API via which applications can determine
the coverage a specified PCK file provides for a specified
PCK class reference frame.
-Examples
1) This example demonstrates combined usage of pckcov_c and the
related PCK utility pckfrm_c.
Display the coverage for each object in a specified PCK file.
Find the set of objects in the file; for each object, find
and display the coverage.
#include <stdio.h>
#include "SpiceUsr.h"
int main()
{
/.
Local parameters
./
#define FILSIZ 256
#define MAXIV 1000
#define WINSIZ ( 2 * MAXIV )
#define TIMLEN 51
#define MAXOBJ 1000
/.
Local variables
./
SPICEDOUBLE_CELL ( cover, WINSIZ );
SPICEINT_CELL ( ids, MAXOBJ );
SpiceChar lsk [ FILSIZ ];
SpiceChar pck [ FILSIZ ];
SpiceChar timstr [ TIMLEN ];
SpiceDouble b;
SpiceDouble e;
SpiceInt i;
SpiceInt j;
SpiceInt niv;
SpiceInt obj;
/.
Load a leapseconds kernel for output time conversion.
PCKCOV itself does not require a leapseconds kernel.
./
prompt_c ( "Name of leapseconds kernel > ", FILSIZ, lsk );
furnsh_c ( lsk );
/.
Get name of PCK file.
./
prompt_c ( "Name of PCK file > ", FILSIZ, pck );
/.
Find the set of frames in the PCK file.
./
pckfrm_c ( pck, &ids );
/.
We want to display the coverage for each frame. Loop over
the contents of the ID code set, find the coverage for
each item in the set, and display the coverage.
./
for ( i = 0; i < card_c( &ids ); i++ )
{
/.
Find the coverage window for the current frame.
Empty the coverage window each time so we don't
include data for the previous frame.
./
obj = SPICE_CELL_ELEM_I( &ids, i );
scard_c ( 0, &cover );
pckcov_c ( pck, obj, &cover );
/.
Get the number of intervals in the coverage window.
./
niv = wncard_c ( &cover );
/.
Display a simple banner.
./
printf ( "%s\n", "========================================" );
printf ( "Coverage for frame %ld\n", obj );
/.
Convert the coverage interval start and stop times to TDB
calendar strings.
./
for ( j = 0; j < niv; j++ )
{
/.
Get the endpoints of the jth interval.
./
wnfetd_c ( &cover, j, &b, &e );
/.
Convert the endpoints to TDB calendar
format time strings and display them.
./
timout_c ( b,
"YYYY MON DD HR:MN:SC.### (TDB) ::TDB",
TIMLEN,
timstr );
printf ( "\n"
"Interval: %ld\n"
"Start: %s\n",
j,
timstr );
timout_c ( e,
"YYYY MON DD HR:MN:SC.### (TDB) ::TDB",
TIMLEN,
timstr );
printf ( "Stop: %s\n", timstr );
}
}
return ( 0 );
}
2) Find the coverage for the frame designated by `idcode'
provided by the set of PCK files loaded via a metakernel.
(The metakernel must also specify a leapseconds kernel.)
#include <stdio.h>
#include "SpiceUsr.h"
int main()
{
/.
Local parameters
./
#define FILSIZ 256
#define LNSIZE 81
#define MAXCOV 100000
#define WINSIZ ( 2 * MAXCOV )
#define TIMLEN 51
/.
Local variables
./
SPICEDOUBLE_CELL ( cover, WINSIZ );
SpiceBoolean found;
SpiceChar file [ FILSIZ ];
SpiceChar idch [ LNSIZE ];
SpiceChar meta [ FILSIZ ];
SpiceChar source [ FILSIZ ];
SpiceChar timstr [ TIMLEN ];
SpiceChar type [ LNSIZE ];
SpiceDouble b;
SpiceDouble e;
SpiceInt count;
SpiceInt handle;
SpiceInt i;
SpiceInt idcode;
SpiceInt niv;
/.
Prompt for the metakernel name; load the metakernel.
The metakernel lists the PCK files whose coverage
for `idcode' we'd like to determine. The metakernel
must also specify a leapseconds kernel.
./
prompt_c ( "Name of metakernel > ", FILSIZ, meta );
furnsh_c ( meta );
/.
Get the ID code of interest.
./
prompt_c ( "Enter ID code > ", LNSIZE, idch );
prsint_c ( idch, &idcode );
/.
Find out how many kernels are loaded. Loop over the
kernels: for each loaded PCK file, add its coverage
for `idcode', if any, to the coverage window.
./
ktotal_c ( "PCK", &count );
for ( i = 0; i < count; i++ )
{
kdata_c ( i, "PCK", FILSIZ, LNSIZE, FILSIZ,
file, type, source, &handle, &found );
pckcov_c ( file, idcode, &cover );
}
/.
Display results.
Get the number of intervals in the coverage window.
./
niv = wncard_c ( &cover );
/.
Display a simple banner.
./
printf ( "\nCoverage for frame %ld\n", idcode );
/.
Convert the coverage interval start and stop times to TDB
calendar strings.
./
for ( i = 0; i < niv; i++ )
{
/.
Get the endpoints of the ith interval.
./
wnfetd_c ( &cover, i, &b, &e );
/.
Convert the endpoints to TDB calendar
format time strings and display them.
./
timout_c ( b,
"YYYY MON DD HR:MN:SC.### (TDB) ::TDB",
TIMLEN,
timstr );
printf ( "\n"
"Interval: %ld\n"
"Start: %s\n",
i,
timstr );
timout_c ( e,
"YYYY MON DD HR:MN:SC.### (TDB) ::TDB",
TIMLEN,
timstr );
printf ( "Stop: %s\n", timstr );
}
return ( 0 );
}
-Restrictions
1) If an error occurs while this routine is updating the window
`cover', the window may be corrupted.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
-Version
-CSPICE Version 1.0.1, 01-JUL-2014 (NJB)
Updated index entries.
-CSPICE Version 1.0.0, 30-NOV-2007 (NJB)
-Index_Entries
get coverage window for binary pck reference frame
get coverage start and stop time for binary pck frame
-&
*/
{ /* Begin pckcov_c */
/*
Participate in error tracing.
*/
if ( return_c() )
{
return;
}
chkin_c ( "pckcov_c" );
/*
Check the input string `pck' to make sure the pointer is non-null
and the string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "pckcov_c", pck );
/*
Make sure cell data type is d.p.
*/
CELLTYPECHK ( CHK_STANDARD, "pckcov_c", SPICE_DP, cover );
/*
Initialize the cell if necessary.
*/
CELLINIT ( cover );
/*
Call the f2c'd Fortran routine.
*/
pckcov_ ( ( char * ) pck,
( integer * ) &idcode,
( doublereal * ) (cover->base),
( ftnlen ) strlen(pck) );
/*
Sync the output cell.
*/
if ( !failed_c() )
{
zzsynccl_c ( F2C, cover );
}
chkout_c ( "pckcov_c" );
} /* End pckcov_c */
void kdata_c ( SpiceInt which,
ConstSpiceChar * kind,
SpiceInt fillen,
SpiceInt typlen,
SpiceInt srclen,
SpiceChar * file,
SpiceChar * filtyp,
SpiceChar * source,
SpiceInt * handle,
SpiceBoolean * found )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
which I Index of kernel to fetch from the list of kernels.
kind I The kind of kernel to which fetches are limited.
fillen I Available space in output file string.
typlen I Available space in output kernel type string.
srclen I Available space in output source string.
file O The name of the kernel file.
filtyp O The type of the kernel.
source O Name of the source file used to load file.
handle O The handle attached to file.
found O SPICETRUE if the specified file could be located.
-Detailed_Input
which is the number of the kernel to fetch (matching the
type specified by kind) from the list of kernels that
have been loaded through the entry point furnsh_c but
that have not been unloaded through the entry point
unload_c.
The range of which is 0 to count-1, where count is
the number of kernels loaded via furnsh_c. This
count may be obtained by calling ktotal_c. See the
Examples section for an illustrative code fragment.
kind is a list of types of kernels to be considered when
fetching kernels from the list of loaded kernels. KIND
should consist of a list of words of kernels to
examine. Recognized types are
SPK --- All SPK files are counted in the total.
CK --- All CK files are counted in the total.
PCK --- All binary PCK files are counted in the
total.
EK --- All EK files are counted in the total.
TEXT --- All text kernels that are not meta-text
kernels are included in the total.
META --- All meta-text kernels are counted in the
total.
ALL --- Every type of kernel is counted in the
total.
kind is case insensitive. If a word appears in kind
that is not one of those listed above it is ignored.
See the entry point ktotal_c for examples of the use
of kind.
fillen is the amount of available space in the output file
string, including room for the terminating null.
Normally, this is the declared length of the output
string.
typlen is the amount of available space in the output kernel
type string.
srclen is the amount of available space in the output kernel
source string.
-Detailed_Output
file is the name of the file having index which in the
sequence of files of type kind currently loaded via
furnsh_c. file will be blank if there is no such kernel
is loaded.
filtyp is the type of the kernel specified by file. filtyp
will be empty if there is no file matching the
specification of which and kind.
source is the name of the source file that was used to
specify file as one to load. If file was loaded
directly via a call to furnsh_c, source will be empty.
If there is no file matching the specification of
which and kind, source will be empty.
handle is the handle attached to file if it is a binary
kernel. If file is a text kernel or meta-text kernel
handle will be zero. If there is no file matching
the specification of which and kind, handle will be
set to zero.
found is returned SPICETRUE if a file matching the
specification of which and kind exists. If there is no
such file, found will be set to SPICEFALSE.
-Parameters
None.
-Exceptions
1) If a file is not loaded matching the specification of which
and kind, found will be SPICEFALSE; file, filtyp, and source
will be empty and handle will be set to zero.
2) If any input or output character argument pointer is null, the
error SPICE(NULLPOINTER) will be signaled.
3) If any of the output string length arguments are less than 1, the
error SPICE(STRINGTOOSHORT) will be signaled.
4) If any output string has length at least 1 but is too short to
contain the output string, the corresponding is truncated on the
right. The output string is still null-terminated.
-Files
None.
-Particulars
This entry point allows you to determine which kernels have
been loaded via furnsh_c and to obtain information sufficient
to directly query those files.
-Examples
The following example shows how you could print a summary
of SPK files that have been loaded through the interface
furnsh_c.
#include <stdio.h>
#include "SpiceUsr.h"
#define FILLEN 128
#define TYPLEN 32
#define SRCLEN 128
SpiceInt which;
SpiceInt count;
SpiceInt handle;
SpiceChar file [FILLEN];
SpiceChar filtyp[TYPLEN];
SpiceChar source[SRCLEN];
SpiceBoolean found;
int main()
{
furnsh_c( "/kernels/standard.tm" );
ktotal_c ( "spk", &count );
if ( count == 0 )
{
printf ( "No SPK files loaded at this time.\n" );
}
else
{
printf ( "The loaded SPK files are: \n\n" );
}
for ( which = 0; which < count; which++ )
{
kdata_c ( which, "spk", FILLEN, TYPLEN, SRCLEN,
file, filtyp, source, &handle, &found );
printf ( "%s\n", file );
}
}
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
W.L. Taber (JPL)
-Version
-CSPICE Version 1.1.3, 02-MAY-2008 (EDW)
standard.ker renamed standard.tm
-CSPICE Version 1.1.2, 05-SEP-2007 (EDW)
Expanded Examples section to a full, compilable program.
-CSPICE Version 1.1.1, 29-DEC-2004 (LSE)
Corrected example code to match routine's argument list.
(2 arguments reversed)
-CSPICE Version 1.1.0, 02-FEB-2003 (EDW)
Corrected example code to match routine's argument list.
-CSPICE Version 1.0.0, 12-SEP-1999 (NJB) (WLT)
-Index_Entries
Retrieve information on loaded SPICE kernels
-&
*/
{ /* Begin kdata_c */
/*
Local variables
*/
logical fnd;
/*
Participate in error tracing.
*/
chkin_c ( "kdata_c" );
/*
Check the input string kind to make sure the pointer is non-null
and the string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "kdata_c", kind );
/*
Make sure the output string file has at least enough room for one
output character and a null terminator. Also check for a null
pointer.
*/
CHKOSTR ( CHK_STANDARD, "kdata_c", file, fillen );
/*
Make sure the output string filtyp has at least enough room for one
output character and a null terminator. Also check for a null
pointer.
*/
CHKOSTR ( CHK_STANDARD, "kdata_c", filtyp, typlen );
/*
Make sure the output string source has at least enough room for one
output character and a null terminator. Also check for a null
pointer.
*/
CHKOSTR ( CHK_STANDARD, "kdata_c", source, srclen );
/*
Map the input index from C to Fortran style.
*/
which++;
/*
Call the f2c'd routine.
*/
kdata_ ( ( integer * ) &which,
( char * ) kind,
( char * ) file,
( char * ) filtyp,
( char * ) source,
( integer * ) handle,
( logical * ) &fnd,
( ftnlen ) strlen(kind),
( ftnlen ) fillen-1,
( ftnlen ) typlen-1,
( ftnlen ) srclen-1 );
/*
Convert the output strings from Fortran style to C style. Set
the SpiceBoolean output found flag.
*/
F2C_ConvertStr( fillen, file );
F2C_ConvertStr( typlen, filtyp );
F2C_ConvertStr( srclen, source );
*found = fnd;
chkout_c ( "kdata_c" );
} /* End kdata_c */
void spkw02_c ( SpiceInt handle,
SpiceInt body,
SpiceInt center,
ConstSpiceChar * frame,
SpiceDouble first,
SpiceDouble last,
ConstSpiceChar * segid,
SpiceDouble intlen,
SpiceInt n,
SpiceInt polydg,
ConstSpiceDouble cdata [],
SpiceDouble btime )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
handle I Handle of an SPK file open for writing.
body I Body code for ephemeris object.
center I Body code for the center of motion of the body.
frame I The reference frame of the states.
first I First valid time for which states can be computed.
last I Last valid time for which states can be computed.
segid I Segment identifier.
intlen I Length of time covered by logical record.
n I Number of coefficient sets.
polydg I Chebyshev polynomial degree.
cdata I Array of Chebyshev coefficients.
btime I Begin time of first logical record.
-Detailed_Input
handle DAF handle of an SPK file to which a type 2 segment
is to be added. The SPK file must be open for
writing.
body NAIF integer code for an ephemeris object whose
state relative to another body is described by the
segment to be created.
center NAIF integer code for the center of motion of the
object identified by body.
frame NAIF name for a reference frame relative to which
the state information for body is specified.
first,
last Start and stop times of the time interval over
which the segment defines the state of body.
segid Segment identifier. An SPK segment identifier may
contain up to 40 characters.
intlen Length of time, in seconds, covered by each set of
Chebyshev polynomial coefficients (each logical
record). Each set of Chebyshev coefficients must
cover this fixed time interval, intlen.
n Number of sets of Chebyshev polynomial coefficients
for coordinates (number of logical records) to be
stored in the segment. There is one set of
Chebyshev coefficients for each time period.
polydg Degree of each set of Chebyshev polynomials, i.e.
the number of Chebyshev coefficients per coordinate
minus one.
cdata Array containing all the sets of Chebyshev
polynomial coefficients to be placed in the
segment of the SPK file. The coefficients are
stored in cdata in order as follows:
the (degree + 1) coefficients for the first
coordinate of the first logical record
the coefficients for the second coordinate
the coefficients for the third coordinate
the coefficients for the first coordinate for
the second logical record, ...
and so on.
btime Begin time (seconds past J2000 TDB) of first set
of Chebyshev polynomial coefficients (first
logical record). first is an appropriate value
for btime.
-Detailed_Output
None.
-Parameters
None.
-Exceptions
1) If the number of sets of coefficients is not positive
SPICE(NUMCOEFFSNOTPOS) is signalled.
2) If the interval length is not positive, SPICE(INTLENNOTPOS)
is signalled.
3) If the integer code for the reference frame is not recognized,
SPICE(INVALIDREFFRAME) is signalled.
4) If segment stop time is not greater then the begin time,
SPICE(BADDESCRTIMES) is signalled.
5) If the start time of the first record is not less than
or equal to the descriptor begin time, SPICE(BADDESCRTIMES)
is signalled.
6) If the end time of the last record is not greater than
or equal to the descriptor end time, SPICE(BADDESCRTIMES) is
signalled.
7) The error SPICE(EMPTYSTRING) is signaled if either input
string does not contain at least one character, since the
input strings cannot be converted to a Fortran-style string
in this case.
8) The error SPICE(NULLPOINTER) is signaled if either input string
pointer is null.
-Files
A new type 2 SPK segment is written to the SPK file attached
to handle.
-Particulars
This routine writes an SPK type 2 data segment to the designated
SPK file, according to the format described in the SPK Required
Reading.
Each segment can contain data for only one target, central body,
and reference frame. The Chebyshev polynomial degree and length
of time covered by each logical record are also fixed. However,
an arbitrary number of logical records of Chebyshev polynomial
coefficients can be written in each segment. Minimizing the
number of segments in an SPK file will help optimize how the SPICE
system accesses the file.
-Examples
Suppose that you have sets of Chebyshev polynomial coefficients
in an array CDATA pertaining to the position of the moon (NAIF ID
= 301), relative to the Earth-moon barycenter (NAIF ID = 3), in
the J2000 reference frame, and want to put these into a type 2
segment in an existing SPK file. The following code could be used
to add one new type 2 segment. To add multiple segments, put the
call to spkw02_c in a loop.
#include "SpiceUsr.h"
.
.
.
/.
First open the SPK file and get a handle for it.
./
spkopa_c ( spknam, &handle );
/.
Create a segment identifier.
./
segid = "MY_SAMPLE_SPK_TYPE_2_SEGMENT";
/.
Write the segment.
./
spkw02_c ( handle, 301, 3, "J2000",
first, last, segid, intlen,
n, polydg, cdata, btime );
/.
Close the file.
./
spkcls_c ( handle );
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
K.S. Zukor (JPL)
-Version
-CSPICE Version 1.0.0, 21-JUL-1999 (NJB) (KSZ)
-Index_Entries
write spk type_2 data segment
-&
*/
{ /* Begin spkw02_c */
/*
Participate in error tracing.
*/
chkin_c ( "spkw02_c" );
/*
Check the input strings to make sure the pointers
are non-null and the string lengths are non-zero.
*/
CHKFSTR ( CHK_STANDARD, "spkw02_c", frame );
CHKFSTR ( CHK_STANDARD, "spkw02_c", segid );
/*
Write the segment.
*/
spkw02_ ( ( integer * ) &handle,
( integer * ) &body,
( integer * ) ¢er,
( char * ) frame,
( doublereal * ) &first,
( doublereal * ) &last,
( char * ) segid,
( doublereal * ) &intlen,
( integer * ) &n,
( integer * ) &polydg,
( doublereal * ) cdata,
( doublereal * ) &btime,
( ftnlen ) strlen(frame),
( ftnlen ) strlen(segid) );
chkout_c ( "spkw02_c" );
} /* End spkw02_c */
void dtpool_c ( ConstSpiceChar * name,
SpiceBoolean * found,
SpiceInt * n,
SpiceChar type [1] )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
name I Name of the variable whose value is to be returned.
found O True if variable is in pool.
n O Number of values returned for name.
type O Type of the variable: 'C', 'N', or 'X'
-Detailed_Input
name is the name of the variable whose values are to be
returned.
-Detailed_Output
found is SPICETRUE if the variable is in the pool;
SPICEFALSE if it is not.
n is the number of values associated with name.
If name is not present in the pool n will be returned
with the value 0.
type is a single character indicating the type of the variable
associated with name.
'C' if the data is character data
'N' if the data is numeric.
'X' if there is no variable name in the pool.
-Parameters
None.
-Exceptions
1) If the name requested is not in the kernel pool, found
will be set to SPICEFALSE, n to zero and type to 'X'.
2) If the input string pointer is null, the error SPICE(NULLPOINTER)
will be signaled.
3) If the input string has length zero, the error SPICE(EMPTYSTRING)
will be signaled.
-Files
None.
-Particulars
This routine allows you to determine whether or not a kernel
pool variable is present and to determine its size and type
if it is.
-Examples
The following code fragment demonstrates how to determine the
properties of a stored kernel variable.
#include <stdio.h>
#include "SpiceUsr.h"
.
.
.
dtpool_c ( varnam, &found, &n, &type );
if ( found )
{
printf ( "\n"
"Properties of variable %s:\n"
"\n"
" Size: %d\n",
varnam,
n );
if ( type == 'C' )
{
printf ( " Type: Character\n" );
}
else
{
printf ( " Type: Numeric\n" );
}
}
else
{
printf ( "%s is not present in the kernel pool.\n", varnam );
}
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
W.L. Taber (JPL)
-Version
-CSPICE Version 1.1.0, 17-OCT-1999 (NJB)
Local type logical variable now used for found flag used in
interface of dtpool_.
-CSPICE Version 1.0.0, 10-MAR-1999 (NJB)
-Index_Entries
return summary information about a kernel pool variable
-&
*/
{ /* Begin dtpool_c */
/*
Local variables
*/
logical fnd;
/*
Participate in error tracing.
*/
chkin_c ( "dtpool_c" );
/*
Check the input string name to make sure the pointer is non-null
and the string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "dtpool_c", name );
/*
Call the f2c'd routine.
*/
dtpool_ ( ( char * ) name,
( logical * ) &fnd,
( integer * ) n,
( char * ) type,
( ftnlen ) strlen(name),
( ftnlen ) 1 );
/*
Assign the SpiceBoolean found flag.
*/
*found = fnd;
chkout_c ( "dtpool_c" );
} /* End dtpool_c */
void prsdp_c ( ConstSpiceChar * string,
SpiceDouble * dpval )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
string I String representing a d.p. number.
dpval O D.p. value obtained by parsing string.
-Detailed_Input
string is a string representing a double precision
number. Any string acceptable to the CSPICE
routine nparsd.c is allowed.
-Detailed_Output
dpval is the double precision number obtained by parsing
string.
-Parameters
None.
-Exceptions
1) If the input string pointer is null, the error
SPICE(NULLPOINTER) will be signaled.
2) If the input string does not contain at least one character,
the error SPICE(EMPTYSTRING) will be signaled.
3) If the input string cannot be parsed, the error
SPICE(NOTADPNUMBER) is signalled.
-Files
None.
-Particulars
The purpose of this routine is to enable safe parsing of double
precision numbers without the necessity of in-line error checking.
This routine is based on the CSPICE routine nparsd.c.
-Examples
See the routine NPARSD for an examples of allowed strings.
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
-Version
-CSPICE Version 1.1.2, 26-AUG-1999 (NJB)
Header was updated to list string exceptions.
-CSPICE Version 1.1.1, 25-MAR-1998 (EDW)
Minor corrections to header.
-CSPICE Version 1.1.0, 08-FEB-1998 (NJB)
References to C2F_CreateStr_Sig were removed; code was
cleaned up accordingly. String checks are now done using
the macro CHKFSTR.
-CSPICE Version 1.0.0, 25-OCT-1997
Based on SPICELIB Version 1.0.0, 22-JUL-1997 (NJB)
-Index_Entries
parse d.p. number with encapsulated error handling
-&
*/
{ /* Begin prsdp_c */
/*
Participate in error handling.
*/
chkin_c ( "prsdp_c");
/*
Check the input string to make sure the pointer is non-null
and the string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "prsdp_c", string );
prsdp_ ( ( char * ) string,
( doublereal * ) dpval,
( ftnlen ) strlen(string) );
chkout_c ( "prsdp_c");
} /* End prsdp_c */
void gfsubc_c ( ConstSpiceChar * target,
ConstSpiceChar * fixref,
ConstSpiceChar * method,
ConstSpiceChar * abcorr,
ConstSpiceChar * obsrvr,
ConstSpiceChar * crdsys,
ConstSpiceChar * coord,
ConstSpiceChar * relate,
SpiceDouble refval,
SpiceDouble adjust,
SpiceDouble step,
SpiceInt nintvls,
SpiceCell * cnfine,
SpiceCell * result )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
SPICE_GF_CNVTOL
P Convergence tolerance.
target I Name of the target body
fixref I Body fixed frame associated with 'target'
method I Name of method type for subpoint calculation
abcorr I Aberration correction flag
obsrvr I Name of the observing body
crdsys I Name of the coordinate system containing 'coord'
coord I Name of the coordinate of interest
relate I Operator that either looks for an extreme value
(max, min, local, absolute) or compares the
coordinate value and refval
refval I Reference value
adjust I Adjustment value for absolute extrema searches
step I Step size used for locating extrema and roots
nintvls I Workspace window interval count
cnfine I-O SPICE window to which the search is restricted
result O SPICE window containing results
-Detailed_Input
target the string name of a target body. Optionally, you may
supply the integer ID code for the object as an
integer string. For example both 'MOON' and '301'
are legitimate strings that indicate the moon is the
target body.
The target and observer define a position vector
that points from the observer to the target.
fixref the string name of the body-fixed, body-centered
reference frame associated with the target body target.
The SPICE frame subsystem must recognize the 'fixref' name.
method the string name of the method to use for the subpoint
calculation. The accepted values for method:
'Near point: ellipsoid' The sub-observer point
computation uses a
triaxial ellipsoid to
model the surface of the
target body. The
sub-observer point is
defined as the nearest
point on the target
relative to the
observer.
'Intercept: ellipsoid' The sub-observer point
computation uses a
triaxial ellipsoid to
model the surface of the
target body. The
sub-observer point is
defined as the target
surface intercept of the
line containing the
observer and the
target's center.
The method string lacks sensitivity to case, embedded, leading
and trailing blanks.
abcorr the string description of the aberration corrections to apply
to the state evaluations to account for one-way light time
and stellar aberration.
This routine accepts the same aberration corrections as does
the SPICE routine SPKEZR. See the header of SPKEZR for a
detailed description of the aberration correction options.
For convenience, the options are listed below:
'NONE' Apply no correction.
'LT' "Reception" case: correct for
one-way light time using a Newtonian
formulation.
'LT+S' "Reception" case: correct for
one-way light time and stellar
aberration using a Newtonian
formulation.
'CN' "Reception" case: converged
Newtonian light time correction.
'CN+S' "Reception" case: converged
Newtonian light time and stellar
aberration corrections.
'XLT' "Transmission" case: correct for
one-way light time using a Newtonian
formulation.
'XLT+S' "Transmission" case: correct for
one-way light time and stellar
aberration using a Newtonian
formulation.
'XCN' "Transmission" case: converged
Newtonian light time correction.
'XCN+S' "Transmission" case: converged
Newtonian light time and stellar
aberration corrections.
The abcorr string lacks sensitivity to case, and to embedded,
leading and trailing blanks.
obsrvr the string naming the observing body. Optionally, you
may supply the ID code of the object as an integer
string. For example, both 'EARTH' and '399' are
legitimate strings to supply to indicate the
observer is Earth.
crdsys the string name of the coordinate system for which the
coordinate of interest is a member.
coord the string name of the coordinate of interest in crdsys.
The supported coordinate systems and coordinate names are:
The supported coordinate systems and coordinate names are:
Coordinate System (CRDSYS) Coordinates (COORD) Range
'RECTANGULAR' 'X'
'Y'
'Z'
'LATITUDINAL' 'RADIUS'
'LONGITUDE' (-Pi,Pi]
'LATITUDE' [-Pi/2,Pi/2]
'RA/DEC' 'RANGE'
'RIGHT ASCENSION' [0,2Pi)
'DECLINATION' [-Pi/2,Pi/2]
'SPHERICAL' 'RADIUS'
'COLATITUDE' [0,Pi]
'LONGITUDE' (-Pi,Pi]
'CYLINDRICAL' 'RADIUS'
'LONGITUDE' [0,2Pi)
'Z'
'GEODETIC' 'LONGITUDE' (-Pi,Pi]
'LATITUDE' [-Pi/2,Pi/2]
'ALTITUDE'
'PLANETOGRAPHIC' 'LONGITUDE' [0,2Pi)
'LATITUDE' [-Pi/2,Pi/2]
'ALTITUDE'
The ALTITUDE coordinates have a constant value
of zero +/- roundoff for ellipsoid targets.
Limit searches for coordinate events in the GEODETIC and
PLANETOGRAPHIC coordinate systems to TARGET bodies with
axial symmetry in the equatorial plane, i.e. equality
of the body X and Y radii (oblate or prolate spheroids).
relate the string or character describing the relational operator
used to define a constraint on the selected coordinate of the
subpoint vector. The result window found by this routine
indicates the time intervals where the constraint is satisfied.
Supported values of relate and corresponding meanings are
shown below:
'>' Separation is greater than the reference
value refval.
'=' Separation is equal to the reference
value refval.
'<' Separation is less than the reference
value refval.
'ABSMAX' Separation is at an absolute maximum.
'ABSMIN' Separation is at an absolute minimum.
'LOCMAX' Separation is at a local maximum.
'LOCMIN' Separation is at a local minimum.
The caller may indicate that the region of interest
is the set of time intervals where the quantity is
within a specified measure of an absolute extremum.
The argument ADJUST (described below) is used to
specify this measure.
Local extrema are considered to exist only in the
interiors of the intervals comprising the confinement
window: a local extremum cannot exist at a boundary
point of the confinement window.
The relate string lacks sensitivity to case, leading
and trailing blanks.
refval the double precision reference value used together with
relate argument to define an equality or inequality to
satisfy by the selected coordinate of the subpoint
vector. See the discussion of relate above for
further information.
The units of refval correspond to the type as defined
by coord, radians for angular measures, kilometers for
distance measures.
adjust a double precision value used to modify searches for
absolute extrema: when 'relate' is set to ABSMAX or ABSMIN and
'adjust' is set to a positive value, gfsubc_c finds times
when the position vector coordinate is within adjust
radians/kilometers of the specified extreme value.
For 'relate' set to ABSMAX, the result window contains
time intervals when the position vector coordinate has
values between ABSMAX - adjust and ABSMAX.
For 'relate' set to ABSMIN, the result window contains
time intervals when the position vector coordinate has
values between ABSMIN and ABSMIN + adjust.
'adjust' is not used for searches for local extrema,
equality or inequality conditions.
step the double precision time step size to use in the search.
step must be short enough for a search using this step
size to locate the time intervals where coordinate function
of the subpoint vector is monotone increasing or
decreasing. However, step must not be *too* short, or
the search will take an unreasonable amount of time.
The choice of step affects the completeness but not
the precision of solutions found by this routine; the
precision is controlled by the convergence tolerance.
step has units of TDB seconds.
nintvls an integer value specifying the number of intervals in the
the internal workspace array used by this routine. 'nintvls'
should be at least as large as the number of intervals
within the search region on which the specified observer-target
vector coordinate function is monotone increasing or decreasing.
It does no harm to pick a value of 'nintvls' larger than the
minimum required to execute the specified search, but if chosen
too small, the search will fail.
cnfine a double precision SPICE window that confines the time
period over which the specified search is conducted.
cnfine may consist of a single interval or a collection
of intervals.
In some cases the confinement window can be used to
greatly reduce the time period that must be searched
for the desired solution. See the Particulars section
below for further discussion.
See the Examples section below for a code example
that shows how to create a confinement window.
-Detailed_Output
cnfine is the input confinement window, updated if necessary
so the control area of its data array indicates the
window's size and cardinality. The window data are
unchanged.
result the SPICE window of intervals, contained within the
confinement window cnfine, on which the specified
constraint is satisfied.
If result is non-empty on input, its contents
will be discarded before gfsubc_c conducts its
search.
result must be declared and initialized with sufficient
size to capture the full set of time intervals
within the search region on which the specified constraint
is satisfied.
If the search is for local extrema, or for absolute
extrema with adjust set to zero, then normally each
interval of result will be a singleton: the left and
right endpoints of each interval will be identical.
If no times within the confinement window satisfy the
constraint, result will be returned with a
cardinality of zero.
-Parameters
SPICE_GF_CNVTOL
is the convergence tolerance used for finding endpoints
of the intervals comprising the result window.
SPICE_GF_CNVTOL is used to determine when binary searches
for roots should terminate: when a root is bracketed
within an interval of length SPICE_GF_CNVTOL; the root is
considered to have been found.
The accuracy, as opposed to precision, of roots found by
this routine depends on the accuracy of the input data.
In most cases, the accuracy of solutions will be inferior
to their precision.
SPICE_GF_CNVTOL has the value 1.0e-6. Units are TDB
seconds.
-Exceptions
1) In order for this routine to produce correct results,
the step size must be appropriate for the problem at hand.
Step sizes that are too large may cause this routine to miss
roots; step sizes that are too small may cause this routine
to run unacceptably slowly and in some cases, find spurious
roots.
This routine does not diagnose invalid step sizes, except
that if the step size is non-positive, an error is signaled
by a routine in the call tree of this routine.
2) Due to numerical errors, in particular,
- Truncation error in time values
- Finite tolerance value
- Errors in computed geometric quantities
it is *normal* for the condition of interest to not always be
satisfied near the endpoints of the intervals comprising the
result window.
The result window may need to be contracted slightly by the
caller to achieve desired results. The SPICE window routine
wncond_c can be used to contract the result window.
3) If an error (typically cell overflow) occurs while performing
window arithmetic, the error will be diagnosed by a routine
in the call tree of this routine.
4) If the relational operator `relate' is not recognized, an
error is signaled by a routine in the call tree of this
routine.
5) If the aberration correction specifier contains an
unrecognized value, an error is signaled by a routine in the
call tree of this routine.
6) If `adjust' is negative, an error is signaled by a routine in
the call tree of this routine.
7) If either of the input body names do not map to NAIF ID
codes, an error is signaled by a routine in the call tree of
this routine.
8) If required ephemerides or other kernel data are not
available, an error is signaled by a routine in the call tree
of this routine.
9) If any input string argument pointer is null, the error
SPICE(NULLPOINTER) will be signaled.
10) If any input string argument is empty, the error
SPICE(EMPTYSTRING) will be signaled.
11) If the workspace interval count 'nintvls' is less than 1, the
error SPICE(VALUEOUTOFRANGE) will be signaled.
12) If the required amount of workspace memory cannot be
allocated, the error SPICE(MALLOCFAILURE) will be
signaled.
-Files
Appropriate SPK and PCK kernels must be loaded by the
calling program before this routine is called.
The following data are required:
- SPK data: the calling application must load ephemeris data
for the targets, observer, and any intermediate objects in
a chain connecting the targets and observer that cover the time
period specified by the window CNFINE. If aberration
corrections are used, the states of target and observer
relative to the solar system barycenter must be calculable
from the available ephemeris data. Typically ephemeris data
are made available by loading one or more SPK files using
FURNSH.
- PCK data: bodies modeled as triaxial ellipsoids must have
semi-axis lengths provided by variables in the kernel pool.
Typically these data are made available by loading a text
PCK file using FURNSH.
- If non-inertial reference frames are used, then PCK
files, frame kernels, C-kernels, and SCLK kernels may be
needed.
Such kernel data are normally loaded once per program
run, NOT every time this routine is called.
-Particulars
This routine provides a simpler, but less flexible interface
than does the routine gfevnt_c for conducting searches for
subpoint position vector coordinate value events.
Applications that require support for progress reporting, interrupt
handling, non-default step or refinement functions, or non-default
convergence tolerance should call gfevnt_c rather than this routine.
This routine determines a set of one or more time intervals
within the confinement window when the selected coordinate of
the subpoint position vector satisfies a caller-specified
constraint. The resulting set of intervals is returned as a SPICE
window.
Below we discuss in greater detail aspects of this routine's
solution process that are relevant to correct and efficient
use of this routine in user applications.
The Search Process
==================
Regardless of the type of constraint selected by the caller, this
routine starts the search for solutions by determining the time
periods, within the confinement window, over which the specified
coordinate function is monotone increasing and monotone
decreasing. Each of these time periods is represented by a SPICE
window. Having found these windows, all of the coordinate
function's local extrema within the confinement window are known.
Absolute extrema then can be found very easily.
Within any interval of these "monotone" windows, there will be at
most one solution of any equality constraint. Since the boundary
of the solution set for any inequality constraint is the set
of points where an equality constraint is met, the solutions of
both equality and inequality constraints can be found easily
once the monotone windows have been found.
Step Size
=========
The monotone windows (described above) are found using a two-step
search process. Each interval of the confinement window is
searched as follows: first, the input step size is used to
determine the time separation at which the sign of the rate of
change of coordinate will be sampled. Starting at
the left endpoint of an interval, samples will be taken at each
step. If a change of sign is found, a root has been bracketed; at
that point, the time at which the time derivative of the coordinate
is zero can be found by a refinement process, for example,
using a binary search.
Note that the optimal choice of step size depends on the lengths
of the intervals over which the coordinate function is monotone:
the step size should be shorter than the shortest of these
intervals (within the confinement window).
The optimal step size is *not* necessarily related to the lengths
of the intervals comprising the result window. For example, if
the shortest monotone interval has length 10 days, and if the
shortest result window interval has length 5 minutes, a step size
of 9.9 days is still adequate to find all of the intervals in the
result window. In situations like this, the technique of using
monotone windows yields a dramatic efficiency improvement over a
state-based search that simply tests at each step whether the
specified constraint is satisfied. The latter type of search can
miss solution intervals if the step size is shorter than the
shortest solution interval.
Having some knowledge of the relative geometry of the target and
observer can be a valuable aid in picking a reasonable step size.
In general, the user can compensate for lack of such knowledge by
picking a very short step size; the cost is increased computation
time.
Note that the step size is not related to the precision with which
the endpoints of the intervals of the result window are computed.
That precision level is controlled by the convergence tolerance.
Convergence Tolerance
=====================
As described above, the root-finding process used by this routine
involves first bracketing roots and then using a search process
to locate them. "Roots" are both times when local extrema are
attained and times when the distance function is equal to a
reference value. All endpoints of the intervals comprising the
result window are either endpoints of intervals of the
confinement window or roots.
Once a root has been bracketed, a refinement process is used to
narrow down the time interval within which the root must lie.
This refinement process terminates when the location of the root
has been determined to within an error margin called the
"convergence tolerance." The convergence tolerance used by this
routine is set by the parameter SPICE_GF_CNVTOL.
The value of SPICE_GF_CNVTOL is set to a "tight" value in the f2c'd
routine so that the tolerance doesn't become the limiting factor
in the accuracy of solutions found by this routine. In general the
accuracy of input data will be the limiting factor.
To use a different tolerance value, a lower-level GF routine such
as gfevnt_c must be called. Making the tolerance tighter than
SPICE_GF_CNVTOL is unlikely to be useful, since the results are unlikely
to be more accurate. Making the tolerance looser will speed up
searches somewhat, since a few convergence steps will be omitted.
However, in most cases, the step size is likely to have a much
greater effect on processing time than would the convergence
tolerance.
The Confinement Window
======================
The simplest use of the confinement window is to specify a time
interval within which a solution is sought. However, the
confinement window can, in some cases, be used to make searches
more efficient. Sometimes it's possible to do an efficient search
to reduce the size of the time period over which a relatively
slow search of interest must be performed.
Practical use of the coordinate search capability would likely
consist of searches over multiple coordinate constraints to find
time intervals that satisfies the constraints. An effective
technique to accomplish such a search is to use the result
window from one search as the confinement window of the next.
Longitude and Right Ascension
=============================
The cyclic nature of the longitude and right ascension coordinates
produces branch cuts at +/- 180 degrees longitude and 0-360
longitude. Round-off error may cause solutions near these branches
to cross the branch. Use of the SPICE routine wncond_c will contract
solution windows by some epsilon, reducing the measure of the
windows and eliminating the branch crossing. A one millisecond
contraction will in most cases eliminate numerical round-off caused
branch crossings.
-Examples
The numerical results shown for these examples may differ across
platforms. The results depend on the SPICE kernels used as
input, the compiler and supporting libraries, and the machine
specific arithmetic implementation.
The example shown below requires a "standard" set of SPICE
kernels. We list these kernels in a meta kernel named 'standard.tm'.
KPL/MK
This meta-kernel is intended to support operation of SPICE
example programs. The kernels shown here should not be
assumed to contain adequate or correct versions of data
required by SPICE-based user applications.
In order for an application to use this meta-kernel, the
kernels referenced here must be present in the user's
current working directory.
The names and contents of the kernels referenced
by this meta-kernel are as follows:
File name Contents
--------- --------
de414.bsp Planetary ephemeris
pck00008.tpc Planet orientation and
radii
naif0008.tls Leapseconds
\begindata
KERNELS_TO_LOAD = ( '/kernels/gen/lsk/naif0008.tls'
'/kernels/gen/spk/de414.bsp'
'/kernels/gen/pck/pck00008.tpc'
)
Example:
Find the time during 2007 for which the subpoint position vector
of the sun on earth in the IAU_EARTH frame lies within a geodetic
latitude-longitude "box" defined as
16 degrees <= latitude <= 17 degrees
85 degrees <= longitude <= 86 degrees
This problem requires four searches, each search on one of the
box restrictions. The user needs also realize the temporal
behavior of latitude greatly differs from that of the longitude. The
sub-observer point latitude varies between approximately 23.44 degrees
and -23.44 degrees during the year. The sub-observer point longitude
varies between -180 degrees and 180 degrees in one day.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "SpiceUsr.h"
#define MAXWIN 100
#define TIMFMT "YYYY-MON-DD HR:MN:SC.###### (TDB) ::TDB ::RND"
#define STRLEN 64
int main( int argc, char **argv )
{
/.
Create the needed windows. Note, one window
consists of two values, so the total number
of cell values to allocate equals twice
the number of intervals.
./
SPICEDOUBLE_CELL ( result1, 2*MAXWIN );
SPICEDOUBLE_CELL ( result2, 2*MAXWIN );
SPICEDOUBLE_CELL ( result3, 2*MAXWIN );
SPICEDOUBLE_CELL ( result4, 2*MAXWIN );
SPICEDOUBLE_CELL ( cnfine, 2 );
SpiceDouble begtim;
SpiceDouble endtim;
SpiceDouble step;
SpiceDouble adjust;
SpiceDouble refval;
SpiceDouble beg;
SpiceDouble end;
SpiceChar begstr [ STRLEN ];
SpiceChar endstr [ STRLEN ];
SpiceChar * target = "EARTH";
SpiceChar * obsrvr = "SUN";
SpiceChar * fixref = "IAU_EARTH";
SpiceChar * method = "Near point: ellipsoid";
SpiceChar * crdsys = "GEODETIC";
SpiceChar * abcorr = "NONE";
SpiceInt count;
SpiceInt i;
/.
Load kernels.
./
furnsh_c( "standard.tm" );
/.
Store the time bounds of our search interval in
the cnfine confinement window.
./
str2et_c( "2007 JAN 01", &begtim );
str2et_c( "2008 JAN 01", &endtim );
wninsd_c ( begtim, endtim, &cnfine );
/.
Perform four searches to determine the times when the
latitude-longitude box restriction conditions apply to
the subpoint vector.
Perform the searches such that the result window of a search
serves as the confinement window of the subsequent search.
Since the latitude coordinate varies slowly and is well behaved
over the time of the confinement window, search first for the
windows satisfying the latitude requirements, then use that result
as confinement for the longitude search.
./
/.
The latitude varies relatively slowly, ~46 degrees during the
year. The extrema occur approximately every six months.
Search using a step size less than half that value (180 days).
For this example use ninety days (in units of seconds).
./
step = (90.)*spd_c();
adjust = 0.;
{
SpiceChar * coord = "LATITUDE";
SpiceChar * relate = ">";
refval = 16. *rpd_c();
gfsubc_c ( target, fixref,
method, abcorr, obsrvr,
crdsys, coord,
relate, refval,
adjust, step,
MAXWIN,
&cnfine, &result1 );
}
{
SpiceChar * coord = "LATITUDE";
SpiceChar * relate = "<";
refval = 17. *rpd_c();
gfsubc_c ( target, fixref,
method, abcorr, obsrvr,
crdsys, coord,
relate, refval,
adjust, step,
MAXWIN,
&result1, &result2 );
}
/.
Now the longitude search.
./
/.
Reset the stepsize to something appropriate for the 360
degrees in 24 hours domain. The longitude shows near
linear behavior so use a stepsize less than half the period
of twelve hours. Ten hours will suffice in this case.
./
step = (10./24.)*spd_c();
{
SpiceChar * coord = "LONGITUDE";
SpiceChar * relate = ">";
refval = 85. *rpd_c();
gfsubc_c ( target, fixref,
method, abcorr, obsrvr,
crdsys, coord,
relate, refval,
adjust, step,
MAXWIN,
&result2, &result3 );
/.
Contract the endpoints of each window to account
for possible round-off error at the -180/180 degree branch.
A contraction value of a millisecond should eliminate
any round-off caused branch crossing.
./
wncond_c( 1e-3, 1e-3, &result3 );
}
{
SpiceChar * coord = "LONGITUDE";
SpiceChar * relate = "<";
refval = 86. *rpd_c();
gfsubc_c ( target, fixref,
method, abcorr, obsrvr,
crdsys, coord,
relate, refval,
adjust, step,
MAXWIN,
&result3, &result4 );
}
/.
List the beginning and ending points in each interval
if result contains data.
./
count = wncard_c( &result4 );
/.
Display the results.
./
if (count == 0 )
{
printf ( "Result window is empty.\n\n" );
}
else
{
for ( i = 0; i < count; i++ )
{
/.
Fetch the endpoints of the Ith interval
of the result window.
./
wnfetd_c ( &result4, i, &beg, &end );
timout_c ( beg, TIMFMT, STRLEN, begstr );
timout_c ( end, TIMFMT, STRLEN, endstr );
printf ( "Interval %d\n", i + 1);
printf ( "Beginning TDB %s \n", begstr );
printf ( "Ending TDB %s \n\n", endstr );
}
}
kclear_c();
return( 0 );
}
The program outputs:
Interval 1
Beginning TDB 2007-MAY-05 06:14:04.637735 (TDB)
Ending TDB 2007-MAY-05 06:18:04.621908 (TDB)
Interval 2
Beginning TDB 2007-MAY-06 06:13:59.583483 (TDB)
Ending TDB 2007-MAY-06 06:17:59.569239 (TDB)
Interval 3
Beginning TDB 2007-MAY-07 06:13:55.102939 (TDB)
Ending TDB 2007-MAY-07 06:17:55.090299 (TDB)
Interval 4
Beginning TDB 2007-MAY-08 06:13:51.202604 (TDB)
Ending TDB 2007-MAY-08 06:17:51.191583 (TDB)
Interval 5
Beginning TDB 2007-AUG-06 06:23:17.282927 (TDB)
Ending TDB 2007-AUG-06 06:27:17.264009 (TDB)
Interval 6
Beginning TDB 2007-AUG-07 06:23:10.545441 (TDB)
Ending TDB 2007-AUG-07 06:27:10.524926 (TDB)
Interval 7
Beginning TDB 2007-AUG-08 06:23:03.233996 (TDB)
Ending TDB 2007-AUG-08 06:27:03.211889 (TDB)
-Restrictions
1) The kernel files to be used by this routine must be loaded
(normally via the CSPICE routine furnsh_c) before this routine
is called.
2) This routine has the side effect of re-initializing the
coordinate quantity utility package. Callers may
need to re-initialize the package after calling this routine.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
E.D. Wright (JPL)
-Version
-CSPICE Version 1.0.1, 26-AUG-2009, EDW (JPL)
Edit to Example description, replaced "intercept" with
"sub-observer point."
Correction of several typos.
-CSPICE Version 1.0.0, 10-FEB-2009 (NJB) (EDW)
-Index_Entries
GF subpoint coordinate search
-&
*/
{ /* Begin gfsubc_c */
/*
Local variables
*/
doublereal * work;
SpiceInt nBytes;
static SpiceInt nw = SPICE_GF_NWMAX;
/*
Participate in error tracing.
*/
if ( return_c() )
{
return;
}
chkin_c ( "gfsubc_c" );
/*
Make sure cell data types are d.p.
*/
CELLTYPECHK2 ( CHK_STANDARD, "gfsubc_c", SPICE_DP, cnfine, result );
/*
Initialize the input cells if necessary.
*/
CELLINIT2 ( cnfine, result );
/*
Check the input strings to make sure each pointer is non-null
and each string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "gfsubc_c", target );
CHKFSTR ( CHK_STANDARD, "gfsubc_c", fixref );
CHKFSTR ( CHK_STANDARD, "gfsubc_c", method );
CHKFSTR ( CHK_STANDARD, "gfsubc_c", abcorr );
CHKFSTR ( CHK_STANDARD, "gfsubc_c", obsrvr );
CHKFSTR ( CHK_STANDARD, "gfsubc_c", crdsys );
CHKFSTR ( CHK_STANDARD, "gfsubc_c", coord );
CHKFSTR ( CHK_STANDARD, "gfsubc_c", relate );
/*
Check the workspace size; some mallocs have a violent
dislike for negative allocation amounts. To be safe,
rule out a count of zero intervals as well.
*/
if ( nintvls < 1 )
{
setmsg_c ( "The specified workspace interval count # was "
"less than the minimum allowed value of one (1)." );
errint_c ( "#", nintvls );
sigerr_c ( "SPICE(VALUEOUTOFRANGE)" );
chkout_c ( "gfposc_c" );
return;
}
/*
Allocate the workspace. 'nintvls' indicates the maximum number of
intervals returned in 'result'. An interval consists of
two values.
*/
nintvls = 2 * nintvls;
nBytes = ( nintvls + SPICE_CELL_CTRLSZ ) * nw * sizeof(SpiceDouble);
work = (doublereal *) alloc_SpiceMemory( nBytes );
if ( !work )
{
setmsg_c ( "Workspace allocation of # bytes failed due to "
"malloc failure" );
errint_c ( "#", nBytes );
sigerr_c ( "SPICE(MALLOCFAILED)" );
chkout_c ( "gfsubc_c" );
return;
}
/*
Let the f2'd routine do the work.
*/
gfsubc_ ( ( char * ) target,
( char * ) fixref,
( char * ) method,
( char * ) abcorr,
( char * ) obsrvr,
( char * ) crdsys,
( char * ) coord,
( char * ) relate,
( doublereal * ) &refval,
( doublereal * ) &adjust,
( doublereal * ) &step,
( doublereal * ) (cnfine->base),
( integer * ) &nintvls,
( integer * ) &nw,
( doublereal * ) work,
( doublereal * ) (result->base),
( ftnlen ) strlen(target),
( ftnlen ) strlen(fixref),
( ftnlen ) strlen(method),
( ftnlen ) strlen(abcorr),
( ftnlen ) strlen(obsrvr),
( ftnlen ) strlen(crdsys),
( ftnlen ) strlen(coord),
( ftnlen ) strlen(relate) );
/*
De-allocate the workspace.
*/
free_SpiceMemory( work );
/*
Sync the output cell.
*/
if ( !failed_c() )
{
zzsynccl_c ( F2C, result ) ;
}
ALLOC_CHECK;
chkout_c ( "gfsubc_c" );
} /* End gfsubc_c */
void sxform_c ( ConstSpiceChar * from,
ConstSpiceChar * to,
SpiceDouble et,
SpiceDouble xform[6][6] )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
from I Name of the frame to transform from.
to I Name of the frame to transform to.
et I Epoch of the state transformation matrix.
xform O A state transformation matrix.
-Detailed_Input
from is the name of a reference frame in which a state is
known.
to is the name of a reference frame in which it is desired
to represent the state.
et is the epoch in ephemeris seconds past the epoch of
J2000 (TDB) at which the state transformation matrix
should be evaluated.
-Detailed_Output
xform is the matrix that transforms states from the reference
frame `from' to the frame `to' at epoch `et'. If (x, y,
z, dx, dy, dz) is a state relative to the frame `from'
then the vector ( x', y', z', dx', dy', dz' ) is the
same state relative to the frame `to' at epoch `et'.
Here the vector ( x', y', z', dx', dy', dz' ) is defined
by the equation:
- - - - - -
| x' | | | | x |
| y' | | | | y |
| z' | = | xform | | z |
| dx' | | | | dx |
| dy' | | | | dy |
| dz' | | | | dz |
- - - - - -
-Parameters
None.
-Exceptions
1) If sufficient information has not been supplied via loaded
SPICE kernels to compute the transformation between the
two frames, the error will be diagnosed by a routine
in the call tree of this routine.
2) If either frame `from' or `to' is not recognized the error
SPICE(UNKNOWNFRAME) will be signaled.
-Files
None.
-Particulars
This routine provides the user level interface for computing
state transformations from one reference frame to another.
Note that the reference frames may be inertial or non-inertial.
However, the user must take care that sufficient SPICE kernel
information is loaded to provide a complete state transformation
path from the `from' frame to the `to' frame.
-Examples
Suppose that you have geodetic coordinates of a station on
the surface of the earth and that you need the inertial
(J2000) state of this station. The following code fragment
illustrates how to transform the position of the station to
a J2000 state.
#include "SpiceUsr.h"
.
.
.
bodvcd_c ( 399, radii, 3, &n, abc );
equatr = abc[0];
polar = abc[2];
f = (equatr - polar) / equatr;
georec_c ( long, lat, 0.0, equatr, f, estate );
estate[3] = 0.0;
estate[4] = 0.0;
estate[5] = 0.0;
sxform_c ( "IAU_EARTH", "J2000", et, xform );
mxvg_c ( xform, estate, 6, 6, jstate );
The state `jstate' is the desired J2000 state of the station.
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
C.H. Acton (JPL)
N.J. Bachman (JPL)
B.V. Semenov (JPL)
W.L. Taber (JPL)
-Version
-CSPICE Version 1.1.3, 27-FEB-2008 (BVS)
Added FRAMES to the Required_Reading section of the header.
-CSPICE Version 1.1.2, 24-OCT-2005 (NJB)
Header updates: example had invalid flattening factor
computation; this was corrected. Reference to bodvar_c was
replaced with reference to bodvcd_c.
-CSPICE Version 1.1.1, 03-JUL-2003 (NJB) (CHA)
Various header corrections were made.
-CSPICE Version 1.1.0, 08-FEB-1998 (NJB)
References to C2F_CreateStr_Sig were removed; code was
cleaned up accordingly. String checks are now done using
the macro CHKFSTR.
-CSPICE Version 1.0.0, 25-OCT-1997 (NJB)
Based on SPICELIB Version 1.0.0, 19-SEP-1995 (WLT)
-Index_Entries
Find a state transformation matrix
-&
*/
{ /* Begin sxform_c */
/*
Participate in error tracing.
*/
chkin_c ( "sxform_c");
/*
Check the input strings to make sure the pointers are non-null
and the string lengths are non-zero.
*/
CHKFSTR ( CHK_STANDARD, "sxform_c", from );
CHKFSTR ( CHK_STANDARD, "sxform_c", to );
/*
Get the desired matrix from sxform_.
*/
sxform_ ( ( char * ) from,
( char * ) to,
( doublereal * ) &et,
( doublereal * ) xform,
( ftnlen ) strlen(from),
( ftnlen ) strlen(to) );
/*
Transpose the matrix on output.
*/
xpose6_c ( xform, xform );
chkout_c ( "sxform_c");
} /* End sxform_c */
void gfoclt_c ( ConstSpiceChar * occtyp,
ConstSpiceChar * front,
ConstSpiceChar * fshape,
ConstSpiceChar * fframe,
ConstSpiceChar * back,
ConstSpiceChar * bshape,
ConstSpiceChar * bframe,
ConstSpiceChar * abcorr,
ConstSpiceChar * obsrvr,
SpiceDouble step,
SpiceCell * cnfine,
SpiceCell * result )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
--------------- --- -------------------------------------------------
SPICE_GF_CNVTOL P Convergence tolerance.
occtyp I Type of occultation.
front I Name of body occulting the other.
fshape I Type of shape model used for front body.
fframe I Body-fixed, body-centered frame for front body.
back I Name of body occulted by the other.
bshape I Type of shape model used for back body.
bframe I Body-fixed, body-centered frame for back body.
abcorr I Aberration correction flag.
obsrvr I Name of the observing body.
step I Step size in seconds for finding occultation
events.
cnfine I-O SPICE window to which the search is restricted.
result O SPICE window containing results.
-Detailed_Input
occtyp indicates the type of occultation that is to be found.
Note that transits are considered to be a type of
occultation.
Supported values and corresponding definitions are:
"FULL" denotes the full occultation
of the body designated by
`back' by the body designated
by `front', as seen from
the location of the observer.
In other words, the occulted
body is completely invisible
as seen from the observer's
location.
"ANNULAR" denotes an annular
occultation: the body
designated by `front' blocks
part of, but not the limb of,
the body designated by `back',
as seen from the location of
the observer.
"PARTIAL" denotes a partial, non-annular
occultation: the body designated
by `front' blocks part, but not
all, of the limb of the body
designated by `back', as seen
from the location of the
observer.
"ANY" denotes any of the above three
types of occultations:
"PARTIAL", "ANNULAR", or
"FULL".
"ANY" should be used to search
for times when the body
designated by `front' blocks
any part of the body designated
by `back'.
The option "ANY" must be used
if either the front or back
target body is modeled as
a point.
Case and leading or trailing blanks are not
significant in the string `occtyp'.
front is the name of the target body that occults---that is,
passes in front of---the other. Optionally, you may
supply the integer NAIF ID code for the body as a
string. For example both "MOON" and "301" are
legitimate strings that designate the Moon.
Case and leading or trailing blanks are not
significant in the string `front'.
fshape is a string indicating the geometric model used to
represent the shape of the front target body. The
supported options are:
"ELLIPSOID" Use a triaxial ellipsoid model
with radius values provided via the
kernel pool. A kernel variable
having a name of the form
"BODYnnn_RADII"
where nnn represents the NAIF
integer code associated with the
body, must be present in the kernel
pool. This variable must be
associated with three numeric
values giving the lengths of the
ellipsoid's X, Y, and Z semi-axes.
"POINT" Treat the body as a single point.
When a point target is specified,
the occultation type must be
set to "ANY".
At least one of the target bodies `front' and `back' must
be modeled as an ellipsoid.
Case and leading or trailing blanks are not
significant in the string `fshape'.
fframe is the name of the body-fixed, body-centered reference
frame associated with the front target body. Examples
of such names are "IAU_SATURN" (for Saturn) and
"ITRF93" (for the Earth).
If the front target body is modeled as a point, `fframe'
should be left empty or blank.
Case and leading or trailing blanks bracketing a
non-blank frame name are not significant in the string
`fframe'.
back is the name of the target body that is occulted
by---that is, passes in back of---the other.
Optionally, you may supply the integer NAIF ID code
for the body as a string. For example both "MOON" and
"301" are legitimate strings that designate the Moon.
Case and leading or trailing blanks are not
significant in the string `back'.
bshape is the shape specification for the body designated by
`back'. The supported options are those for `fshape'. See
the description of `fshape' above for details.
bframe is the name of the body-fixed, body-centered reference
frame associated with the ``back'' target body.
Examples of such names are "IAU_SATURN" (for Saturn)
and "ITRF93" (for the Earth).
If the back target body is modeled as a point, `bframe'
should be left empty or blank.
Case and leading or trailing blanks bracketing a
non-blank frame name are not significant in the string
`bframe'.
abcorr indicates the aberration corrections to be applied to
the state of each target body to account for one-way
light time. Stellar aberration corrections are
ignored if specified, since these corrections don't
improve the accuracy of the occultation determination.
See the header of the SPICE routine spkezr_c for a
detailed description of the aberration correction
options. For convenience, the options supported by
this routine are listed below:
"NONE" Apply no correction.
"LT" "Reception" case: correct for
one-way light time using a Newtonian
formulation.
"CN" "Reception" case: converged
Newtonian light time correction.
"XLT" "Transmission" case: correct for
one-way light time using a Newtonian
formulation.
"XCN" "Transmission" case: converged
Newtonian light time correction.
Case and blanks are not significant in the string
`abcorr'.
obsrvr is the name of the body from which the occultation is
observed. Optionally, you may supply the integer NAIF
ID code for the body as a string.
Case and leading or trailing blanks are not
significant in the string `obsrvr'.
step is the step size to be used in the search. `step' must
be shorter than any interval, within the confinement
window, over which the specified condition is met. In
other words, `step' must be shorter than the shortest
occultation event that the user wishes to detect; `step'
must also be shorter than the shortest time interval
between two occultation events that occur within the
confinement window (see below). However, `step' must not
be *too* short, or the search will take an unreasonable
amount of time.
The choice of `step' affects the completeness but not the
precision of solutions found by this routine; the
precision is controlled by the convergence tolerance. See
the discussion of the parameter SPICE_GF_CNVTOL for
details.
`step' has units of TDB seconds.
cnfine is a SPICE window that confines the time period over
which the specified search is conducted. `cnfine' may
consist of a single interval or a collection of
intervals.
The endpoints of the time intervals comprising `cnfine'
are interpreted as seconds past J2000 TDB.
See the Examples section below for a code example
that shows how to create a confinement window.
-Detailed_Output
cnfine is the input confinement window, updated if necessary
so the control area of its data array indicates the
window's size and cardinality. The window data are
unchanged.
result is a SPICE window representing the set of time
intervals, within the confinement period, when the
specified occultation occurs.
The endpoints of the time intervals comprising `result'
are interpreted as seconds past J2000 TDB.
If `result' is non-empty on input, its contents
will be discarded before gfoclt_c conducts its
search.
-Parameters
SPICE_GF_CNVTOL
is the convergence tolerance used for finding endpoints
of the intervals comprising the result window.
SPICE_GF_CNVTOL is used to determine when binary searches
for roots should terminate: when a root is bracketed
within an interval of length SPICE_GF_CNVTOL, the root is
considered to have been found.
The accuracy, as opposed to precision, of roots found
by this routine depends on the accuracy of the input
data. In most cases, the accuracy of solutions will be
inferior to their precision.
SPICE_GF_CNVTOL is declared in the header file
SpiceGF.h
-Exceptions
1) In order for this routine to produce correct results,
the step size must be appropriate for the problem at hand.
Step sizes that are too large may cause this routine to miss
roots; step sizes that are too small may cause this routine
to run unacceptably slowly and in some cases, find spurious
roots.
This routine does not diagnose invalid step sizes, except
that if the step size is non-positive, the error
SPICE(INVALIDSTEPSIZE) will be signaled.
2) Due to numerical errors, in particular,
- Truncation error in time values
- Finite tolerance value
- Errors in computed geometric quantities
it is *normal* for the condition of interest to not always be
satisfied near the endpoints of the intervals comprising the
result window.
The result window may need to be contracted slightly by the
caller to achieve desired results. The SPICE window routine
wncond_c can be used to contract the result window.
3) If name of either target or the observer cannot be translated
to a NAIF ID code, the error will be diagnosed by a routine
in the call tree of this routine.
4) If the radii of a target body modeled as an ellipsoid cannot
be determined by searching the kernel pool for a kernel
variable having a name of the form
"BODYnnn_RADII"
where nnn represents the NAIF integer code associated with
the body, the error will be diagnosed by a routine in the
call tree of this routine.
5) If either of the target bodies `front' or `back' coincides with
the observer body `obsrvr', the error will be diagnosed by a
routine in the call tree of this routine.
6) If the body designated by `front' coincides with that
designated by `back', the error will be diagnosed by a routine
in the call tree of this routine.
7) If either of the body model specifiers `fshape' or `bshape'
is not recognized, the error will be diagnosed by a routine
in the call tree of this routine.
8) If both of the body model specifiers `fshape' and `bshape'
specify point targets, the error will be diagnosed by a
routine in the call tree of this routine.
9) If a target body-fixed reference frame associated with a
non-point target is not recognized, the error will be
diagnosed by a routine in the call tree of this routine.
10) If a target body-fixed reference frame is not centered at
the corresponding target body, the error will be
diagnosed by a routine in the call tree of this routine.
11) If the loaded kernels provide insufficient data to
compute any required state vector, the deficiency will
be diagnosed by a routine in the call tree of this routine.
12) If an error occurs while reading an SPK or other kernel file,
the error will be diagnosed by a routine in the call tree
of this routine.
13) If the output SPICE window `result' has insufficient capacity
to contain the number of intervals on which the specified
occultation condition is met, the error will be diagnosed
by a routine in the call tree of this routine.
14) If a point target is specified and the occultation
type is set to a valid value other than "ANY", the
error will be diagnosed by a routine in the call tree
of this routine.
15) Invalid occultation types will be diagnosed by a routine in
the call tree of this routine.
16) Invalid aberration correction specifications will be
diagnosed by a routine in the call tree of this routine.
17) If any input string argument pointer is null, the error
SPICE(NULLPOINTER) will be signaled.
18) If any input string argument, other than `fframe' or `bframe',
is empty, the error SPICE(EMPTYSTRING) will be signaled.
-Files
Appropriate SPICE kernels must be loaded by the calling program
before this routine is called.
The following data are required:
- SPK data: the calling application must load ephemeris data
for the target, source and observer that cover the time
period specified by the window `cnfine'. If aberration
corrections are used, the states of target and observer
relative to the solar system barycenter must be calculable
from the available ephemeris data. Typically ephemeris data
are made available by loading one or more SPK files via
furnsh_c.
- PCK data: bodies modeled as triaxial ellipsoids must have
semi-axis lengths provided by variables in the kernel pool.
Typically these data are made available by loading a text
PCK file via furnsh_c.
- FK data: if either of the reference frames designated by
`bframe' or `fframe' are not built in to the SPICE system,
one or more FKs specifying these frames must be loaded.
Kernel data are normally loaded once per program run, NOT every time
this routine is called.
-Particulars
This routine provides a simpler, but less flexible, interface
than does the CSPICE routine gfocce_c for conducting searches for
occultation events. Applications that require support for
progress reporting, interrupt handling, non-default step or
refinement functions, or non-default convergence tolerance should
call gfocce_c rather than this routine.
This routine determines a set of one or more time intervals
within the confinement window when a specified type of
occultation occurs. The resulting set of intervals is returned as
a SPICE window.
Below we discuss in greater detail aspects of this routine's
solution process that are relevant to correct and efficient
use of this routine in user applications.
The Search Process
==================
The search for occultations is treated as a search for state
transitions: times are sought when the state of the `back' body
changes from "not occulted" to "occulted" or vice versa.
Step Size
=========
Each interval of the confinement window is searched as follows:
first, the input step size is used to determine the time separation
at which the occultation state will be sampled. Starting at the left
endpoint of the interval, samples of the occultation state will be
taken at each step. If a state change is detected, a root has been
bracketed; at that point, the "root"--the time at which the state
change occurs---is found by a refinement process, for example, via
binary search.
Note that the optimal choice of step size depends on the lengths
of the intervals over which the occultation state is constant:
the step size should be shorter than the shortest occultation
duration and the shortest period between occultations, within
the confinement window.
Having some knowledge of the relative geometry of the targets and
observer can be a valuable aid in picking a reasonable step size.
In general, the user can compensate for lack of such knowledge by
picking a very short step size; the cost is increased computation
time.
Note that the step size is not related to the precision with which
the endpoints of the intervals of the result window are computed.
That precision level is controlled by the convergence tolerance.
Convergence Tolerance
=====================
Once a root has been bracketed, a refinement process is used to
narrow down the time interval within which the root must lie. This
refinement process terminates when the location of the root has been
determined to within an error margin called the "convergence
tolerance." The convergence tolerance used by this routine is set
via the parameter SPICE_GF_CNVTOL.
The value of SPICE_GF_CNVTOL is set to a "tight" value so that the
tolerance doesn't limit the accuracy of solutions found by this
routine. In general the accuracy of input data will be the limiting
factor.
To use a different tolerance value, a lower-level GF routine such as
gfocce_c must be called. Making the tolerance tighter than
SPICE_GF_CNVTOL is unlikely to be useful, since the results are
unlikely to be more accurate. Making the tolerance looser will speed
up searches somewhat, since a few convergence steps will be omitted.
However, in most cases, the step size is likely to have a much
greater effect on processing time than would the convergence
tolerance.
The Confinement Window
======================
The simplest use of the confinement window is to specify a time
interval within which a solution is sought.
The confinement window also can be used to restrict a search to
a time window over which required data (typically ephemeris
data, in the case of occultation searches) are known to be
available.
In some cases, the confinement window be used to make searches
more efficient. Sometimes it's possible to do an efficient search
to reduce the size of the time period over which a relatively
slow search of interest must be performed. See the "CASCADE"
example program in gf.req for a demonstration.
-Examples
The numerical results shown for these examples may differ across
platforms. The results depend on the SPICE kernels used as
input, the compiler and supporting libraries, and the machine
specific arithmetic implementation.
1) Find occultations of the Sun by the Moon (that is, solar
eclipses) as seen from the center of the Earth over the month
December, 2001.
Use light time corrections to model apparent positions of Sun
and Moon. Stellar aberration corrections are not specified
because they don't affect occultation computations.
We select a step size of 3 minutes, which means we
ignore occultation events lasting less than 3 minutes,
if any exist.
Use the meta-kernel shown below to load the required SPICE
kernels.
KPL/MK
File name: standard.tm
This meta-kernel is intended to support operation of SPICE
example programs. The kernels shown here should not be
assumed to contain adequate or correct versions of data
required by SPICE-based user applications.
In order for an application to use this meta-kernel, the
kernels referenced here must be present in the user's
current working directory.
\begindata
KERNELS_TO_LOAD = ( 'de421.bsp',
'pck00008.tpc',
'naif0009.tls' )
\begintext
Example code begins here.
#include <stdio.h>
#include "SpiceUsr.h"
int main()
{
/.
Local constants
./
#define TIMFMT "YYYY MON DD HR:MN:SC.###### (TDB)::TDB"
#define MAXWIN 200
#define TIMLEN 41
/.
Local variables
./
SPICEDOUBLE_CELL ( cnfine, MAXWIN );
SPICEDOUBLE_CELL ( result, MAXWIN );
SpiceChar * win0;
SpiceChar * win1;
SpiceChar begstr [ TIMLEN ];
SpiceChar endstr [ TIMLEN ];
SpiceDouble et0;
SpiceDouble et1;
SpiceDouble left;
SpiceDouble right;
SpiceDouble step;
SpiceInt i;
/.
Load kernels.
./
furnsh_c ( "standard.tm" );
/.
Obtain the TDB time bounds of the confinement
window, which is a single interval in this case.
./
win0 = "2001 DEC 01 00:00:00 TDB";
win1 = "2002 JAN 01 00:00:00 TDB";
str2et_c ( win0, &et0 );
str2et_c ( win1, &et1 );
/.
Insert the time bounds into the confinement
window.
./
wninsd_c ( et0, et1, &cnfine );
/.
Select a 3-minute step. We'll ignore any occultations
lasting less than 3 minutes. Units are TDB seconds.
./
step = 180.0;
/.
Perform the search.
./
gfoclt_c ( "any",
"moon", "ellipsoid", "iau_moon",
"sun", "ellipsoid", "iau_sun",
"lt", "earth", step,
&cnfine, &result );
if ( wncard_c(&result) == 0 )
{
printf ( "No occultation was found.\n" );
}
else
{
for ( i = 0; i < wncard_c(&result); i++ )
{
/.
Fetch and display each occultation interval.
./
wnfetd_c ( &result, i, &left, &right );
timout_c ( left, TIMFMT, TIMLEN, begstr );
timout_c ( right, TIMFMT, TIMLEN, endstr );
printf ( "Interval %ld\n"
" Start time: %s\n"
" Stop time: %s\n",
i, begstr, endstr );
}
}
return ( 0 );
}
When this program was executed on a PC/Linux/gcc platform, the
output was:
Interval 0
Start time: 2001 DEC 14 20:10:14.195952 (TDB)
Stop time: 2001 DEC 14 21:35:50.317994 (TDB)
2) Find occultations of Titan by Saturn or of Saturn by
Titan as seen from the center of the Earth over the
last four months of 2008. Model both target bodies as
ellipsoids. Search for every type of occultation.
Use light time corrections to model apparent positions of
Saturn and Titan. Stellar aberration corrections are not
specified because they don't affect occultation computations.
We select a step size of 15 minutes, which means we
ignore occultation events lasting less than 15 minutes,
if any exist.
Use the meta-kernel shown below to load the required SPICE
kernels.
KPL/MK
File name: gfoclt_ex2.tm
This meta-kernel is intended to support operation of SPICE
example programs. The kernels shown here should not be
assumed to contain adequate or correct versions of data
required by SPICE-based user applications.
In order for an application to use this meta-kernel, the
kernels referenced here must be present in the user's
current working directory.
The names and contents of the kernels referenced
by this meta-kernel are as follows:
File name Contents
--------- --------
de421.bsp Planetary ephemeris
sat288.bsp Satellite ephemeris for
Saturn
pck00008.tpc Planet orientation and
radii
naif0009.tls Leapseconds
\begindata
KERNELS_TO_LOAD = ( 'de421.bsp',
'sat288.bsp',
'pck00008.tpc',
'naif0009.tls' )
\begintext
End of meta-kernel
Example code begins here.
#include <stdio.h>
#include <string.h>
#include "SpiceUsr.h"
int main()
{
/.
Local constants
./
#define TIMFMT "YYYY MON DD HR:MN:SC.###### (TDB)::TDB"
#define MAXWIN 200
#define TIMLEN 41
#define LNSIZE 81
#define NTYPES 4
/.
Local variables
./
SPICEDOUBLE_CELL ( cnfine, MAXWIN );
SPICEDOUBLE_CELL ( result, MAXWIN );
SpiceChar * back;
SpiceChar * bframe;
SpiceChar * front;
SpiceChar * fframe;
SpiceChar line [ LNSIZE ];
SpiceChar * obsrvr;
SpiceChar * occtyp [ NTYPES ] =
{
"FULL",
"ANNULAR",
"PARTIAL",
"ANY"
};
SpiceChar * templt [ NTYPES ] =
{
"Condition: # occultation of # by #",
"Condition: # occultation of # by #",
"Condition: # occultation of # by #",
"Condition: # occultation of # by #"
};
SpiceChar timstr [ TIMLEN ];
SpiceChar title [ LNSIZE ];
SpiceChar * win0;
SpiceChar * win1;
SpiceDouble et0;
SpiceDouble et1;
SpiceDouble finish;
SpiceDouble start;
SpiceDouble step;
SpiceInt i;
SpiceInt j;
SpiceInt k;
/.
Load kernels.
./
furnsh_c ( "gfoclt_ex2.tm" );
/.
Obtain the TDB time bounds of the confinement
window, which is a single interval in this case.
./
win0 = "2008 SEP 01 00:00:00 TDB";
win1 = "2009 JAN 01 00:00:00 TDB";
str2et_c ( win0, &et0 );
str2et_c ( win1, &et1 );
/.
Insert the time bounds into the confinement
window.
./
wninsd_c ( et0, et1, &cnfine );
/.
Select a 15-minute step. We'll ignore any occultations
lasting less than 15 minutes. Units are TDB seconds.
./
step = 900.0;
/.
The observation location is the Earth.
./
obsrvr = "Earth";
/.
Loop over the occultation types.
./
for ( i = 0; i < NTYPES; i++ )
{
/.
For each type, do a search for both transits of
Titan across Saturn and occultations of Titan by
Saturn.
./
for ( j = 0; j < 2; j++ )
{
if ( j == 0 )
{
front = "TITAN";
fframe = "IAU_TITAN";
back = "SATURN";
bframe = "IAU_SATURN";
}
else
{
front = "SATURN";
fframe = "IAU_SATURN";
back = "TITAN";
bframe = "IAU_TITAN";
}
/.
Perform the search. The target body shapes
are modeled as ellipsoids.
./
gfoclt_c ( occtyp[i],
front, "ellipsoid", fframe,
back, "ellipsoid", bframe,
"lt", obsrvr, step,
&cnfine, &result );
/.
Display the results.
./
printf ( "\n" );
/.
Substitute the occultation type and target
body names into the title string:
./
repmc_c ( templt[i], "#", occtyp[i], LNSIZE, title );
repmc_c ( title, "#", back, LNSIZE, title );
repmc_c ( title, "#", front, LNSIZE, title );
printf ( "%s\n", title );
if ( wncard_c(&result) == 0 )
{
printf ( " Result window is empty: "
"no occultation was found.\n" );
}
else
{
printf ( " Result window start, stop times:\n" );
for ( k = 0; k < wncard_c(&result); k++ )
{
/.
Fetch the endpoints of the kth interval
of the result window.
./
wnfetd_c ( &result, k, &start, &finish );
/.
Call strncpy with a length of 7 to include
a terminating null.
./
strncpy ( line, " # #", 7 );
timout_c ( start, TIMFMT, TIMLEN, timstr );
repmc_c ( line, "#", timstr, LNSIZE, line );
timout_c ( finish, TIMFMT, TIMLEN, timstr );
repmc_c ( line, "#", timstr, LNSIZE, line );
printf ( "%s\n", line );
}
}
/.
We've finished displaying the results of the
current search.
./
}
/.
We've finished displaying the results of the
searches using the current occultation type.
./
}
printf ( "\n" );
return ( 0 );
}
When this program was executed on a PC/Linux/gcc platform, the
output was:
Condition: FULL occultation of SATURN by TITAN
Result window is empty: no occultation was found.
Condition: FULL occultation of TITAN by SATURN
Result window start, stop times:
2008 OCT 27 22:08:01.627053 (TDB) 2008 OCT 28 01:05:03.375236 (TDB)
2008 NOV 12 21:21:59.252262 (TDB) 2008 NOV 13 02:06:05.053051 (TDB)
2008 NOV 28 20:49:02.402832 (TDB) 2008 NOV 29 02:13:58.986344 (TDB)
2008 DEC 14 20:05:09.246177 (TDB) 2008 DEC 15 01:44:53.523002 (TDB)
2008 DEC 30 19:00:56.577073 (TDB) 2008 DEC 31 00:42:43.222909 (TDB)
Condition: ANNULAR occultation of SATURN by TITAN
Result window start, stop times:
2008 OCT 19 21:29:20.599087 (TDB) 2008 OCT 19 22:53:34.518737 (TDB)
2008 NOV 04 20:15:38.620368 (TDB) 2008 NOV 05 00:18:59.139978 (TDB)
2008 NOV 20 19:38:59.647712 (TDB) 2008 NOV 21 00:35:26.725908 (TDB)
2008 DEC 06 18:58:34.073268 (TDB) 2008 DEC 07 00:16:17.647040 (TDB)
2008 DEC 22 18:02:46.288289 (TDB) 2008 DEC 22 23:26:52.712459 (TDB)
Condition: ANNULAR occultation of TITAN by SATURN
Result window is empty: no occultation was found.
Condition: PARTIAL occultation of SATURN by TITAN
Result window start, stop times:
2008 OCT 19 20:44:30.326771 (TDB) 2008 OCT 19 21:29:20.599087 (TDB)
2008 OCT 19 22:53:34.518737 (TDB) 2008 OCT 19 23:38:26.250580 (TDB)
2008 NOV 04 19:54:40.339331 (TDB) 2008 NOV 04 20:15:38.620368 (TDB)
2008 NOV 05 00:18:59.139978 (TDB) 2008 NOV 05 00:39:58.612935 (TDB)
2008 NOV 20 19:21:46.689523 (TDB) 2008 NOV 20 19:38:59.647712 (TDB)
2008 NOV 21 00:35:26.725908 (TDB) 2008 NOV 21 00:52:40.604703 (TDB)
2008 DEC 06 18:42:36.100544 (TDB) 2008 DEC 06 18:58:34.073268 (TDB)
2008 DEC 07 00:16:17.647040 (TDB) 2008 DEC 07 00:32:16.324244 (TDB)
2008 DEC 22 17:47:10.776722 (TDB) 2008 DEC 22 18:02:46.288289 (TDB)
2008 DEC 22 23:26:52.712459 (TDB) 2008 DEC 22 23:42:28.850542 (TDB)
Condition: PARTIAL occultation of TITAN by SATURN
Result window start, stop times:
2008 OCT 27 21:37:16.970175 (TDB) 2008 OCT 27 22:08:01.627053 (TDB)
2008 OCT 28 01:05:03.375236 (TDB) 2008 OCT 28 01:35:49.266506 (TDB)
2008 NOV 12 21:01:47.105498 (TDB) 2008 NOV 12 21:21:59.252262 (TDB)
2008 NOV 13 02:06:05.053051 (TDB) 2008 NOV 13 02:26:18.227357 (TDB)
2008 NOV 28 20:31:28.522707 (TDB) 2008 NOV 28 20:49:02.402832 (TDB)
2008 NOV 29 02:13:58.986344 (TDB) 2008 NOV 29 02:31:33.691598 (TDB)
2008 DEC 14 19:48:27.094229 (TDB) 2008 DEC 14 20:05:09.246177 (TDB)
2008 DEC 15 01:44:53.523002 (TDB) 2008 DEC 15 02:01:36.360243 (TDB)
2008 DEC 30 18:44:23.485898 (TDB) 2008 DEC 30 19:00:56.577073 (TDB)
2008 DEC 31 00:42:43.222909 (TDB) 2008 DEC 31 00:59:17.030568 (TDB)
Condition: ANY occultation of SATURN by TITAN
Result window start, stop times:
2008 OCT 19 20:44:30.326771 (TDB) 2008 OCT 19 23:38:26.250580 (TDB)
2008 NOV 04 19:54:40.339331 (TDB) 2008 NOV 05 00:39:58.612935 (TDB)
2008 NOV 20 19:21:46.689523 (TDB) 2008 NOV 21 00:52:40.604703 (TDB)
2008 DEC 06 18:42:36.100544 (TDB) 2008 DEC 07 00:32:16.324244 (TDB)
2008 DEC 22 17:47:10.776722 (TDB) 2008 DEC 22 23:42:28.850542 (TDB)
Condition: ANY occultation of TITAN by SATURN
Result window start, stop times:
2008 OCT 27 21:37:16.970175 (TDB) 2008 OCT 28 01:35:49.266506 (TDB)
2008 NOV 12 21:01:47.105498 (TDB) 2008 NOV 13 02:26:18.227357 (TDB)
2008 NOV 28 20:31:28.522707 (TDB) 2008 NOV 29 02:31:33.691598 (TDB)
2008 DEC 14 19:48:27.094229 (TDB) 2008 DEC 15 02:01:36.360243 (TDB)
2008 DEC 30 18:44:23.485898 (TDB) 2008 DEC 31 00:59:17.030568 (TDB)
-Restrictions
The kernel files to be used by gfoclt_c must be loaded (normally via
the CSPICE routine furnsh_c) before gfoclt_c is called.
-Literature_References
None.
-Author_and_Institution
N. J. Bachman (JPL)
L. S. Elson (JPL)
E. D. Wright (JPL)
-Version
-CSPICE Version 1.0.0, 07-APR-2009 (NJB) (LSE) (EDW)
-Index_Entries
GF occultation search
-&
*/
{ /* Begin gfoclt_c */
/*
Local variables
*/
static const SpiceChar * blankStr = " ";
SpiceChar * bFrameStr;
SpiceChar * fFrameStr;
/*
Participate in error tracing.
*/
if ( return_c() )
{
return;
}
chkin_c ( "gfoclt_c" );
/*
Make sure cell data types are d.p.
*/
CELLTYPECHK2 ( CHK_STANDARD, "gfoclt_c", SPICE_DP, cnfine, result );
/*
Initialize the input cells if necessary.
*/
CELLINIT2 ( cnfine, result );
/*
The input frame names are special cases because we allow the caller
to pass in empty strings. If either of these strings are empty,
we pass a null-terminated string containing one blank character to
the underlying f2c'd routine.
First make sure the frame name pointers are non-null.
*/
CHKPTR ( CHK_STANDARD, "gfoclt_c", bframe );
CHKPTR ( CHK_STANDARD, "gfoclt_c", fframe );
/*
Use the input frame strings if they're non-empty; otherwise
use blank strings for the frame names.
*/
if ( bframe[0] )
{
bFrameStr = (SpiceChar *) bframe;
}
else
{
bFrameStr = (SpiceChar *) blankStr;
}
if ( fframe[0] )
{
fFrameStr = (SpiceChar *) fframe;
}
else
{
fFrameStr = (SpiceChar *) blankStr;
}
/*
Check the other input strings to make sure each pointer is non-null
and each string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "gfoclt_c", occtyp );
CHKFSTR ( CHK_STANDARD, "gfoclt_c", front );
CHKFSTR ( CHK_STANDARD, "gfoclt_c", fshape );
CHKFSTR ( CHK_STANDARD, "gfoclt_c", back );
CHKFSTR ( CHK_STANDARD, "gfoclt_c", bshape );
CHKFSTR ( CHK_STANDARD, "gfoclt_c", abcorr );
CHKFSTR ( CHK_STANDARD, "gfoclt_c", obsrvr );
/*
Let the f2c'd routine do the work.
*/
gfoclt_ ( (char *) occtyp,
(char *) front,
(char *) fshape,
(char *) fFrameStr,
(char *) back,
(char *) bshape,
(char *) bFrameStr,
(char *) abcorr,
(char *) obsrvr,
(doublereal *) &step,
(doublereal *) cnfine->base,
(doublereal *) result->base,
(ftnlen ) strlen(occtyp),
(ftnlen ) strlen(front),
(ftnlen ) strlen(fshape),
(ftnlen ) strlen(fframe),
(ftnlen ) strlen(back),
(ftnlen ) strlen(bshape),
(ftnlen ) strlen(bframe),
(ftnlen ) strlen(abcorr),
(ftnlen ) strlen(obsrvr) );
/*
Sync the output result cell.
*/
if ( !failed_c() )
{
zzsynccl_c ( F2C, result );
}
chkout_c ( "gfoclt_c" );
} /* End gfoclt_c */
void ekrcec_c ( SpiceInt handle,
SpiceInt segno,
SpiceInt recno,
ConstSpiceChar * column,
SpiceInt lenout,
SpiceInt * nvals,
void * cvals,
SpiceBoolean * isnull )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
handle I Handle attached to EK file.
segno I Index of segment containing record.
recno I Record from which data is to be read.
column I Column name.
lenout I Maximum length of output strings.
nvals O Number of values in column entry.
cvals O Character values in column entry.
isnull O Flag indicating whether column entry is null.
-Detailed_Input
handle is an EK file handle. The file may be open for
read or write access.
segno is the index of the segment from which data is to
be read. The first segment in the file has index 0.
recno is the index of the record from which data is to be
read. This record number is relative to the start
of the segment indicated by segno; the first
record in the segment has index 0.
column is the name of the column from which data is to be
read.
lenout is the maximum string length that can be accommodated in
the output array cvals. This length must large enough to
hold the longest element of the specified column entry,
including a null terminator. If the column element contains
strings of length up to n characters, lenout should be set
to n + 1.
-Detailed_Output
nvals,
cvals are, respectively, the number of values found in
the specified column entry and the set of values
themselves. The array cvals must have sufficient
string length to accommodate the longest string
in the returned column entry. The calling application
should declare cvals with dimension
[nelts][lenout]
where nelts is the maximum number of elements that
occur in any entry of the specified column.
For columns having fixed-size entries, when a
a column entry is null, nvals is still set to the
column entry size. For columns having variable-
size entries, nvals is set to 1 for null entries.
isnull is a logical flag indicating whether the returned
column entry is null.
-Parameters
None.
-Exceptions
1) If handle is invalid, the error will be diagnosed by routines
called by this routine.
2) If segno is out of range, the error will diagnosed by routines
called by this routine.
3) If recno is out of range, the error will diagnosed by routines
called by this routine.
4) If column is not the name of a declared column, the error
will be diagnosed by routines called by this routine.
5) If column specifies a column of whose data type is not
character, the error SPICE(WRONGDATATYPE) will be
signaled.
6) If column specifies a column of whose class is not
a character class known to this routine, the error
SPICE(NOCLASS) will be signaled.
7) If an attempt is made to read an uninitialized column entry,
the error will be diagnosed by routines called by this
routine. A null entry is considered to be initialized, but
entries do not contain null values by default.
8) If an I/O error occurs while reading or writing the indicated
file, the error will be diagnosed by routines called by this
routine.
9) If any element of the column entry would be truncated when
assigned to an element of cvals, the error will be diagnosed
by routines called by this routine.
10) If the input column name string pointer is null, the error
SPICE(NULLPOINTER) will be signaled.
11) If the input column name string has length zero, the error
SPICE(EMPTYSTRING) will be signaled.
12) If the output string pointer cvals is null, the error SPICE(NULLPOINTER)
will be signaled.
13) If the output string length indicated by lenout is less than two
characters, it is too short to contain one character of output data
plus a null terminator, so it cannot be passed to the underlying Fortran
routine. In this event, the error SPICE(STRINGTOOSHORT) is
signaled.
-Files
See the EK Required Reading for a discussion of the EK file
format.
-Particulars
This routine is a utility that allows an EK file to be read
directly without using the high-level query interface.
-Examples
1) Read the value in the third record of the column ccol in
the fifth segment of an EK file designated by handle.
#include "SpiceUsr.h"
.
.
.
ekrcec_c ( handle, 4, 2, "CCOL", lenout, &nvals, &cval, &isnull );
-Restrictions
1) EK files open for write access are not necessarily readable.
In particular, a column entry can be read only if it has been
initialized. The caller is responsible for determining
when it is safe to read from files open for write access.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
-Version
-CSPICE Version 1.1.0, 21-MAY-2001 (WLT)
Added a cast to (char *) in the call to F2C_ConvertStrArr to
support compilation under C++.
-CSPICE Version 1.0.0, 04-JUL-2000 (NJB)
-Index_Entries
read character data from EK column
-&
*/
{ /* Begin ekrcec_c */
/*
Local variables
*/
logical null;
/*
Participate in error tracing.
*/
chkin_c ( "ekrcec_c" );
/*
Check the column name to make sure the pointer is non-null
and the string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "ekrcec_c", column );
/*
Make sure the output array has at least enough room for one output
character and a null terminator. Also check for a null pointer.
*/
CHKOSTR ( CHK_STANDARD, "ekrcec_c", cvals, lenout );
/*
Map the segment and record numbers to their Fortran-style
values. Pass a flag of type logical to ekrced_.
*/
segno++;
recno++;
ekrcec_ ( ( integer * ) &handle,
( integer * ) &segno,
( integer * ) &recno,
( char * ) column,
( integer * ) nvals,
( char * ) cvals,
( logical * ) &null,
( ftnlen ) strlen(column),
( ftnlen ) lenout-1 );
/*
Convert the output array from Fortran to C style.
*/
F2C_ConvertStrArr ( *nvals, lenout, (char *) cvals );
/*
Cast the null flag back to a SpiceBoolean.
*/
*isnull = null;
chkout_c ( "ekrcec_c" );
} /* End ekrcec_c */
void spkw10_c ( SpiceInt handle,
SpiceInt body,
SpiceInt center,
ConstSpiceChar * frame,
SpiceDouble first,
SpiceDouble last,
ConstSpiceChar * segid,
ConstSpiceDouble consts [8],
SpiceInt n,
ConstSpiceDouble elems [],
ConstSpiceDouble epochs [] )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
handle I The handle of a DAF file open for writing.
body I The NAIF ID code for the body of the segment.
center I The center of motion for body.
frame I The reference frame for this segment.
first I The first epoch for which the segment is valid.
last I The last epoch for which the segment is valid.
segid I The string to use for segment identifier.
consts I The array of geophysical constants for the segment
n I The number of element/epoch pairs to be stored
elems I The collection of "two-line" element sets.
epochs I The epochs associated with the element sets.
-Detailed_Input
handle is the file handle of an SPK file that has been
opened for writing by spcopn, dafopn, or dafopw.
body is the NAIF ID for the body whose states are
to be recorded in an SPK file.
center is the NAIF ID for the center of motion associated
with body.
frame is the reference frame that states are referenced to,
for example "J2000".
first are the bounds on the ephemeris times, expressed as
last seconds past J2000, for which the states can be used
to interpolate a state for body.
segid is the segment identifier. An SPK segment identifier
may contain up to 40 characters.
consts are the geophysical constants needed for evaluation
of the two line elements sets. The order of these
constants must be:
consts[0] = J2 gravitational harmonic for earth
consts[1] = J3 gravitational harmonic for earth
consts[2] = J4 gravitational harmonic for earth
consts[3] = Square root of the GM for earth where GM
is expressed in earth radii cubed per
minutes squared
consts[4] = Equatorial radius of the earth in km
consts[5] = Low altitude bound for atmospheric
model in km
consts[6] = High altitude bound for atmospheric
model in km
consts[7] = Distance units/earth radius (normally 1)
n is the number of "two-line" element sets and epochs
to be stored in the segment.
elems contains a time-ordered array of two-line elements
as supplied in NORAD two-line element files. The
i'th set of elements (where i ranges from 1 to n)
should be stored as shown here:
base = (i-1)*10
elems ( base + 0 ) = NDT20
elems ( base + 1 ) = NDD60
elems ( base + 2 ) = BSTAR
elems ( base + 3 ) = INCL
elems ( base + 4 ) = NODE0
elems ( base + 5 ) = ECC
elems ( base + 6 ) = OMEGA
elems ( base + 7 ) = MO
elems ( base + 8 ) = NO
elems ( base + 9 ) = EPOCH
The meaning of these variables is defined by the
format of the two-line element files available from
NORAD.
epochs contains the epochs (ephemeris seconds past J2000)
corresponding to the elements in elems. The I'th
epoch must equal the epoch of the I'th element set
Epochs must form a strictly increasing sequence.
-Detailed_Output
None. The data input is stored in an SPK segment in the
DAF connected to the input handle.
-Parameters
None.
-Particulars
This routine writes a type 10 SPK segment to the DAF open
for writing that is attached to handle. A routine, GETELM, that
reads two-line element data from files distributed by
NORAD is available from NAIF.
-Examples
Suppose that you have collected the two-line element data
and geophysical constants as prescribed above. The following
code fragment demonstrates how you could go about creating
a type 10 SPK segment.
#include "SpiceUsr.h"
.
.
.
/.
Open a new SPK file using DAF and get a file handle.
./
body = <integer code for the body>;
center = <integer code for central body for the trajectory>;
frame = "J2000";
segid = <string that gives the bodies name>;
fname = "SAMPLE.SPK";
ifname = "SAMPLE SPK FILE FOR PRIVATE USE";
ncomch = 0;
void spkopn_c ( fname, ifname, ncomch, &handle );
/.
Add the type 10 data.
./
spkw10_c ( handle, body, center, frame, first, last,
segid, consts, n, elems, epochs );
/.
Close the SPK properly.
./
spkcls_c ( handle );
-Restrictions
None.
-Exceptions
1) Errors in the structure or content of the inputs must be
diagnosed by routines called by this one.
2) File access errors are diagnosed by routines in the
call tree of this routine.
3) If either the input frame or segment ID string pointer is null,
the error SPICE(NULLPOINTER) is signaled.
4) If either the input frame or segment ID string is empty,
the error SPICE(EMPTYSTRING) is signaled.
-Files
None.
-Author_and_Institution
N.J. Bachman (JPL)
W.L. Taber (JPL)
-Literature_References
None.
-Version
-CSPICE Version 1.0.1, 30-OCT-2006 (BVS)
Deleted "inertial" from the FRAME description in the Brief_I/O
section of the header.
-CSPICE Version 1.0.0, 29-JUN-1999 (NJB) (WLT)
-Index_Entries
write a type_10 spk segment
-&
*/
{ /* Begin spkw10_c */
/*
Participate in error tracing.
*/
chkin_c ( "spkw10_c" );
/*
Check the input strings to make sure the pointers
are non-null and the string lengths are non-zero.
*/
CHKFSTR ( CHK_STANDARD, "spkw10_c", frame );
CHKFSTR ( CHK_STANDARD, "spkw10_c", segid );
/*
Write the segment.
*/
spkw10_ ( ( integer * ) &handle,
( integer * ) &body,
( integer * ) ¢er,
( char * ) frame,
( doublereal * ) &first,
( doublereal * ) &last,
( char * ) segid,
( doublereal * ) consts,
( integer * ) &n,
( doublereal * ) elems,
( doublereal * ) epochs,
( ftnlen ) strlen(frame),
( ftnlen ) strlen(segid) );
chkout_c ( "spkw10_c" );
} /* End spkw10_c */
void bodvrd_c ( ConstSpiceChar * bodynm,
ConstSpiceChar * item,
SpiceInt maxn,
SpiceInt * dim,
SpiceDouble * values )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
bodynm I Body name.
item I Item for which values are desired. ("RADII",
"NUT_PREC_ANGLES", etc. )
maxn I Maximum number of values that may be returned.
dim O Number of values returned.
values O Values.
-Detailed_Input
bodynm is the name of the body for which `item' is requested.
`bodynm' is case-insensitive, and leading and trailing
blanks in `bodynm' are not significant. Optionally, you
may supply the integer ID code for the object as an
integer string. For example both "MOON" and "301" are
legitimate strings that indicate the moon is the body
of interest.
item is the item to be returned. Together, the NAIF ID
code of the body and the item name combine to form a
kernel variable name, e.g.,
"BODY599_RADII"
"BODY401_POLE_RA"
The values associated with the kernel variable having
the name constructed as shown are sought. Below
we'll take the shortcut of calling this kernel variable
the "requested kernel variable."
Note that `item' *is* case-sensitive. This attribute
is inherited from the case-sensitivity of kernel
variable names.
maxn is the maximum number of values that may be returned.
The output array `values' must be declared with size at
least `maxn'. It's an error to supply an output array
that is too small to hold all of the values associated
with the requested kernel variable.
-Detailed_Output
dim is the number of values returned; this is always the
number of values associated with the requested kernel
variable unless an error has been signaled.
values is the array of values associated with the requested
kernel variable. If `values' is too small to hold all
of the values associated with the kernel variable, the
returned values of `dim' and `values' are undefined.
-Parameters
None.
-Exceptions
1) If the input body name cannot be translated to an ID code,
and if the name is not a string representation of an integer
(for example, "399"), the error SPICE(NOTRANSLATION) is
signaled.
2) If the requested kernel variable is not found in the kernel
pool, the error SPICE(KERNELVARNOTFOUND) is signaled.
3) If the requested kernel variable is found but the associated
values aren't numeric, the error SPICE(TYPEMISMATCH) is
signaled.
4) The output array `values' must be declared with sufficient size
to contain all of the values associated with the requested kernel
variable. If the dimension of `values' indicated by `maxn' is
too small to contain the requested values, the error
SPICE(ARRAYTOOSMALL) is signaled.
5) If the input dimension `maxn' indicates there is more room
in `values' than there really is---for example, if `maxn' is
10 but `values' is declared with dimension 5---and the dimension
of the requested kernel variable is larger than the actual
dimension of `values', then this routine may overwrite
memory. The results are unpredictable.
6) If either of the input string pointers `bodynm' or `item'
are null, the error SPICE(NULLPOINTER) will be signaled.
7) If either of the input strings referred to by `bodynm' or `item'
contain no data characters, the error SPICE(EMPTYSTRING) will
be signaled.
-Files
None.
-Particulars
This routine simplifies looking up PCK kernel variables by
constructing names of requested kernel variables and by performing
error checking.
This routine is intended for use in cases where the maximum number
of values that may be returned is known at compile time. The caller
fetches all of the values associated with the specified kernel
variable via a single call to this routine. If the number of values
to be fetched cannot be known until run time, the lower-level
routine gdpool_c should be used instead. gdpool_c supports fetching
arbitrary amounts of data in multiple "chunks."
This routine is intended for use in cases where the requested kernel
variable is expected to be present in the kernel pool. If the
variable is not found or has the wrong data type, this routine
signals an error. In cases where it is appropriate to indicate
absence of an expected kernel variable by returning a boolean "found
flag" with the value SPICEFALSE, again the routine gdpool_c should
be used.
-Examples
1) When the kernel variable
BODY399_RADII
is present in the kernel pool---normally because a PCK
defining this variable has been loaded---the call
bodvrd_c ( "EARTH", "RADII", 3, &dim, values );
returns the dimension and values associated with the variable
"BODY399_RADII", for example,
dim == 3
value[0] == 6378.140
value[1] == 6378.140
value[2] == 6356.755
2) The call
bodvrd_c ( "earth", "RADII", 3, &dim, values );
will produce the same results shown in example (1),
since the case of the input argument `bodynm' is
not significant.
3) The call
bodvrd_c ( "399", "RADII", 3, &dim, values );
will produce the same results shown in example (1),
since strings containing integer codes are accepted
by this routine.
4) The call
bodvrd_c ( "EARTH", "radii", 3, &dim, values );
usually will cause a SPICE(KERNELVARNOTFOUND) error to be
signaled, because this call will attempt to look up the
values associated with a kernel variable of the name
"BODY399_radii"
Since kernel variable names are case sensitive, this
name is not considered to match the name
"BODY399_RADII"
which normally would be present after a text PCK
containing data for all planets and satellites has
been loaded.
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
B.V. Semenov (JPL)
W.L. Taber (JPL)
I.M. Underwood (JPL)
-Version
-CSPICE Version 1.0.1, 12-APR-2006 (NJB)
Header fix: output argument `dim' is now preceded by
an ampersand in example calls to bodvrd_c.c.
-CSPICE Version 1.0.0, 22-FEB-2004 (NJB)
-Index_Entries
fetch constants for a body from the kernel pool
physical constants for a body
-&
*/
{ /* Begin bodvrd_c */
/*
Participate in error tracing.
*/
if ( return_c() )
{
return;
}
chkin_c ( "bodvrd_c" );
/*
Check the input strings.
*/
CHKFSTR ( CHK_STANDARD, "bodvrd_c", bodynm );
CHKFSTR ( CHK_STANDARD, "bodvrd_c", item );
/*
Call the f2c'd SPICELIB function.
*/
bodvrd_ ( (char *) bodynm,
(char *) item,
(integer *) &maxn,
(integer *) dim,
(doublereal *) values,
(ftnlen ) strlen(bodynm),
(ftnlen ) strlen(item) );
chkout_c ( "bodvrd_c" );
} /* End bodvrd_c */
void ekbseg_c ( SpiceInt handle,
ConstSpiceChar * tabnam,
SpiceInt ncols,
SpiceInt cnmlen,
const void * cnames,
SpiceInt declen,
const void * decls,
SpiceInt * segno )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
handle I File handle.
tabnam I Table name.
ncols I Number of columns in the segment.
cnmlen I Length of names in in column name array.
cnames I Names of columns.
declen I Length of declaration strings in declaration array.
decls I Declarations of columns.
segno O Segment number.
-Detailed_Input
handle the handle of an EK file that is open for writing.
tabnam is the name of the EK table to which the current
segment belongs. All segments in the EK file
designated by handle must have identical column
attributes. tabnam must not exceed SPICE_EK_TNAMSZ
characters (see SpiceEK.h) in length. Case is not
significant. Table names must start with a letter and
contain only characters from the set
{A-Z,a-z,0-9,$,_}.
ncols is the number of columns in a new segment.
cnmlen,
cnames are, respectively, the length of the column name
strings in the column name array, and the base
address of the array itself. The array should have
dimensions
[ncols][cnmlen]
declen,
decls are, respectively, the length of the declaration
strings in the declaration array, and the base
address of the array itself. The array should have
dimensions
[ncols][declen]
The Ith element of cnames and the Ith element of decls
apply to the Ith column in the segment.
Column names must not exceed CSPICE_EK_CNAMSZ
characters (see SpiceEK.h) in length. Case is not
significant. Column names must start with a letter
and contain only characters from the set
{A-Z,a-z,0-9,$,_}.
The declarations are strings that contain
"keyword=value" assignments that define the
attributes of the columns to which they apply. The
column attributes that are defined by a column
declaration are:
DATATYPE
SIZE
<is the column indexed?>
<does the column allow null values?>
The form of a declaration is
"DATATYPE = <type>,
SIZE = <size>,
INDEXED = <boolean>,
NULLS_OK = <boolean>"
For example, an indexed, scalar, integer column
that allows null values would have the declaration
"DATATYPE = INTEGER,
SIZE = 1,
INDEXED = TRUE,
NULLS_OK = TRUE"
Commas are required to separate the assignments
within declarations; white space is optional;
case is not significant.
The order in which the attribute keywords are
listed in declaration is not significant.
Every column in a segment must be declared.
Each column entry is effectively an array, each
element of which has the declared data type. The
SIZE keyword indicates how many elements are in
each entry of the column in whose declaration the
keyword appears. Note that only scalar-valued
columns (those for which SIZE = 1) may be
referenced in query constraints. A size
assignment has the syntax
SIZE = <integer>
or
SIZE = VARIABLE
The size value defaults to 1 if omitted.
The DATATYPE keyword defines the data type of
column entries. The DATATYPE assignment syntax
has any of the forms
DATATYPE = CHARACTER*(<length>)
DATATYPE = CHARACTER*(*)
DATATYPE = DOUBLE PRECISION
DATATYPE = INTEGER
DATATYPE = TIME
As the datatype declaration syntax suggests,
character strings may have fixed or variable
length. Variable-length strings are allowed only
in columns of size 1.
Optionally, scalar-valued columns may be indexed.
To create an index for a column, use the assignment
INDEXED = TRUE
By default, columns are not indexed.
Optionally, any column can allow null values. To
indicate that a column may allow null values, use
the assigment
NULLS_OK = TRUE
in the column declaration. By default, null
values are not allowed in column entries.
-Detailed_Output
segno is the number of the segment to which data is to be
added. Segments are numbered from 0 to nseg-1, where
nseg is the count of segments in the file. Segment
numbers are used as unique identifiers by other EK
access routines.
-Parameters
None.
-Exceptions
1) If handle is invalid, the error will be diagnosed by routines
called by this routine.
2) If tabnam is more than SPICE_EK_TNAMSZ characters long, the
error is diagnosed by routines called by this routine.
3) If tabnam contains any nonprintable characters, the error
is diagnosed by routines called by this routine.
4) If ncols is non-positive or greater than the maximum allowed
number SPICE_EK_MXCLSG, the error SPICE(INVALIDCOUNT) is
signaled.
5) If any column name exceeds SPICE_EK_CNAMSZ characters in
length, the error is diagnosed by routines called by this
routine.
6) If any column name contains non-printable characters, the
error is diagnosed by routines called by this routine.
7) If a declaration cannot be understood by this routine, the
error is diagnosed by routines called by this routine.
8) If an non-positive string length or element size is specified,
the error is diagnosed by routines called by this routine.
9) If an I/O error occurs while reading or writing the indicated
file, the error will be diagnosed by routines called by this
routine.
10) If the input string pointer for the table name is null, the
error SPICE(NULLPOINTER) will be signaled.
12) If the input tablen name string has length zero, the error
SPICE(EMPTYSTRING) will be signaled.
13) If the string pointer for cnames is null, the error
SPICE(NULLPOINTER) will be signaled.
14) If the string length cnmlen is less than 2, the error
SPICE(STRINGTOOSHORT) will be signaled.
15) If the string pointer for decls is null, the error
SPICE(NULLPOINTER) will be signaled.
16) If the string length declen is less than 2, the error
SPICE(STRINGTOOSHORT) will be signaled.
-Files
See the EK Required Reading for a discussion of the EK file
format.
-Particulars
This routine operates by side effects: it prepares an EK for
the addition of a new segment. It is not necessary to take
any special action to `complete' a segment; segments are readable
after the completion of any record insertion, deletion, write,
or update operation.
-Examples
1) Suppose we have an E-kernel named ORDER_DB.EK which contains
records of orders for data products. The E-kernel has a
table called DATAORDERS that consists of the set of columns
listed below:
DATAORDERS
Column Name Data Type
----------- ---------
ORDER_ID INTEGER
CUSTOMER_ID INTEGER
LAST_NAME CHARACTER*(*)
FIRST_NAME CHARACTER*(*)
ORDER_DATE TIME
COST DOUBLE PRECISION
The order database also has a table of items that have been
ordered. The columns of this table are shown below:
DATAITEMS
Column Name Data Type
----------- ---------
ITEM_ID INTEGER
ORDER_ID INTEGER
ITEM_NAME CHARACTER*(*)
DESCRIPTION CHARACTER*(*)
PRICE DOUBLE PRECISION
We'll suppose that the file ORDER_DB.EK contains two segments,
the first containing the DATAORDERS table and the second
containing the DATAITEMS table.
Below, we show how we'd open a new EK file and start the
first of the segments described above.
#include "SpiceUsr.h"
#include <stdio.h>
void main()
{
/.
Constants
./
#define CNMLEN SPICE_EK_CSTRLN
#define DECLEN 201
#define EKNAME "order_db.ek"
#define FNMLEN 50
#define IFNAME "Test EK/Created 20-SEP-1995"
#define LNMLEN 50
#define LSK "leapseconds.ker"
#define NCOLS 6
#define NRESVC 0
#define TABLE "DATAORDERS"
#define TNMLEN CSPICE_EK_TAB_NAM_LEN
#define UTCLEN 30
/.
Local variables
./
SpiceBoolean nlflgs [ NROWS ];
SpiceChar cdecls [ NCOLS ] [ DECLEN ];
SpiceChar cnames [ NCOLS ] [ CNMLEN ];
SpiceChar fnames [ NROWS ] [ FNMLEN ];
SpiceChar lnames [ NROWS ] [ LNMLEN ];
SpiceChar dateStr [ UTCLEN ];
SpiceDouble costs [ NROWS ];
SpiceDouble ets [ NROWS ];
SpiceInt cstids [ NROWS ];
SpiceInt ordids [ NROWS ];
SpiceInt handle;
SpiceInt i;
SpiceInt segno;
SpiceInt sizes [ NROWS ];
/.
Load a leapseconds kernel for UTC/ET conversion.
./
furnsh_c ( LSK );
/.
Open a new EK file. For simplicity, we will not
reserve any space for the comment area, so the
number of reserved comment characters is zero.
The constant IFNAME is the internal file name.
./
ekopn_c ( EKNAME, IFNAME, NRESVC, &handle );
/.
Set up the table and column names and declarations
for the DATAORDERS segment. We'll index all of
the columns. All columns are scalar, so we omit
the size declaration. Only the COST column may take
null values.
./
strcpy ( cnames[0], "ORDER_ID" );
strcpy ( cdecls[0], "DATATYPE = INTEGER, INDEXED = TRUE" );
strcpy ( cnames[1], "CUSTOMER_ID" );
strcpy ( cdecls[1], "DATATYPE = INTEGER, INDEXED = TRUE" );
strcpy ( cnames[2], "LAST_NAME" );
strcpy ( cdecls[2], "DATATYPE = CHARACTER*(*),"
"INDEXED = TRUE" );
strcpy ( cnames[3], "FIRST_NAME" );
strcpy ( cdecls[3], "DATATYPE = CHARACTER*(*),"
"INDEXED = TRUE" );
strcpy ( cnames[4], "ORDER_DATE" );
strcpy ( cdecls[4], "DATATYPE = TIME, INDEXED = TRUE" );
strcpy ( cnames[5], "COST" );
strcpy ( cdecls[5], "DATATYPE = DOUBLE PRECISION,"
"INDEXED = TRUE,"
"NULLS_OK = TRUE" );
/.
Start the segment.
./
ekbseg_c ( handle, TABLE, NCOLS, CNMLEN,
cnames, DECLEN, cdecls, &segno );
/.
Add data to the segment. No special action
is required to finish the segment.
./
[Data are added via calls to ekappr_c and the
ekacec_c, ekaced_c, and ekacei_c routines. See any
of these routines for examples.]
/.
At this point, the second segment could be
created by an analogous process. In fact, the
second segment could be created at any time; it is
not necessary to populate the first segment with
data before starting the second segment.
./
/.
The file must be closed by a call to ekcls_c.
./
ekcls_c ( handle );
}
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
-Version
-CSPICE Version 1.1.0, 12-JUL-2002 (NJB)
Call to C2F_CreateStrArr_Sig replaced with call to C2F_MapStrArr.
-CSPICE Version 1.0.0, 17-NOV-2001 (NJB)
-Index_Entries
start new E-kernel segment
start new EK segment
-&
*/
{ /* Begin ekbseg_c */
/*
Local variables
*/
SpiceChar * fCnameArr;
SpiceChar * fCdeclArr;
SpiceInt fCnameLen;
SpiceInt fCdeclLen;
/*
Participate in error tracing.
*/
chkin_c ( "ekbseg_c" );
/*
Check the table name to make sure the pointer is non-null
and the string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "ekbseg_c", tabnam );
/*
Check the column name array to make sure the pointer is non-null
and the string length is non-zero. Note: this check is normally
done for output strings: CHKOSTR is the macro that does the job.
*/
CHKOSTR ( CHK_STANDARD, "ekbseg_c", cnames, cnmlen );
/*
Check the declaration array to make sure the pointer is non-null
and the string length is non-zero.
*/
CHKOSTR ( CHK_STANDARD, "ekbseg_c", decls, declen );
C2F_MapStrArr ( "ekbseg_c",
ncols, cnmlen, cnames, &fCnameLen, &fCnameArr );
if ( failed_c() )
{
chkout_c ( "ekbseg_c" );
return;
}
C2F_MapStrArr ( "ekbseg_c",
ncols, declen, decls, &fCdeclLen, &fCdeclArr );
if ( failed_c() )
{
free ( fCnameArr );
chkout_c ( "ekbseg_c" );
return;
}
/*
Call the f2c'd Fortran routine. Use explicit type casts for every
type defined by f2c.
*/
ekbseg_ ( ( integer * ) &handle,
( char * ) tabnam,
( integer * ) &ncols,
( char * ) fCnameArr,
( char * ) fCdeclArr,
( integer * ) segno,
( ftnlen ) strlen(tabnam),
( ftnlen ) fCnameLen,
( ftnlen ) fCdeclLen );
/*
Clean up all of our dynamically allocated arrays.
*/
free ( fCnameArr );
free ( fCdeclArr );
/*
Map segno to C style range.
*/
(*segno)--;
chkout_c ( "ekbseg_c" );
} /* End ekbseg_c */
void gfuds_c ( void ( * udfunc ) ( SpiceDouble et,
SpiceDouble * value ),
void ( * udqdec ) ( void ( * udfunc )
( SpiceDouble et,
SpiceDouble * value ),
SpiceDouble et,
SpiceBoolean * isdecr ),
ConstSpiceChar * relate,
SpiceDouble refval,
SpiceDouble adjust,
SpiceDouble step,
SpiceInt nintvls,
SpiceCell * cnfine,
SpiceCell * result )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
udfunc I Name of the routine that computes the scalar value
of interest at some time.
udqdec I Name of the routine that computes whether the
current state is decreasing.
relate I Operator that either looks for an extreme value
(max, min, local, absolute) or compares the
geometric quantity value and a number.
refval I Value used as reference for geometric quantity
condition.
adjust I Allowed variation for absolute extremal
geometric conditions.
step I Step size used for locating extrema and roots.
nintvls I Workspace window interval count
cnfine I-O SPICE window to which the search is restricted.
result O SPICE window containing results.
-Detailed_Input
udfunc the name of the external routine that returns the
value of the scalar quantity of interest at time ET.
The calling sequence for "udfunc" is:
udfunc ( et, &value )
where:
et an input double precision value
representing the TDB ephemeris seconds time
at which to determine the scalar value.
value is the value of the geometric quantity
at 'et'.
udqdec the name of the external routine that determines if
the scalar quantity calculated by "udfunc" is decreasing.
The calling sequence:
udqdec ( et, &isdecr )
where:
et an input double precision value representing
the TDB ephemeris seconds time at at which
to determine the time derivative of 'udfunc'.
isdecr a logical variable indicating whether
or not the scalar value returned by udfunc
is decreasing. 'isdecr' returns true if the
time derivative of "udfunc" at 'et' is negative.
relate the scalar string comparison operator indicating
the numeric constraint of interest. Values are:
">" value of scalar quantity greater than some
reference (refval).
"=" value of scalar quantity equal to some
reference (refval).
"<" value of scalar quantity less than some
reference (refval).
"ABSMAX" The scalar quantity is at an absolute
maximum.
"ABSMIN" The scalar quantity is at an absolute
minimum.
"LOCMAX" The scalar quantity is at a local
maximum.
"LOCMIN" The scalar quantity is at a local
minimum.
The caller may indicate that the region of interest
is the set of time intervals where the quantity is
within a specified distance of an absolute extremum.
The argument 'adjust' (described below) is used to
specified this distance.
Local extrema are considered to exist only in the
interiors of the intervals comprising the confinement
window: a local extremum cannot exist at a boundary
point of the confinement window.
relate is insensitive to case, leading and
trailing blanks.
refval is the reference value used to define an equality or
inequality to satisfied by the scalar quantity.
The units of refval are those of the scalar quantity.
adjust the amount by which the quantity is allowed to vary
from an absolute extremum.
If the search is for an absolute minimum is performed,
the resulting window contains time intervals when the
geometric quantity value has values between ABSMIN and
ABSMIN + adjust.
If the search is for an absolute maximum, the
corresponding range is between ABSMAX - adjust and
ABSMAX.
'adjust' is not used for searches for local extrema,
equality or inequality conditions and must have value
zero for such searches.
step the double precision time step size to use in
the search.
'step' must be short enough to for a search using this
step size to locate the time intervals where the
scalar quantity function is monotone increasing or
decreasing. However, 'step' must not be *too* short,
or the search will take an
The choice of 'step' affects the completeness but not
the precision of solutions found by this routine; the
precision is controlled by the convergence tolerance.
See the discussion of the parameter SPICE_GF_CNVTOL for
details.
'step' has units of TDB seconds.
nintvls an integer value specifying the number of intervals in the
the internal workspace array used by this routine. 'nintvls'
should be at least as large as the number of intervals
within the search region on which the specified observer-target
vector coordinate function is monotone increasing or decreasing.
It does no harm to pick a value of 'nintvls' larger than the
minimum required to execute the specified search, but if chosen
too small, the search will fail.
cnfine a double precision SPICE window that confines the time
period over which the specified search is conducted.
cnfine may consist of a single interval or a collection
of intervals.
In some cases the confinement window can be used to
greatly reduce the time period that must be searched
for the desired solution. See the Particulars section
below for further discussion.
See the Examples section below for a code example
that shows how to create a confinement window.
-Detailed_Output
cnfine is the input confinement window, updated if necessary
so the control area of its data array indicates the
window's size and cardinality. The window data are
unchanged.
result is a SPICE window representing the set of time
intervals, within the confinement period, when the
specified geometric event occurs.
If `result' is non-empty on input, its contents
will be discarded before gfuds_c conducts its
search.
-Parameters
None.
-Exceptions
1) In order for this routine to produce correct results,
the step size must be appropriate for the problem at hand.
Step sizes that are too large may cause this routine to miss
roots; step sizes that are too small may cause this routine
to run unacceptably slowly and in some cases, find spurious
roots.
This routine does not diagnose invalid step sizes, except
that if the step size is non-positive, an error is signaled
by a routine in the call tree of this routine.
2) Due to numerical errors, in particular,
- Truncation error in time values
- Finite tolerance value
- Errors in computed geometric quantities
it is *normal* for the condition of interest to not always be
satisfied near the endpoints of the intervals comprising the
result window.
The result window may need to be contracted slightly by the
caller to achieve desired results. The SPICE window routine
wncond_c can be used to contract the result window.
3) If an error (typically cell overflow) occurs while performing
window arithmetic, the error will be diagnosed by a routine
in the call tree of this routine.
4) If the relational operator `relate' is not recognized, an
error is signaled by a routine in the call tree of this
routine.
5) If 'adjust' is negative, the error SPICE(VALUEOUTOFRANGE) will
signal from a routine in the call tree of this routine.
A non-zero value for 'adjust' when 'relate' has any value other than
"ABSMIN" or "ABSMAX" causes the error SPICE(INVALIDVALUE) to
signal from a routine in the call tree of this routine.
6) If required ephemerides or other kernel data are not
available, an error is signaled by a routine in the call tree
of this routine.
7) If the workspace interval count is less than 1, the error
SPICE(VALUEOUTOFRANGE) will be signaled.
8) If the required amount of workspace memory cannot be
allocated, the error SPICE(MALLOCFAILURE) will be
signaled.
9) If any input string argument pointer is null, the error
SPICE(NULLPOINTER) will be signaled.
10) If any input string argument is empty, the error
SPICE(EMPTYSTRING) will be signaled.
11) If either input cell has type other than SpiceDouble,
the error SPICE(TYPEMISMATCH) is signaled.
-Files
Appropriate kernels must be loaded by the calling program before
this routine is called.
If the scalar function requires access to ephemeris data:
- SPK data: ephemeris data for any body over the
time period defined by the confinement window must be
loaded. If aberration corrections are used, the states of
target and observer relative to the solar system barycenter
must be calculable from the available ephemeris data.
Typically ephemeris data are made available by loading one
or more SPK files via furnsh_c.
- If non-inertial reference frames are used, then PCK
files, frame kernels, C-kernels, and SCLK kernels may be
needed.
In all cases, kernel data are normally loaded once per program
run, NOT every time this routine is called.
-Particulars
This routine provides a simpler, but less flexible interface
than does the routine zzgfrel_ for conducting searches for events
corresponding to an arbitrary user defined scalar quantity
function. Applications that require support for progress
reporting, interrupt handling, non-default step or refinement
functions, or non-default convergence tolerance should call
zzgfrel_ rather than this routine.
This routine determines a set of one or more time intervals
within the confinement window when the scalar function
satisfies a caller-specified constraint. The resulting set of
intervals is returned as a SPICE window.
udqdec Default Template
=======================
The user must supply a routine to determine whether sign of the
time derivative of udfunc is positive or negative at 'et'. For
cases where udfunc is numerically well behaved, the user
may find it convenient to use a routine based on the below
template. uddc_c determines the truth of the expression
d (udfunc)
-- < 0
dt
using the library routine uddf_c to numerically calculate the
derivative of udfunc using a three-point estimation. Use
of gfdecr requires only changing the "udfunc" argument
to that of the user provided scalar function passed to gfuds_c
and defining the differential interval size, 'dt'. Please see
the Examples section for an example of gfdecr use.
void gfdecr ( SpiceDouble et, SpiceBoolean * isdecr )
{
SpiceDouble dt = h, double precision interval size;
uddc_c( udfunc, uddf_c, et, dt, isdecr );
return;
}
Below we discuss in greater detail aspects of this routine's
solution process that are relevant to correct and efficient
use of this routine in user applications.
The Search Process
==================
Regardless of the type of constraint selected by the caller, this
routine starts the search for solutions by determining the time
periods, within the confinement window, over which the specified
scalar function is monotone increasing and monotone
decreasing. Each of these time periods is represented by a SPICE
window. Having found these windows, all of the quantity
function's local extrema within the confinement window are known.
Absolute extrema then can be found very easily.
Within any interval of these "monotone" windows, there will be at
most one solution of any equality constraint. Since the boundary
of the solution set for any inequality constraint is the set
of points where an equality constraint is met, the solutions of
both equality and inequality constraints can be found easily
once the monotone windows have been found.
Step Size
=========
The monotone windows (described above) are found using a two-step
search process. Each interval of the confinement window is
searched as follows: first, the input step size is used to
determine the time separation at which the sign of the rate of
change of quantity function will be sampled. Starting at
the left endpoint of an interval, samples will be taken at each
step. If a change of sign is found, a root has been bracketed; at
that point, the time at which the time derivative of the quantity
function is zero can be found by a refinement process, for
example, using a binary search.
Note that the optimal choice of step size depends on the lengths
of the intervals over which the quantity function is monotone:
the step size should be shorter than the shortest of these
intervals (within the confinement window).
The optimal step size is *not* necessarily related to the lengths
of the intervals comprising the result window. For example, if
the shortest monotone interval has length 10 days, and if the
shortest result window interval has length 5 minutes, a step size
of 9.9 days is still adequate to find all of the intervals in the
result window. In situations like this, the technique of using
monotone windows yields a dramatic efficiency improvement over a
state-based search that simply tests at each step whether the
specified constraint is satisfied. The latter type of search can
miss solution intervals if the step size is shorter than the
shortest solution interval.
Having some knowledge of the relative geometry of the targets and
observer can be a valuable aid in picking a reasonable step size.
In general, the user can compensate for lack of such knowledge by
picking a very short step size; the cost is increased computation
time.
Note that the step size is not related to the precision with which
the endpoints of the intervals of the result window are computed.
That precision level is controlled by the convergence tolerance.
Convergence Tolerance
=====================
Once a root has been bracketed, a refinement process is used to
narrow down the time interval within which the root must lie.
This refinement process terminates when the location of the root
has been determined to within an error margin called the
"convergence tolerance." The convergence tolerance used by this
routine is set via the parameter SPICE_GF_CNVTOL.
The value of SPICE_GF_CNVTOL is set to a "tight" value so that the
tolerance doesn't become the limiting factor in the accuracy of
solutions found by this routine. In general the accuracy of input
data will be the limiting factor.
Making the tolerance tighter than SPICE_GF_CNVTOL is unlikely to
be useful, since the results are unlikely to be more accurate.
Making the tolerance looser will speed up searches somewhat,
since a few convergence steps will be omitted. However, in most
cases, the step size is likely to have a much greater affect
on processing time than would the convergence tolerance.
The Confinement Window
======================
The simplest use of the confinement window is to specify a time
interval within which a solution is sought. However, the
confinement window can, in some cases, be used to make searches
more efficient. Sometimes it's possible to do an efficient search
to reduce the size of the time period over which a relatively
slow search of interest must be performed.
-Examples
The numerical results shown for these examples may differ across
platforms. The results depend on the SPICE kernels used as
input, the compiler and supporting libraries, and the machine
specific arithmetic implementation.
Conduct a search on the range-rate of the vector from the Sun
to the Moon. Define a function to calculate the value.
Use the meta-kernel shown below to load the required SPICE
kernels.
KPL/MK
File name: standard.tm
This meta-kernel is intended to support operation of SPICE
example programs. The kernels shown here should not be
assumed to contain adequate or correct versions of data
required by SPICE-based user applications.
In order for an application to use this meta-kernel, the
kernels referenced here must be present in the user's
current working directory.
\begindata
KERNELS_TO_LOAD = ( 'de414.bsp',
'pck00008.tpc',
'naif0009.tls' )
\begintext
Code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "SpiceUsr.h"
#include "SpiceZfc.h"
#include "SpiceZad.h"
#define MAXWIN 20000
#define TIMFMT "YYYY-MON-DD HR:MN:SC.###"
#define TIMLEN 41
#define NLOOPS 7
void gfq ( SpiceDouble et, SpiceDouble * value );
void gfdecrx ( void ( * udfunc ) ( SpiceDouble et,
SpiceDouble * value ),
SpiceDouble et,
SpiceBoolean * isdecr );
doublereal dvnorm_(doublereal *state);
int main( int argc, char **argv )
{
/.
Create the needed windows. Note, one interval
consists of two values, so the total number
of cell values to allocate is twice
the number of intervals.
./
SPICEDOUBLE_CELL ( result, 2*MAXWIN );
SPICEDOUBLE_CELL ( cnfine, 2 );
SpiceDouble begtim;
SpiceDouble endtim;
SpiceDouble step;
SpiceDouble adjust;
SpiceDouble refval;
SpiceDouble beg;
SpiceDouble end;
SpiceChar begstr [ TIMLEN ];
SpiceChar endstr [ TIMLEN ];
SpiceInt count;
SpiceInt i;
SpiceInt j;
ConstSpiceChar * relate [NLOOPS] = { "=",
"<",
">",
"LOCMIN",
"ABSMIN",
"LOCMAX",
"ABSMAX"
};
printf( "Compile date %s, %s\n\n", __DATE__, __TIME__ );
/.
Load kernels.
./
furnsh_c( "standard.tm" );
/.
Store the time bounds of our search interval in the 'cnfine'
confinement window.
./
str2et_c( "2007 JAN 01", &begtim );
str2et_c( "2007 APR 01", &endtim );
wninsd_c ( begtim, endtim, &cnfine );
/.
Search using a step size of 1 day (in units of seconds). The reference
value is .3365 km/s. We're not using the adjustment feature, so
we set 'adjust' to zero.
./
step = spd_c();
adjust = 0.;
refval = .3365;
for ( j = 0; j < NLOOPS; j++ )
{
printf ( "Relation condition: %s \n", relate[j] );
/.
Perform the search. The SPICE window 'result' contains
the set of times when the condition is met.
./
gfuds_c ( gfq,
gfdecrx,
relate[j],
refval,
adjust,
step,
MAXWIN,
&cnfine,
&result );
count = wncard_c( &result );
/.
Display the results.
./
if (count == 0 )
{
printf ( "Result window is empty.\n\n" );
}
else
{
for ( i = 0; i < count; i++ )
{
/.
Fetch the endpoints of the Ith interval
of the result window.
./
wnfetd_c ( &result, i, &beg, &end );
timout_c ( beg, TIMFMT, TIMLEN, begstr );
timout_c ( end, TIMFMT, TIMLEN, endstr );
printf ( "Start time, drdt = %s \n", begstr );
printf ( "Stop time, drdt = %s \n", endstr );
}
}
printf("\n");
}
kclear_c();
return( 0 );
}
/.
The user defined functions required by GFUDS.
gfq for udfunc
gfdecr for udqdec
./
/.
-Procedure Procedure gfq
./
void gfq ( SpiceDouble et, SpiceDouble * value )
/.
-Abstract
User defined geometric quantity function. In this case,
the range from the sun to the Moon at TDB time 'et'.
./
{
/. Initialization ./
SpiceInt targ = 301;
SpiceInt obs = 10;
SpiceChar * ref = "J2000";
SpiceChar * abcorr = "NONE";
SpiceDouble state [6];
SpiceDouble lt;
/.
Retrieve the vector from the Sun to the Moon in the J2000
frame, without aberration correction.
./
spkez_c ( targ, et, ref, abcorr, obs, state, < );
/.
Calculate the scalar range rate corresponding the
'state' vector.
./
*value = dvnorm_( state );
return;
}
/.
-Procedure gfdecrx
./
void gfdecrx ( void ( * udfunc ) ( SpiceDouble et,
SpiceDouble * value ),
SpiceDouble et,
SpiceBoolean * isdecr )
/.
-Abstract
User defined function to detect if the function derivative
is negative (the function is decreasing) at TDB time 'et'.
./
{
SpiceDouble dt = 10.;
/.
Determine if "udfunc" is decreasing at 'et'.
uddc_c - the GF function to determine if
the derivative of the user defined
function is negative at 'et'.
uddf_c - the SPICE function to numerically calculate the
derivative of 'udfunc' at 'et' for the
interval [et-dt, et+dt].
./
uddc_c( udfunc, et, dt, isdecr );
return;
}
The program outputs:
Relation condition: =
Start time, drdt = 2007-JAN-02 00:35:19.574
Stop time, drdt = 2007-JAN-02 00:35:19.574
Start time, drdt = 2007-JAN-19 22:04:54.899
Stop time, drdt = 2007-JAN-19 22:04:54.899
Start time, drdt = 2007-FEB-01 23:30:13.428
Stop time, drdt = 2007-FEB-01 23:30:13.428
Start time, drdt = 2007-FEB-17 11:10:46.540
Stop time, drdt = 2007-FEB-17 11:10:46.540
Start time, drdt = 2007-MAR-04 15:50:19.929
Stop time, drdt = 2007-MAR-04 15:50:19.929
Start time, drdt = 2007-MAR-18 09:59:05.959
Stop time, drdt = 2007-MAR-18 09:59:05.959
Relation condition: <
Start time, drdt = 2007-JAN-02 00:35:19.574
Stop time, drdt = 2007-JAN-19 22:04:54.899
Start time, drdt = 2007-FEB-01 23:30:13.428
Stop time, drdt = 2007-FEB-17 11:10:46.540
Start time, drdt = 2007-MAR-04 15:50:19.929
Stop time, drdt = 2007-MAR-18 09:59:05.959
Relation condition: >
Start time, drdt = 2007-JAN-01 00:00:00.000
Stop time, drdt = 2007-JAN-02 00:35:19.574
Start time, drdt = 2007-JAN-19 22:04:54.899
Stop time, drdt = 2007-FEB-01 23:30:13.428
Start time, drdt = 2007-FEB-17 11:10:46.540
Stop time, drdt = 2007-MAR-04 15:50:19.929
Start time, drdt = 2007-MAR-18 09:59:05.959
Stop time, drdt = 2007-APR-01 00:00:00.000
Relation condition: LOCMIN
Start time, drdt = 2007-JAN-11 07:03:58.988
Stop time, drdt = 2007-JAN-11 07:03:58.988
Start time, drdt = 2007-FEB-10 06:26:15.439
Stop time, drdt = 2007-FEB-10 06:26:15.439
Start time, drdt = 2007-MAR-12 03:28:36.404
Stop time, drdt = 2007-MAR-12 03:28:36.404
Relation condition: ABSMIN
Start time, drdt = 2007-JAN-11 07:03:58.988
Stop time, drdt = 2007-JAN-11 07:03:58.988
Relation condition: LOCMAX
Start time, drdt = 2007-JAN-26 02:27:33.766
Stop time, drdt = 2007-JAN-26 02:27:33.766
Start time, drdt = 2007-FEB-24 09:35:07.816
Stop time, drdt = 2007-FEB-24 09:35:07.816
Start time, drdt = 2007-MAR-25 17:26:56.150
Stop time, drdt = 2007-MAR-25 17:26:56.150
Relation condition: ABSMAX
Start time, drdt = 2007-MAR-25 17:26:56.150
Stop time, drdt = 2007-MAR-25 17:26:56.150
-Restrictions
1) Any kernel files required by this routine must be loaded
before this routine is called.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
E.D. Wright (JPL)
-Version
-CSPICE Version 1.0.0, 22-FEB-2010 (EDW)
-Index_Entries
GF user defined scalar function search
-&
*/
{ /* Begin gfuds_c */
/*
Local variables
*/
doublereal * work;
static SpiceInt nw = SPICE_GF_NWMAX;
SpiceInt nBytes;
/*
Participate in error tracing.
*/
if ( return_c() )
{
return;
}
chkin_c ( "gfuds_c" );
/*
Make sure cell data types are d.p.
*/
CELLTYPECHK2 ( CHK_STANDARD, "gfuds_c", SPICE_DP, cnfine, result );
/*
Initialize the input cells if necessary.
*/
CELLINIT2 ( cnfine, result );
/*
Check the other input strings to make sure each pointer is non-null
and each string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "gfuds_c", relate );
/*
Store the input function pointers so these functions can be
called by the GF adapters.
*/
zzadsave_c ( UDFUNC, (void *)(udfunc) );
zzadsave_c ( UDQDEC, (void *)(udqdec) );
/*
Check the workspace size; some mallocs have a violent
dislike for negative allocation amounts. To be safe,
rule out a count of zero intervals as well.
*/
if ( nintvls < 1 )
{
setmsg_c ( "The specified workspace interval count # was "
"less than the minimum allowed value of one (1)." );
errint_c ( "#", nintvls );
sigerr_c ( "SPICE(VALUEOUTOFRANGE)" );
chkout_c ( "gfuds_c" );
return;
}
/*
Allocate the workspace. 'nintvls' indicates the maximum number of
intervals returned in 'result'. An interval consists of
two values.
*/
nintvls = 2 * nintvls;
nBytes = (nintvls + SPICE_CELL_CTRLSZ ) * nw * sizeof(SpiceDouble);
work = (doublereal *) alloc_SpiceMemory( nBytes );
if ( !work )
{
setmsg_c ( "Workspace allocation of # bytes failed due to "
"malloc failure" );
errint_c ( "#", nBytes );
sigerr_c ( "SPICE(MALLOCFAILED)" );
chkout_c ( "gfuds_c" );
return;
}
/*
Let the f2c'd routine do the work.
We pass the adapter functions, not those provided as inputs,
to the f2c'd routine:
zzadfunc_c adapter for udfunc
zzadqdec_c '' udqdec
*/
(void) gfuds_( ( U_fp ) zzadfunc_c,
( U_fp ) zzadqdec_c,
( char * ) relate,
( doublereal * ) &refval,
( doublereal * ) &adjust,
( doublereal * ) &step,
( doublereal * ) (cnfine->base),
( integer * ) &nintvls,
( integer * ) &nw,
( doublereal * ) work,
( doublereal * ) (result->base),
( ftnlen ) strlen(relate) );
/*
Always free dynamically allocated memory.
*/
free_SpiceMemory( work );
/*
Sync the output cell.
*/
if ( !failed_c() )
{
zzsynccl_c ( F2C, result );
}
ALLOC_CHECK;
chkout_c ( "gfuds_c" );
} /* End gfuds_c */
void pxform_c ( ConstSpiceChar * from,
ConstSpiceChar * to,
SpiceDouble et,
SpiceDouble rotate[3][3] )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
from I Name of the frame to transform from.
to I Name of the frame to transform to.
et I Epoch of the rotation matrix.
rotate O A rotation matrix.
-Detailed_Input
from is the name of a reference frame in which a position
vector is known.
to is the name of a reference frame in which it is desired
to represent a position vector.
et is the epoch in ephemeris seconds past the epoch of
J2000 (TDB) at which the position transformation matrix
`rotate' should be evaluated.
-Detailed_Output
rotate is the matrix that transforms position vectors from the
reference frame `from' to the frame `to' at epoch `et'.
If (x, y, z) is a position relative to the frame `from'
then the vector ( x', y', z') is the same position
relative to the frame `to' at epoch `et'. Here the
vector ( x', y', z' ) is defined by the equation:
- - - - - -
| x' | | | | x |
| y' | = | rotate | | y |
| z' | | | | z |
- - - - - -
-Parameters
None.
-Exceptions
1) If sufficient information has not been supplied via loaded SPICE
kernels to compute the transformation between the two frames, the
error will be diagnosed by a routine in the call tree of this
routine.
2) If either frame `from' or `to' is not recognized the error
SPICE(UNKNOWNFRAME) will be signaled.
-Files
None.
-Particulars
This routine provides the user level interface to computing
position transformations from one reference frame to another.
Note that the reference frames may be inertial or non-inertial.
However, the user must take care that sufficient SPICE kernel
information is loaded to provide a complete position
transformation path from the from frame to the to frame.
-Examples
Suppose that you have geodetic coordinates of a station on the
surface of the earth and that you need the inertial (J2000)
position of this station. The following code fragment
illustrates how to transform the position of the station to a
J2000 position.
#include "SpiceUsr.h"
.
.
.
bodvcd_c ( 399, radii, 3, &n, abc );
equatr = abc[0];
polar = abc[2];
f = ( equatr - polar ) / equatr;
georec_c ( long, lat, 0.0, equatr, f, epos );
pxform_c ( "IAU_EARTH", "J2000", et, rotate );
mxv_c ( rotate, epos, jpos );
The position jpos is the desired J2000 position of the station.
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
C.H. Acton (JPL)
N.J. Bachman (JPL)
B.V. Semenov (JPL)
W.L. Taber (JPL)
-Version
-CSPICE Version 1.0.4, 27-FEB-2008 (BVS)
Added FRAMES to the Required_Reading section of the header.
-CSPICE Version 1.0.3, 24-OCT-2005 (NJB)
Header updates: example had invalid flattening factor
computation; this was corrected. Reference to bodvar_c was
replaced with reference to bodvcd_c.
-CSPICE Version 1.0.2, 07-JAN-2004 (EDW)
Trivial typo correction to example section.
-CSPICE Version 1.0.1, 29-JUL-2003 (NJB) (CHA)
Various header corrections were made.
-CSPICE Version 1.0.0, 20-JUN-1999 (NJB) (WLT)
-Index_Entries
Find a position transformation matrix
-&
*/
{ /* Begin pxform_c */
/*
Participate in error tracing.
*/
chkin_c ( "pxform_c" );
/*
Check the input strings to make sure the pointers are non-null
and the string lengths are non-zero.
*/
CHKFSTR ( CHK_STANDARD, "pxform_c", from );
CHKFSTR ( CHK_STANDARD, "pxform_c", to );
/*
Call the f2c'd routine.
*/
pxform_ ( ( char * ) from,
( char * ) to,
( doublereal * ) &et,
( doublereal * ) rotate,
( ftnlen ) strlen(from),
( ftnlen ) strlen(to) );
/*
Transpose the output to obtain row-major order.
*/
xpose_c ( rotate, rotate );
chkout_c ( "pxform_c" );
} /* End pxform_c */
void ckcov_c ( ConstSpiceChar * ck,
SpiceInt idcode,
SpiceBoolean needav,
ConstSpiceChar * level,
SpiceDouble tol,
ConstSpiceChar * timsys,
SpiceCell * cover )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
ck I Name of CK file.
idcode I ID code of object.
needav I Flag indicating whether angular velocity is needed.
level I Coverage level: "SEGMENT" OR "INTERVAL".
tol I Tolerance in ticks.
timsys I Time system used to represent coverage.
cover I/O Window giving coverage for `idcode'.
-Detailed_Input
ck is the name of a C-kernel.
idcode is the integer ID code of an object, normally a
spacecraft structure or instrument, for which
pointing data are expected to exist in the specified
CK file.
needav is a logical variable indicating whether only
segments having angular velocity are to be considered
when determining coverage. When `needav' is
SPICETRUE, segments without angular velocity don't
contribute to the coverage window; when `needav' is
SPICEFALSE, all segments for `idcode' may contribute
to the coverage window.
level is the level (granularity) at which the coverage
is examined. Allowed values and corresponding
meanings are:
"SEGMENT" The output coverage window contains
intervals defined by the start and
stop times of segments for the object
designated by `idcode'.
"INTERVAL" The output coverage window contains
interpolation intervals of segments
for the object designated by
`idcode'. For type 1 segments, which
don't have interpolation intervals,
each epoch associated with a pointing
instance is treated as a singleton
interval; these intervals are added
to the coverage window.
All interpolation intervals are
considered to lie within the segment
bounds for the purpose of this
summary: if an interpolation
interval extends beyond the segment
coverage interval, only its
intersection with the segment
coverage interval is considered to
contribute to the total coverage.
tol is a tolerance value expressed in ticks of the
spacecraft clock associated with IDCODE. Before each
interval is inserted into the coverage window, the
interval is intersected with the segment coverage
interval, then if the intersection is non-empty, it
is expanded by `tol': the left endpoint of the
intersection interval is reduced by `tol' and the
right endpoint is increased by `tol'. Adjusted
interval endpoints, when expressed as encoded SCLK,
never are less than zero ticks. Any intervals that
overlap as a result of the expansion are merged.
The coverage window returned when tol > 0 indicates
the coverage provided by the file to the CK readers
ckgpav_c and ckgp_c when that value of `tol' is
passed to them as an input.
timsys is a string indicating the time system used in the
output coverage window. `timsys' may have the
values:
"SCLK" Elements of `cover' are expressed in
encoded SCLK ("ticks"), where the
clock is associated with the object
designated by `idcode'.
"TDB" Elements of `cover' are expressed as
seconds past J2000 TDB.
cover is an initialized CSPICE window data structure.
`cover' optionally may contain coverage data on
input; on output, the data already present in `cover'
will be combined with coverage found for the object
designated by `idcode' in the file `ck'.
If `cover' contains no data on input, its size and
cardinality still must be initialized.
-Detailed_Output
cover is a CSPICE window data structure which represents
the merged coverage for `idcode'. When the coverage
level is "INTERVAL", this is the set of time
intervals for which data for `idcode' are present in
the file `ck', merged with the set of time intervals
present in `cover' on input. The merged coverage is
represented as the union of one or more disjoint time
intervals. The window `cover' contains the pairs of
endpoints of these intervals.
When the coverage level is "SEGMENT", `cover' is
computed in a manner similar to that described above,
but the coverage intervals used in the computation
are those of segments rather than interpolation
intervals within segments.
When `tol' is > 0, the intervals comprising the
coverage window for `idcode' are expanded by `tol'
and any intervals overlapping as a result are merged.
The resulting window is returned in `cover'. The
expanded window in no case extends beyond the segment
bounds in either direction by more than `tol'.
The interval endpoints contained in `cover' are
encoded spacecraft clock times if `timsys' is "SCLK";
otherwise the times are converted from encoded
spacecraft clock to seconds past J2000 TDB.
See the Examples section below for a complete example
program showing how to retrieve the endpoints from
`cover'.
-Parameters
None.
-Exceptions
1) If the input file has transfer format, the error
SPICE(INVALIDFORMAT) is signaled.
2) If the input file is not a transfer file but has architecture
other than DAF, the error SPICE(BADARCHTYPE) is signaled.
3) If the input file is a binary DAF file of type other than
CK, the error SPICE(BADFILETYPE) is signaled.
4) If the CK file cannot be opened or read, the error will
be diagnosed by routines called by this routine. The output
window will not be modified.
5) If the size of the output window argument `cover' is
insufficient to contain the actual number of intervals in the
coverage window for `idcode', the error will be diagnosed by
routines called by this routine.
6) If `tol' is negative, the error SPICE(VALUEOUTOFRANGE) is
signaled.
7) If `level' is not recognized, the error SPICE(INVALIDOPTION)
is signaled.
8) If `timsys' is not recognized, the error SPICE(INVALIDOPTION)
is signaled.
9) If a time conversion error occurs, the error will be
diagnosed by a routine in the call tree of this routine.
10) If the output time system is TDB, the CK subsystem must be
able to map `idcode' to the ID code of the associated
spacecraft clock. If this mapping cannot be performed, the
error will be diagnosed by a routine in the call tree of this
routine.
11) The error SPICE(EMPTYSTRING) is signaled if any of the input
strings `ck', `level', or `timsys' do not contain at least one
character, since such an input string cannot be converted to a
Fortran-style string in this case.
12) The error SPICE(NULLPOINTER) is signaled if the if any of the input
strings `ck', `level', or `timsys' are null.
-Files
This routine reads a C-kernel.
If the output time system is "TDB", then a leapseconds kernel
and an SCLK kernel for the spacecraft clock associated with
`idcode' must be loaded before this routine is called.
If the ID code of the clock associated with `idcode' is not
equal to
idcode / 1000
then the kernel variable
CK_<idcode>_SCLK
must be present in the kernel pool to identify the clock
associated with `idcode'. This variable must contain the ID code
to be used for conversion between SCLK and TDB. Normally this
variable is provided in a text kernel loaded via furnsh_c.
-Particulars
This routine provides an API via which applications can determine
the coverage a specified CK file provides for a specified
object.
-Examples
1) Display the interval-level coverage for each object in a
specified CK file. Use tolerance of zero ticks. Do not request
angular velocity. Express the results in the TDB time system.
Find the set of objects in the file. Loop over the contents of
the ID code set: find the coverage for each item in the set and
display the coverage.
#include <stdio.h>
#include "SpiceUsr.h"
int main()
{
/.
Local parameters
./
#define FILSIZ 256
#define MAXIV 100000
#define WINSIZ ( 2 * MAXIV )
#define TIMLEN 51
#define MAXOBJ 1000
/.
Local variables
./
SPICEDOUBLE_CELL ( cover, WINSIZ );
SPICEINT_CELL ( ids, MAXOBJ );
SpiceChar ck [ FILSIZ ];
SpiceChar lsk [ FILSIZ ];
SpiceChar sclk [ FILSIZ ];
SpiceChar timstr [ TIMLEN ];
SpiceDouble b;
SpiceDouble e;
SpiceInt i;
SpiceInt j;
SpiceInt niv;
SpiceInt obj;
/.
Load a leapseconds kernel and SCLK kernel for output time
conversion. Note that we assume a single spacecraft clock is
associated with all of the objects in the CK.
./
prompt_c ( "Name of leapseconds kernel > ", FILSIZ, lsk );
furnsh_c ( lsk );
prompt_c ( "Name of SCLK kernel > ", FILSIZ, sclk );
furnsh_c ( sclk );
/.
Get name of CK file.
./
prompt_c ( "Name of CK file > ", FILSIZ, ck );
/.
Find the set of objects in the CK file.
./
ckobj_c ( ck, &ids );
/.
We want to display the coverage for each object. Loop over
the contents of the ID code set, find the coverage for
each item in the set, and display the coverage.
./
for ( i = 0; i < card_c( &ids ); i++ )
{
/.
Find the coverage window for the current object.
Empty the coverage window each time so we don't
include data for the previous object.
./
obj = SPICE_CELL_ELEM_I( &ids, i );
scard_c ( 0, &cover );
ckcov_c ( ck, obj, SPICEFALSE,
"INTERVAL", 0.0, "TDB", &cover );
/.
Get the number of intervals in the coverage window.
./
niv = wncard_c( &cover );
/.
Display a simple banner.
./
printf ( "%s\n", "========================================" );
printf ( "Coverage for object %ld\n", obj );
/.
Convert the coverage interval start and stop times to TDB
calendar strings.
./
for ( j = 0; j < niv; j++ )
{
/.
Get the endpoints of the jth interval.
./
wnfetd_c ( &cover, j, &b, &e );
/.
Convert the endpoints to TDB calendar
format time strings and display them.
./
timout_c ( b,
"YYYY MON DD HR:MN:SC.###### (TDB) ::TDB",
TIMLEN,
timstr );
printf ( "\n"
"Interval: %ld\n"
"Start: %s\n",
j,
timstr );
timout_c ( e,
"YYYY MON DD HR:MN:SC.###### (TDB) ::TDB",
TIMLEN,
timstr );
printf ( "Stop: %s\n", timstr );
}
printf ( "%s\n", "========================================" );
}
return ( 0 );
}
2) Find the segment-level coverage for the object designated by
IDCODE provided by the set of CK files loaded via a metakernel.
(The metakernel must also specify leapseconds and SCLK kernels.)
Use tolerance of zero ticks. Do not request angular velocity.
Express the results in the TDB time system.
#include <stdio.h>
#include "SpiceUsr.h"
int main()
{
/.
Local parameters
./
#define FILSIZ 256
#define LNSIZE 81
#define MAXCOV 100000
#define WINSIZ ( 2 * MAXCOV )
#define TIMLEN 51
/.
Local variables
./
SPICEDOUBLE_CELL ( cover, WINSIZ );
SpiceBoolean found;
SpiceChar file [ FILSIZ ];
SpiceChar idch [ LNSIZE ];
SpiceChar meta [ FILSIZ ];
SpiceChar source [ FILSIZ ];
SpiceChar timstr [ TIMLEN ];
SpiceChar type [ LNSIZE ];
SpiceDouble b;
SpiceDouble e;
SpiceInt count;
SpiceInt handle;
SpiceInt i;
SpiceInt idcode;
SpiceInt niv;
/.
Prompt for the metakernel name; load the metakernel.
The metakernel lists the CK files whose coverage
for `idcode' we'd like to determine. The metakernel
must also specify a leapseconds kernel and an SCLK
kernel for the clock associated with `idcode'.
./
prompt_c ( "Name of metakernel > ", FILSIZ, meta );
furnsh_c ( meta );
/.
Get the ID code of interest.
./
prompt_c ( "Enter ID code > ", LNSIZE, idch );
prsint_c ( idch, &idcode );
/.
Find out how many kernels are loaded. Loop over the
kernels: for each loaded CK file, add its coverage
for `idcode', if any, to the coverage window.
./
ktotal_c ( "CK", &count );
for ( i = 0; i < count; i++ )
{
kdata_c ( i, "CK", FILSIZ,
LNSIZE, FILSIZ, file,
type, source, &handle, &found );
ckcov_c ( file, idcode, SPICEFALSE,
"SEGMENT", 0.0, "TDB", &cover );
}
/.
Display results.
Get the number of intervals in the coverage window.
./
niv = wncard_c( &cover );
/.
Display a simple banner.
./
printf ( "\nCoverage for object %ld\n", idcode );
/.
Convert the coverage interval start and stop times to TDB
calendar strings.
./
for ( i = 0; i < niv; i++ )
{
/.
Get the endpoints of the ith interval.
./
wnfetd_c ( &cover, i, &b, &e );
/.
Convert the endpoints to TDB calendar
format time strings and display them.
./
timout_c ( b,
"YYYY MON DD HR:MN:SC.###### (TDB) ::TDB",
TIMLEN,
timstr );
printf ( "\n"
"Interval: %ld\n"
"Start: %s\n",
i,
timstr );
timout_c ( e,
"YYYY MON DD HR:MN:SC.###### (TDB) ::TDB",
TIMLEN,
timstr );
printf ( "Stop: %s\n", timstr );
}
return ( 0 );
}
-Restrictions
1) When this routine is used to accumulate coverage for `idcode'
provided by multiple CK files, the inputs `needav', `level', `tol',
and `timsys' must have the same values for all files in order
for the result to be meaningful.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
-Version
-CSPICE Version 1.0.1, 30-NOV-2007 (NJB)
Corrected bug in first example program in header:
program now empties result window prior to collecting
data for each object. Updated examples to use wncard_c
rather than card_c. Updated second example to demonstrate
segment-level summary capability.
-CSPICE Version 1.0.0, 07-JAN-2005 (NJB)
-Index_Entries
get coverage window for ck object
-&
*/
{ /* Begin ckcov_c */
/*
Local variables
*/
logical need;
/*
Participate in error tracing.
*/
if ( return_c() )
{
return;
}
chkin_c ( "ckcov_c" );
/*
Check the input string `ck' to make sure the pointer is non-null
and the string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "ckcov_c", ck );
/*
Check the input string `level' to make sure the pointer is non-null
and the string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "ckcov_c", level );
/*
Check the input string `timsys' to make sure the pointer is non-null
and the string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "ckcov_c", timsys );
/*
Make sure cell data type is d.p.
*/
CELLTYPECHK ( CHK_STANDARD, "ckcov_c", SPICE_DP, cover );
/*
Initialize the cell if necessary.
*/
CELLINIT ( cover );
/*
Call the f2c'd Fortran routine.
*/
need = needav;
ckcov_ ( ( char * ) ck,
( integer * ) &idcode,
( logical * ) &need,
( char * ) level,
( doublereal * ) &tol,
( char * ) timsys,
( doublereal * ) (cover->base),
( ftnlen ) strlen(ck),
( ftnlen ) strlen(level),
( ftnlen ) strlen(timsys) );
/*
Sync the output cell.
*/
if ( !failed_c() )
{
zzsynccl_c ( F2C, cover );
}
chkout_c ( "ckcov_c" );
} /* End ckcov_c */
void spkw18_c ( SpiceInt handle,
SpiceSPK18Subtype subtyp,
SpiceInt body,
SpiceInt center,
ConstSpiceChar * frame,
SpiceDouble first,
SpiceDouble last,
ConstSpiceChar * segid,
SpiceInt degree,
SpiceInt n,
const void * packts,
ConstSpiceDouble epochs[] )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
handle I Handle of an SPK file open for writing.
subtyp I SPK type 18 subtype code.
body I NAIF code for an ephemeris object.
center I NAIF code for center of motion of body.
frame I Reference frame name.
first I Start time of interval covered by segment.
last I End time of interval covered by segment.
segid I Segment identifier.
degree I Degree of interpolating polynomials.
n I Number of states.
states I Array of states.
epochs I Array of epochs corresponding to states.
MAXDEG P Maximum allowed degree of interpolating polynomial.
-Detailed_Input
handle is the file handle of an SPK file that has been
opened for writing.
subtyp is an integer code indicating the subtype of the
the segment to be created.
body is the NAIF integer code for an ephemeris object
whose state relative to another body is described
by the segment to be created.
center is the NAIF integer code for the center of motion
of the object identified by body.
frame is the NAIF name for a reference frame
relative to which the state information for body
is specified.
first,
last are, respectively, the start and stop times of
the time interval over which the segment defines
the state of body.
segid is the segment identifier. An SPK segment
identifier may contain up to 40 characters.
degree is the nominal degree of the polynomials used to
interpolate the states contained in the input
packets. All components of the state vectors are
interpolated by polynomials of the specified
degree, except near the segment boundaries,
or if the total number of states in the segment
is too few to allow interpolation using the
specified degree.
n is the number of packets in the input packet
array.
packts contains a time-ordered array of data packets
representing geometric states of body relative
to center, specified relative to frame. The
packet structure depends on the segment subtype
as follows:
Type 0 (indicated by code S18TP0):
x, y, z, dx/dt, dy/dt, dz/dt,
vx, vy, vz, dvx/dt, dvy/dt, dvz/dt
where x, y, z represent Cartesian position
components and vx, vy, vz represent Cartesian
velocity components. Note well: vx, vy, and
vz *are not necessarily equal* to the time
derivatives of x, y, and z. This packet
structure mimics that of the Rosetta/MEX orbit
file from which the data are taken.
Type 1 (indicated by code S18TP1):
x, y, z, dx/dt, dy/dt, dz/dt
where x, y, z represent Cartesian position
components and vx, vy, vz represent Cartesian
velocity components.
Position units are kilometers, velocity units
are kilometers per second, and acceleration units
are kilometers per second per second.
epochs is an array of epochs corresponding to the members
of the packets array. The epochs are specified as
seconds past J2000, TDB.
-Detailed_Output
None. See $Particulars for a description of the effect of this
routine.
-Parameters
MAXDEG is the maximum allowed degree of the interpolating
polynomial. If the value of MAXDEG is increased,
the CSPICE routine spkpvn_ must be changed
accordingly. In particular, the size of the
record passed to SPKRnn and SPKEnn must be
increased, and comments describing the record size
must be changed.
-Exceptions
If any of the following exceptions occur, this routine will return
without creating a new segment.
1) If frame is not a recognized name, the error
SPICE(INVALIDREFFRAME) is signaled.
2) If the last non-blank character of segid occurs past index 40,
the error SPICE(SEGIDTOOLONG) is signaled.
3) If segid contains any nonprintable characters, the error
SPICE(NONPRINTABLECHARS) is signaled.
4) If degree is not at least 1 or is greater than MAXDEG, the
error SPICE(INVALIDDEGREE) is signaled.
5) If the window size implied by DEGREE is odd, the error
SPICE(INVALIDDEGREE) is signaled.
6) If the number of packets n is not at least 1,
the error SPICE(TOOFEWSTATES) will be signaled.
7) If first is greater than or equal to last then the error
SPICE(BADDESCRTIMES) will be signaled.
8) If the elements of the array epochs are not in strictly
increasing order, the error SPICE(TIMESOUTOFORDER) will be
signaled.
9) If the first epoch epochs[0] is greater than first, the error
SPICE(BADDESCRTIMES) will be signaled.
10) If the last epoch epochs[n-1] is less than last, the error
SPICE(BADDESCRTIMES) will be signaled.
11) If either the input frame or segment ID string pointer is null,
the error SPICE(NULLPOINTER) is signaled.
12) If either the input frame or segment ID string is empty,
the error SPICE(EMPTYSTRING) is signaled.
-Files
A new type 18 SPK segment is written to the SPK file attached
to HANDLE.
-Particulars
This routine writes an SPK type 18 data segment to the open SPK
file according to the format described in the type 18 section of
the SPK Required Reading. The SPK file must have been opened with
write access.
-Examples
Suppose that you have states and are prepared to produce
a segment of type 18 in an SPK file.
The following code fragment could be used to add the new segment
to a previously opened SPK file attached to handle. The file must
have been opened with write access.
#include "SpiceUsr.h"
.
.
.
/.
Create a segment identifier.
./
#define SEGID "MY_SAMPLE_SPK_TYPE_18_SEGMENT"
/.
Write the segment.
./
spkw18_c ( handle, subtyp, body, center,
frame, first, last, segid,
degree, n, states, epochs );
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
-Version
-CSPICE Version 1.0.1, 29-APR-2003 (NJB)
Description of error condition arising from invalid window
size was corrected.
-CSPICE Version 1.0.0, 16-AUG-2002 (NJB)
-Index_Entries
write spk type_18 ephemeris data segment
-&
*/
{ /* Begin spkw18_c */
/*
Local variables
*/
SpiceInt locSubtype;
/*
Participate in error tracing.
*/
if ( return_c() )
{
return;
}
chkin_c ( "spkw18_c" );
/*
Check the input strings to make sure the pointers
are non-null and the string lengths are non-zero.
*/
CHKFSTR ( CHK_STANDARD, "spkw18_c", frame );
CHKFSTR ( CHK_STANDARD, "spkw18_c", segid );
locSubtype = (SpiceInt) subtyp;
/*
Write the segment.
*/
spkw18_ ( ( integer * ) &handle,
( integer * ) &locSubtype,
( integer * ) &body,
( integer * ) ¢er,
( char * ) frame,
( doublereal * ) &first,
( doublereal * ) &last,
( char * ) segid,
( integer * ) °ree,
( integer * ) &n,
( doublereal * ) packts,
( doublereal * ) epochs,
( ftnlen ) strlen(frame),
( ftnlen ) strlen(segid) );
chkout_c ( "spkw18_c" );
} /* End spkw18_c */
void spkw09_c ( SpiceInt handle,
SpiceInt body,
SpiceInt center,
ConstSpiceChar * frame,
SpiceDouble first,
SpiceDouble last,
ConstSpiceChar * segid,
SpiceInt degree,
SpiceInt n,
ConstSpiceDouble states[][6],
ConstSpiceDouble epochs[] )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
handle I Handle of an SPK file open for writing.
body I NAIF code for an ephemeris object.
center I NAIF code for center of motion of body.
frame I Reference frame name.
first I Start time of interval covered by segment.
last I End time of interval covered by segment.
segid I Segment identifier.
degree I Degree of interpolating polynomials.
n I Number of states.
states I Array of states.
epochs I Array of epochs corresponding to states.
maxdeg P Maximum allowed degree of interpolating polynomial.
-Detailed_Input
handle is the file handle of an SPK file that has been
opened for writing.
body is the NAIF integer code for an ephemeris object
whose state relative to another body is described
by the segment to be created.
center is the NAIF integer code for the center of motion
of the object identified by body.
frame is the NAIF name for a reference frame
relative to which the state information for body
is specified.
first,
last are, respectively, the start and stop times of
the time interval over which the segment defines
the state of body.
segid is the segment identifier. An SPK segment
identifier may contain up to 40 characters.
degree is the degree of the Lagrange polynomials used to
interpolate the states. All components of the
state vectors are interpolated by polynomials of
fixed degree.
n is the number of states in the input state vector
array.
states contains a time-ordered array of geometric states
( x, y, z, dx/dt, dy/dt, dz/dt, in kilometers and
kilometers per second ) of body relative to center,
specified relative to frame.
epochs is an array of epochs corresponding to the members
of the state array. The epochs are specified as
seconds past J2000, TDB.
-Detailed_Output
None. See $Particulars for a description of the effect of this
routine.
-Parameters
MAXDEG is the maximum allowed degree of the interpolating
polynomial. If the value of MAXDEG is increased,
the CSPICE routine spkpvn_ must be changed
accordingly. In particular, the size of the
record passed to spkrNN_ and spkeNN_ must be
increased, and comments describing the record size
must be changed.
The current value of MAXDEG is 15.
-Exceptions
If any of the following exceptions occur, this routine will return
without creating a new segment.
1) If frame is not a recognized name, the error
SPICE(INVALIDREFFRAME) is signaled.
2) If the last non-blank character of segid occurs past index 40,
the error SPICE(SEGIDTOOLONG) is signaled.
3) If segid contains any nonprintable characters, the error
SPICE(NONPRINTABLECHARS) is signaled.
4) If degree is not at least 1 or is greater than MAXDEG, the
error SPICE(INVALIDDEGREE) is signaled.
5) If the number of states n is not at least degree+1, the error
SPICE(TOOFEWSTATES) will be signaled.
6) If first is greater than or equal to last then the error
SPICE(BADDESCRTIMES) will be signaled.
7) If the elements of the array epochs are not in strictly
increasing order, the error SPICE(TIMESOUTOFORDER) will be
signaled.
8) If the first epoch epochs[0] is greater than first, the error
SPICE(BADDESCRTIMES) will be signaled.
9) If the last epoch epochs[n] is less than last, the error
SPICE(BADDESCRTIMES) will be signaled.
10) If either the input frame or segment ID string pointer is null,
the error SPICE(NULLPOINTER) is signaled.
11) If either the input frame or segment ID string is empty,
the error SPICE(EMPTYSTRING) is signaled.
-Files
A new type 9 SPK segment is written to the SPK file attached
to handle.
-Particulars
This routine writes an SPK type 09 data segment to the open SPK
file according to the format described in the type 09 section of
the SPK Required Reading. The SPK file must have been opened with
write access.
-Examples
Suppose that you have states and are prepared to produce
a segment of type 09 in an SPK file.
The following code fragment could be used to add the new segment
to a previously opened SPK file attached to HANDLE. The file must
have been opened with write access.
#include "SpiceUsr.h"
.
.
.
/.
Create a segment identifier.
./
#define SEGID "MY_SAMPLE_SPK_TYPE_9_SEGMENT"
/.
Write the segment.
./
spkw09_c ( handle, body, center, frame,
first, last, segid, degree,
n, states, epochs );
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
K.R. Gehringer (JPL)
N.J. Bachman (JPL)
J.M. Lynch (JPL)
W.L. Taber (JPL)
-Version
-CSPICE Version 1.0.0, 21-JUN-1999 (KRG) (NJB) (JML) (WLT)
-Index_Entries
write spk type_9 ephemeris data segment
-&
*/
{ /* Begin spkw09_c */
/*
Participate in error tracing.
*/
chkin_c ( "spkw09_c" );
/*
Check the input strings to make sure the pointers
are non-null and the string lengths are non-zero.
*/
CHKFSTR ( CHK_STANDARD, "spkw09_c", frame );
CHKFSTR ( CHK_STANDARD, "spkw09_c", segid );
/*
Write the segment.
*/
spkw09_ ( ( integer * ) &handle,
( integer * ) &body,
( integer * ) ¢er,
( char * ) frame,
( doublereal * ) &first,
( doublereal * ) &last,
( char * ) segid,
( integer * ) °ree,
( integer * ) &n,
( doublereal * ) states,
( doublereal * ) epochs,
( ftnlen ) strlen(frame),
( ftnlen ) strlen(segid) );
chkout_c ( "spkw09_c" );
} /* End spkw09_c */
void tpictr_c ( ConstSpiceChar * sample,
SpiceInt lenout,
SpiceInt lenerr,
SpiceChar * pictur,
SpiceBoolean * ok,
SpiceChar * errmsg )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
sample I A sample time string.
lenout I The length for the output picture string.
lenerr I The length for the output error string.
pictur O A format picture that describes sample.
ok O Flag indicating whether sample parsed successfully.
errmsg O Diagnostic returned if sample cannot be parsed.
-Detailed_Input
sample is a representative time string to use as a model to
format time strings.
lenout is the allowed length for the output picture. This length
must large enough to hold the output string plus the null
terminator. If the output string is expected to have x
characters, lenout needs to be x + 1. 80 is a reasonable
value for lenout (79 characters plus the null
terminator).
lenerr is the allowed length for the output error string.
-Detailed_Output
pictur is a format picture suitable for use with the SPICE
routine timout_c. This picture, when used to format an
epoch via timout_c, will yield the same time components in
the same order as the components in sample.
ok is a logical flag indicating whether the input format
sample could be parsed. If all of the components of
sample are recognizable, ok will be returned with the
value SPICEFALSE. If some part of pictur cannot be
parsed, ok will be returned with the value SPICEFALSE.
errmsg is a diagnostic message that indicates what part of
sample was not recognizable. If sample was successfully
parsed, ok will be SPICEFALSE and errmsg will be
returned as an empty string.
-Parameters
None.
-Files
None.
-Exceptions
Error free.
1) All problems with the inputs are diagnosed via ok and errmsg.
2) If a format picture can not be created from the sample
time string, pictur is returned as a blank string.
-Particulars
Although the routine timout_c provides CSPICE users with a great
deal of flexibility in formatting time strings, users must
master the means by which a time picture is constructed
suitable for use by timout_c.
This routine allows CSPICE users to supply a sample time string
from which a corresponding time format picture can be created,
freeing users from the task of mastering the intricacies of
the routine timout_c.
Note that timout_c can produce many time strings whose patterns
can not be discerned by this routine. When such outputs are
called for, the user must consult timout_c and construct the
appropriate format picture "by hand." However, these exceptional
formats are not widely used and are not generally recognizable
to an uninitiated reader.
-Examples
Suppose you need to print epochs corresponding to some events and
you wish the epochs to have the same arrangement of components as in
the string "10:23 P.M. PDT January 3, 1993".
The following subroutine call will construct the appropriate format
picture for use with timout_c.
tpictr_c ( "10:23 P.M. PDT January 3, 1993",
lenout, lenerr, pictur, &ok, errmsg );
The resulting picture is:
"AP:MN AMPM PDT Month DD, YYYY ::UTC-7"
This picture can be used with timout_c to format a sequence
of epochs, et[0],...,et[n-1] (given as ephemeris seconds past J2000)
as shown in the loop below:
#include "SpiceUsr.h"
.
.
.
for ( i = 0; i < n; i++ )
{
timout_c ( et[i], pictur, string );
printf ( "Epoch: %d --- %s\n", i, string );
}
-Restrictions
None.
-Author_and_Institution
W.L. Taber (JPL)
E.D. Wright (JPL)
-Literature_References
None.
-Version
-CSPICE Version 1.0.0, 23-JUL-1999 (EDW) (WLT)
-Index_Entries
Use a sample time string to produce a time format picture
-&
*/
{ /* Begin tpictr_c */
/*
Local variables
*/
logical okeydoke;
/*
Participate in error tracing.
*/
chkin_c ( "tpictr_c" );
/*
Check the input string sample to make sure the pointer is non-null
and the string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "tpictr_c", sample );
/*
Make sure the output strings have at least enough room for one output
character and a null terminator. Also check for a null pointer.
*/
CHKOSTR ( CHK_STANDARD, "tpictr_c", pictur, lenout );
CHKOSTR ( CHK_STANDARD, "tpictr_c", errmsg, lenerr );
/*
Call the f2c'd routine.
*/
tpictr_( ( char * ) sample,
( char * ) pictur,
( logical * ) &okeydoke,
( char * ) errmsg,
( ftnlen ) strlen( sample ),
( ftnlen ) lenout - 1,
( ftnlen ) lenerr - 1 );
/*
Convert the output strings to C style.
*/
F2C_ConvertStr( lenout, pictur );
F2C_ConvertStr( lenerr, errmsg );
/*
Convert the status flag from logical to SpiceBoolean.
*/
*ok = okeydoke;
chkout_c ( "tpictr_c" );
} /* End tpictr_c */
void drdpgr_c ( ConstSpiceChar * body,
SpiceDouble lon,
SpiceDouble lat,
SpiceDouble alt,
SpiceDouble re,
SpiceDouble f,
SpiceDouble jacobi[3][3] )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
body I Name of body with which coordinates are associated.
lon I Planetographic longitude of a point (radians).
lat I Planetographic latitude of a point (radians).
alt I Altitude of a point above reference spheroid.
re I Equatorial radius of the reference spheroid.
f I Flattening coefficient.
jacobi O Matrix of partial derivatives.
-Detailed_Input
body Name of the body with which the planetographic
coordinate system is associated.
`body' is used by this routine to look up from the
kernel pool the prime meridian rate coefficient giving
the body's spin sense. See the Files and Particulars
header sections below for details.
lon Planetographic longitude of the input point. This is
the angle between the prime meridian and the meridian
containing the input point. For bodies having
prograde (aka direct) rotation, the direction of
increasing longitude is positive west: from the +X
axis of the rectangular coordinate system toward the
-Y axis. For bodies having retrograde rotation, the
direction of increasing longitude is positive east:
from the +X axis toward the +Y axis.
The earth, moon, and sun are exceptions:
planetographic longitude is measured positive east for
these bodies.
The default interpretation of longitude by this
and the other planetographic coordinate conversion
routines can be overridden; see the discussion in
Particulars below for details.
Longitude is measured in radians. On input, the range
of longitude is unrestricted.
lat Planetographic latitude of the input point. For a
point P on the reference spheroid, this is the angle
between the XY plane and the outward normal vector at
P. For a point P not on the reference spheroid, the
planetographic latitude is that of the closest point
to P on the spheroid.
Latitude is measured in radians. On input, the
range of latitude is unrestricted.
alt Altitude of point above the reference spheroid.
Units of `alt' must match those of `re'.
re Equatorial radius of a reference spheroid. This
spheroid is a volume of revolution: its horizontal
cross sections are circular. The shape of the
spheroid is defined by an equatorial radius `re' and
a polar radius `rp'. Units of `re' must match those of
`alt'.
f Flattening coefficient =
(re-rp) / re
where `rp' is the polar radius of the spheroid, and the
units of `rp' match those of `re'.
-Detailed_Output
JACOBI is the matrix of partial derivatives of the conversion
from planetographic to rectangular coordinates. It
has the form
.- -.
| DX/DLON DX/DLAT DX/DALT |
| DY/DLON DY/DLAT DY/DALT |
| DZ/DLON DZ/DLAT DZ/DALT |
`- -'
evaluated at the input values of `lon', `lat' and `alt'.
-Parameters
None.
-Exceptions
1) If the body name `body' cannot be mapped to a NAIF ID code,
and if `body' is not a string representation of an integer,
the error SPICE(IDCODENOTFOUND) will be signaled.
2) If the kernel variable
BODY<ID code>_PGR_POSITIVE_LON
is present in the kernel pool but has a value other
than one of
'EAST'
'WEST'
the error SPICE(INVALIDOPTION) will be signaled. Case
and blanks are ignored when these values are interpreted.
3) If polynomial coefficients for the prime meridian of `body'
are not available in the kernel pool, and if the kernel
variable BODY<ID code>_PGR_POSITIVE_LON is not present in
the kernel pool, the error SPICE(MISSINGDATA) will be signaled.
4) If the equatorial radius is non-positive, the error
SPICE(VALUEOUTOFRANGE) is signaled.
5) If the flattening coefficient is greater than or equal to one,
the error SPICE(VALUEOUTOFRANGE) is signaled.
6) The error SPICE(EMPTYSTRING) is signaled if the input
string `body' does not contain at least one character, since the
input string cannot be converted to a Fortran-style string in
this case.
7) The error SPICE(NULLPOINTER) is signaled if the input string
pointer `body' is null.
-Files
This routine expects a kernel variable giving body's prime
meridian angle as a function of time to be available in the
kernel pool. Normally this item is provided by loading a PCK
file. The required kernel variable is named
BODY<body ID>_PM
where <body ID> represents a string containing the NAIF integer
ID code for `body'. For example, if `body' is "JUPITER", then
the name of the kernel variable containing the prime meridian
angle coefficients is
BODY599_PM
See the PCK Required Reading for details concerning the prime
meridian kernel variable.
The optional kernel variable
BODY<body ID>_PGR_POSITIVE_LON
also is normally defined via loading a text kernel. When this
variable is present in the kernel pool, the prime meridian
coefficients for `body' are not required by this routine. See the
Particulars section below for details.
-Particulars
It is often convenient to describe the motion of an object in the
planetographic coordinate system. However, when performing
vector computations it's hard to beat rectangular coordinates.
To transform states given with respect to planetographic
coordinates to states with respect to rectangular coordinates,
one makes use of the Jacobian of the transformation between the
two systems.
Given a state in planetographic coordinates
( lon, lat, alt, dlon, dlat, dalt )
the velocity in rectangular coordinates is given by the matrix
equation:
t | t
(dx, dy, dz) = jacobi| * (dlon, dlat, dalt)
|(lon,lat,alt)
This routine computes the matrix
|
jacobi|
|(lon,lat,alt)
In the planetographic coordinate system, longitude is defined
using the spin sense of the body. Longitude is positive to the
west if the spin is prograde and positive to the east if the spin
is retrograde. The spin sense is given by the sign of the first
degree term of the time-dependent polynomial for the body's prime
meridian Euler angle "W": the spin is retrograde if this term is
negative and prograde otherwise. For the sun, planets, most
natural satellites, and selected asteroids, the polynomial
expression for W may be found in a SPICE PCK kernel.
The earth, moon, and sun are exceptions: planetographic longitude
is measured positive east for these bodies.
If you wish to override the default sense of positive longitude
for a particular body, you can do so by defining the kernel
variable
BODY<body ID>_PGR_POSITIVE_LON
where <body ID> represents the NAIF ID code of the body. This
variable may be assigned either of the values
'WEST'
'EAST'
For example, you can have this routine treat the longitude
of the earth as increasing to the west using the kernel
variable assignment
BODY399_PGR_POSITIVE_LON = 'WEST'
Normally such assignments are made by placing them in a text
kernel and loading that kernel via furnsh_c.
The definition of this kernel variable controls the behavior of
the CSPICE planetographic routines
pgrrec_c
recpgr_c
dpgrdr_c
drdpgr_c
It does not affect the other CSPICE coordinate conversion
routines.
-Examples
Numerical results shown for this example may differ between
platforms as the results depend on the SPICE kernels used as
input and the machine specific arithmetic implementation.
Find the planetographic state of the earth as seen from
Mars in the J2000 reference frame at January 1, 2005 TDB.
Map this state back to rectangular coordinates as a check.
#include <stdio.h>
#include "SpiceUsr.h"
int main()
{
/.
Local variables
./
SpiceDouble alt;
SpiceDouble drectn [3];
SpiceDouble et;
SpiceDouble f;
SpiceDouble jacobi [3][3];
SpiceDouble lat;
SpiceDouble lon;
SpiceDouble lt;
SpiceDouble pgrvel [3];
SpiceDouble radii [3];
SpiceDouble re;
SpiceDouble rectan [3];
SpiceDouble rp;
SpiceDouble state [6];
SpiceInt n;
/.
Load a PCK file containing a triaxial
ellipsoidal shape model and orientation
data for Mars.
./
furnsh_c ( "pck00008.tpc" );
/.
Load an SPK file giving ephemerides of earth and Mars.
./
furnsh_c ( "de405.bsp" );
/.
Load a leapseconds kernel to support time conversion.
./
furnsh_c ( "naif0007.tls" );
/.
Look up the radii for Mars. Although we
omit it here, we could first call badkpv_c
to make sure the variable BODY499_RADII
has three elements and numeric data type.
If the variable is not present in the kernel
pool, bodvrd_c will signal an error.
./
bodvrd_c ( "MARS", "RADII", 3, &n, radii );
/.
Compute flattening coefficient.
./
re = radii[0];
rp = radii[2];
f = ( re - rp ) / re;
/.
Look up the geometric state of earth as seen from Mars at
January 1, 2005 TDB, relative to the J2000 reference
frame.
./
str2et_c ( "January 1, 2005 TDB", &et);
spkezr_c ( "Earth", et, "J2000", "LT+S",
"Mars", state, < );
/.
Convert position to planetographic coordinates.
./
recpgr_c ( "mars", state, re, f, &lon, &lat, &alt );
/.
Convert velocity to planetographic coordinates.
./
dpgrdr_c ( "MARS", state[0], state[1], state[2],
re, f, jacobi );
mxv_c ( jacobi, state+3, pgrvel );
/.
As a check, convert the planetographic state back to
rectangular coordinates.
./
pgrrec_c ( "mars", lon, lat, alt, re, f, rectan );
drdpgr_c ( "mars", lon, lat, alt, re, f, jacobi );
mxv_c ( jacobi, pgrvel, drectn );
printf ( "\n"
"Rectangular coordinates:\n"
"\n"
" X (km) = %18.9e\n"
" Y (km) = %18.9e\n"
" Z (km) = %18.9e\n"
"\n"
"Rectangular velocity:\n"
"\n"
" dX/dt (km/s) = %18.9e\n"
" dY/dt (km/s) = %18.9e\n"
" dZ/dt (km/s) = %18.9e\n"
"\n"
"Ellipsoid shape parameters:\n"
"\n"
" Equatorial radius (km) = %18.9e\n"
" Polar radius (km) = %18.9e\n"
" Flattening coefficient = %18.9e\n"
"\n"
"Planetographic coordinates:\n"
"\n"
" Longitude (deg) = %18.9e\n"
" Latitude (deg) = %18.9e\n"
" Altitude (km) = %18.9e\n"
"\n"
"Planetographic velocity:\n"
"\n"
" d Longitude/dt (deg/s) = %18.9e\n"
" d Latitude/dt (deg/s) = %18.9e\n"
" d Altitude/dt (km/s) = %18.9e\n"
"\n"
"Rectangular coordinates from inverse mapping:\n"
"\n"
" X (km) = %18.9e\n"
" Y (km) = %18.9e\n"
" Z (km) = %18.9e\n"
"\n"
"Rectangular velocity from inverse mapping:\n"
"\n"
" dX/dt (km/s) = %18.9e\n"
" dY/dt (km/s) = %18.9e\n"
" dZ/dt (km/s) = %18.9e\n"
"\n",
state [0],
state [1],
state [2],
state [3],
state [4],
state [5],
re,
rp,
f,
lon / rpd_c(),
lat / rpd_c(),
alt,
pgrvel[0]/rpd_c(),
pgrvel[1]/rpd_c(),
pgrvel[2],
rectan [0],
rectan [1],
rectan [2],
drectn [0],
drectn [1],
drectn [2] );
return ( 0 );
}
Output from this program should be similar to the following
(rounding and formatting differ across platforms):
Rectangular coordinates:
X (km) = 1.460397325e+08
Y (km) = 2.785466068e+08
Z (km) = 1.197503153e+08
Rectangular velocity:
dX/dt (km/s) = -4.704288238e+01
dY/dt (km/s) = 9.070217780e+00
dZ/dt (km/s) = 4.756562739e+00
Ellipsoid shape parameters:
Equatorial radius (km) = 3.396190000e+03
Polar radius (km) = 3.376200000e+03
Flattening coefficient = 5.886007556e-03
Planetographic coordinates:
Longitude (deg) = 2.976676591e+02
Latitude (deg) = 2.084450403e+01
Altitude (km) = 3.365318254e+08
Planetographic velocity:
d Longitude/dt (deg/s) = -8.357386316e-06
d Latitude/dt (deg/s) = 1.593493548e-06
d Altitude/dt (km/s) = -1.121443268e+01
Rectangular coordinates from inverse mapping:
X (km) = 1.460397325e+08
Y (km) = 2.785466068e+08
Z (km) = 1.197503153e+08
Rectangular velocity from inverse mapping:
dX/dt (km/s) = -4.704288238e+01
dY/dt (km/s) = 9.070217780e+00
dZ/dt (km/s) = 4.756562739e+00
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
W.L. Taber (JPL)
-Version
-CSPICE Version 1.0.0, 26-DEC-2004 (NJB) (WLT)
-Index_Entries
Jacobian of rectangular w.r.t. planetographic coordinates
-&
*/
{ /* Begin drdpgr_c */
/*
Participate in error tracing.
*/
if ( return_c() )
{
return;
}
chkin_c ( "drdpgr_c" );
/*
Check the input string body to make sure the pointer is non-null
and the string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "drdpgr_c", body );
/*
Call the f2c'd Fortran routine.
*/
drdpgr_ ( ( char * ) body,
( doublereal * ) &lon,
( doublereal * ) &lat,
( doublereal * ) &alt,
( doublereal * ) &re,
( doublereal * ) &f,
( doublereal * ) jacobi,
( ftnlen ) strlen(body) );
/*
Convert Jacobian matrix to row-major order.
*/
xpose_c ( jacobi, jacobi );
chkout_c ( "drdpgr_c" );
} /* End drdpgr_c */
void gcpool_c ( ConstSpiceChar * name,
SpiceInt start,
SpiceInt room,
SpiceInt lenout,
SpiceInt * n,
void * cvals,
SpiceBoolean * found )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
name I Name of the variable whose value is to be returned.
start I Which component to start retrieving for name
room I The largest number of values to return.
lenout I The length of the output string.
n O Number of values returned for name.
cvals O Values associated with name.
found O True if variable is in pool.
-Detailed_Input
name is the name of the variable whose values are to be
returned. If the variable is not in the pool with
character type, found will be SPICEFALSE.
start is the index of the first component of name to return.
The index follows the C convention of being 0 based.
If start is less than 0, it will be treated as 0. If
start is greater than the total number of components
available for name, no values will be returned (n will
be set to zero). However, found will still be set to
SPICETRUE
room is the maximum number of components that should be
returned for this variable. (Usually it is the amount
of room available in the array cvals). If room is
less than 1 the error SPICE(BADARRAYSIZE) will be
signaled.
lenout The allowed length of the output string. This length
must large enough to hold the output string plus the
terminator. If the output string is expected to have x
characters, lenout needs to be x + 1.
-Detailed_Output
n is the number of values associated with name that
are returned. It will always be less than or equal
to room.
If name is not in the pool with character type, no
value is given to n.
cvals is the array of values associated with name.
If name is not in the pool with character type, no
values are given to the elements of cvals.
If the length of cvals is less than the length of
strings stored in the kernel pool (see MAXCHR) the
values returned will be truncated on the right.
found is SPICETRUE if the variable is in the pool and has
character type, SPICEFALSE if it is not.
-Parameters
None.
-Exceptions
1) If the value of room is less than one the error
SPICE(BADARRAYSIZE) is signaled.
2) If cvals has declared length less than the size of a
string to be returned, the value will be truncated on
the right. See MAXCHR in pool.c for the maximum stored size of
string variables.
3) If the input string pointer is null, the error SPICE(NULLPOINTER)
will be signaled.
4) If the input string has length zero, the error SPICE(EMPTYSTRING)
will be signaled.
5) If the output string has length less than two characters, it
is too short to contain one character of output data plus a null
terminator, so it cannot be passed to the underlying Fortran
routine. In this event, the error SPICE(STRINGTOOSHORT) is
signaled.
-Files
None.
-Particulars
This routine provides the user interface to retrieving
character data stored in the kernel pool. This interface
allows you to retrieve the data associated with a variable
in multiple accesses. Under some circumstances this alleviates
the problem of having to know in advance the maximum amount
of space needed to accommodate all kernel variables.
However, this method of access does come with a price. It is
always more efficient to retrieve all of the data associated
with a kernel pool data in one call than it is to retrieve
it in sections.
C requires the length of the output character array to be defined
prior to calling the converted gcpool_c routine. The size of the
cvals output array is user defined and passed as the variable
lenout.
Also see the entry points gdpool_c and gipool_c.
-Examples
The following code fragment demonstrates how the data stored
in a kernel pool variable can be retrieved in pieces. Using the
kernel "test.ker" which contains
\begindata
CTEST_VAL = ('LARRY', 'MOE', 'CURLY' )
ITEST_VAL = ( 3141, 186, 282 )
DTEST_VAL = ( 3.1415, 186. , 282.397 )
The program...
#include <stdio.h>
#include <string.h>
#include "SpiceUsr.h"
#include "SpiceZmc.h"
#define LENOUT 20
#define NUMVALS 2
#define START 1
void main()
{
SpiceInt n;
SpiceChar cvals[NUMVALS][LENOUT];
SpiceBoolean found;
SpiceInt i;
ldpool_c ( "test.ker" );
/.
Get 2 values (NUMVALs) starting at the second value
in the list (START). Each value will be of length LENOUT.
./
gcpool_c ( "CTEST_VAL", START, NUMVALS, LENOUT, &n, cvals,
&found );
for ( i = 0; i < NUMVALS; i++ )
{
printf("%s\n", cvals[i] );
}
exit(0);
}
Will give output of
MOE
CURLY
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
W.L. Taber (JPL)
-Version
-CSPICE Version 2.2.1 07-SEP-2007 (EDW)
Edited the 'lenout' description in the Detailed_Input to
remove the recommendation of 32 as a general use value
for 'lenout'.
-CSPICE Version 2.2.0 18-MAY-2001 (WLT)
Added a cast to (char *) in the call to F2C_ConvertStrArr.
-CSPICE Version 2.1.0 22-JUN-1999 (EDW)
Added local variable to return boolean/logical values. This
fix allows the routine to function if int and long are different
sizes.
-CSPICE Version 2.0.3 09-FEB-1998 (EDW)
Removed the output dynamically allocated string. Conversion
of cval from string to array now accomplished via the
F2C_ConvertStrArray call.
-CSPICE Version 2.0.2 01-FEB-1998 (EDW)
Removed the input and work dynamically allocated strings.
-CSPICE Version 2.0.1 28-JAN-1998 (EDW)
The start parameter is now zero based as per C convention.
Adjusted the amount of memory for the strings to lenout-1.
-CSPICE Version 2.0.0 07-JAN-1998 (EDW)
The routine now function properly for room > 1. Previously
only a single value could be returned.
-CSPICE Version 1.0.0 23-OCT-1997 (EDW)
-Index_Entries
RETURN the character value of a pooled kernel variable
RETURN the string value of a pooled kernel variable
-&
*/
{ /* Begin gcpool_c */
/*
Local variables.
*/
logical yes;
/* The index is zero based here but not in gcpool_. */
start = start + 1;
/*
Participate in error tracing.
*/
chkin_c ( "gcpool_c");
/*
Check the input string utcstr to make sure the pointer is non-null
and the string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "gcpool_c", name );
/*
Make sure the output string has at least enough room for one output
character and a null terminator. Also check for a null pointer.
*/
CHKOSTR ( CHK_STANDARD, "gcpool_c", cvals, lenout );
/*
Call the f2c'd routine
*/
gcpool_( ( char * ) name,
( integer * ) &start,
( integer * ) &room,
( integer * ) n,
( char * ) cvals,
( logical * ) &yes,
( ftnlen ) strlen(name),
( ftnlen ) lenout - 1 );
/* Cast back to a SpiceBoolean. */
*found = yes;
if ( *found )
{
/*
cvals now contains the requested data in a single string
lenout * n long. We need to reform cvals into an array
of n strings each lenout long.
*/
F2C_ConvertTrStrArr ( *n, lenout, (char *)cvals );
}
/* Done. Checkout. */
chkout_c ( "gcpool_c");
} /* End gcpool_c */
void gfrr_c ( ConstSpiceChar * target,
ConstSpiceChar * abcorr,
ConstSpiceChar * obsrvr,
ConstSpiceChar * relate,
SpiceDouble refval,
SpiceDouble adjust,
SpiceDouble step,
SpiceInt nintvls,
SpiceCell * cnfine,
SpiceCell * result )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
SPICE_GF_CNVTOL P Convergence tolerance
target I Name of the target body.
abcorr I Aberration correction flag.
obsrvr I Name of the observing body.
relate I Relational operator.
refval I Reference value.
adjust I Adjustment value for absolute extrema searches.
step I Step size used for locating extrema and roots.
nintvls I Workspace window interval count.
cnfine I-O SPICE window to which the search is confined.
result O SPICE window containing results.
-Detailed_Input
target is the name of a target body. The target body is
an ephemeris object; its trajectory is given by
SPK data.
The string `target' is case-insensitive, and leading
and trailing blanks in `target' are not significant.
Optionally, you may supply a string containing the
integer ID code for the object. For example both
"MOON" and "301" are legitimate strings that indicate
the Moon is the target body.
The target and observer define a position vector which
points from the observer to the target; the time derivative
length of this vector is the "range rate" that serves as
the subject of the search performed by this routine.
abcorr indicates the aberration corrections to be applied to
the observer-target state vector to account for
one-way light time and stellar aberration.
Any aberration correction accepted by the SPICE
routine spkezr_c is accepted here. See the header
of spkezr_c for a detailed description of the
aberration correction options. For convenience,
the options are listed below:
"NONE" Apply no correction.
"LT" "Reception" case: correct for
one-way light time using a Newtonian
formulation.
"LT+S" "Reception" case: correct for
one-way light time and stellar
aberration using a Newtonian
formulation.
"CN" "Reception" case: converged
Newtonian light time correction.
"CN+S" "Reception" case: converged
Newtonian light time and stellar
aberration corrections.
"XLT" "Transmission" case: correct for
one-way light time using a Newtonian
formulation.
"XLT+S" "Transmission" case: correct for
one-way light time and stellar
aberration using a Newtonian
formulation.
"XCN" "Transmission" case: converged
Newtonian light time correction.
"XCN+S" "Transmission" case: converged
Newtonian light time and stellar
aberration corrections.
Case and blanks are not significant in the string
`abcorr'.
obsrvr is the name of the observing body. The observing body is
an ephemeris object; its trajectory is given by SPK
data. `obsrvr' is case-insensitive, and leading and
trailing blanks in `obsrvr' are not significant.
Optionally, you may supply a string containing the
integer ID code for the object. For example both "MOON"
and "301" are legitimate strings that indicate the Moon
is the observer.
relate is a relational operator used to define a constraint
on observer-target range rate. The result window found
by this routine indicates the time intervals where
the constraint is satisfied. Supported values of
`relate' and corresponding meanings are shown below:
">" Distance is greater than the reference
value `refval'.
"=" Distance is equal to the reference
value `refval'.
"<" Distance is less than the reference
value `refval'.
"ABSMAX" Distance is at an absolute maximum.
"ABSMIN" Distance is at an absolute minimum.
"LOCMAX" Distance is at a local maximum.
"LOCMIN" Distance is at a local minimum.
The caller may indicate that the region of interest
is the set of time intervals where the quantity is
within a specified distance of an absolute extremum.
The argument `adjust' (described below) is used to
specify this distance.
Local extrema are considered to exist only in the
interiors of the intervals comprising the confinement
window: a local extremum cannot exist at a boundary
point of the confinement window.
Case is not significant in the string `relate'.
refval is the reference value used together with the argument
`relate' to define an equality or inequality to be
satisfied by the range rate between the specified target
and observer. See the discussion of `relate' above for
further information.
The units of `refval' are km/sec.
adjust is a parameter used to modify searches for absolute
extrema: when `relate' is set to "ABSMAX" or "ABSMIN" and
`adjust' is set to a positive value, gfdist_c will find
times when the observer-target range rate is within
`adjust' km/sec of the specified extreme value.
If `adjust' is non-zero and a search for an absolute
minimum `min' is performed, the result window contains
time intervals when the observer-target range rate has
values between `min' and min+adjust.
If the search is for an absolute maximum `max', the
corresponding range is from max-adjust to `max'.
`adjust' is not used for searches for local extrema,
equality or inequality conditions.
step is the step size to be used in the search. `step' must
be short enough for a search using this step size
to locate the time intervals where the specified
range rate function is monotone increasing or
decreasing. However, `step' must not be *too* short, or
the search will take an unreasonable amount of time.
The choice of `step' affects the completeness but not
the precision of solutions found by this routine; the
precision is controlled by the convergence tolerance.
See the discussion of the parameter SPICE_GF_CNVTOL for
details.
`step' has units of TDB seconds.
nintvls is a parameter specifying the number of intervals that
can be accommodated by each of the dynamically allocated
windows used internally by this routine. `nintvls' should
be at least as large as the number of intervals within
the search region on which the specified range rate
function is monotone increasing or decreasing. See
the Examples section below for code examples illustrating
the use of this parameter.
cnfine is a SPICE window that confines the time period over
which the specified search is conducted. `cnfine' may
consist of a single interval or a collection of
intervals.
In some cases the confinement window can be used to
greatly reduce the time period that must be searched
for the desired solution. See the Particulars section
below for further discussion.
See the Examples section below for a code example
that shows how to create a confinement window.
-Detailed_Output
cnfine is the input confinement window, updated if necessary
so the control area of its data array indicates the
window's size and cardinality. The window data are
unchanged.
result is the window of intervals, contained within the
confinement window `cnfine', on which the specified
constraint is satisfied.
If `result' is non-empty on input, its contents will be
discarded before 'gfrr_c' conducts its search.
`result' must be declared with sufficient size to capture
the full set of time intervals within the search region
on which the specified constraint is satisfied.
If the search is for local extrema, or for absolute
extrema with `adjust' set to zero, then normally each
interval of `result' will be a singleton: the left and
right endpoints of each interval will be identical.
If no times within the confinement window satisfy the
constraint, `result' will be returned with a cardinality
of zero.
-Parameters
SPICE_GF_CNVTOL
is the convergence tolerance used for finding endpoints
of the intervals comprising the result window.
SPICE_GF_CNVTOL is used to determine when binary searches
for roots should terminate: when a root is bracketed
within an interval of length SPICE_GF_CNVTOL, the root is
considered to have been found.
The accuracy, as opposed to precision, of roots found
by this routine depends on the accuracy of the input
data. In most cases, the accuracy of solutions will be
inferior to their precision.
SPICE_GF_CNVTOL is declared in the header file SpiceGF.h.
-Exceptions
1) In order for this routine to produce correct results,
the step size must be appropriate for the problem at hand.
Step sizes that are too large may cause this routine to miss
roots; step sizes that are too small may cause this routine
to run unacceptably slowly and in some cases, find spurious
roots.
This routine does not diagnose invalid step sizes, except
that if the step size is non-positive, an error is signaled
by a routine in the call tree of this routine.
2) Due to numerical errors, in particular,
- Truncation error in time values
- Finite tolerance value
- Errors in computed geometric quantities
it is *normal* for the condition of interest to not always be
satisfied near the endpoints of the intervals comprising the
result window.
The result window may need to be contracted slightly by the
caller to achieve desired results. The SPICE window routine
wncond_c can be used to contract the result window.
3) If an error (typically cell overflow) occurs while performing
window arithmetic, the error will be diagnosed by a routine
in the call tree of this routine.
4) If the relational operator `relate' is not recognized, an
error is signaled by a routine in the call tree of this
routine.
5) If the aberration correction specifier contains an
unrecognized value, an error is signaled by a routine in the
call tree of this routine.
6) If 'adjust' is negative, the error SPICE(VALUEOUTOFRANGE) will
signal from a routine in the call tree of this routine.
A non-zero value for 'adjust' when 'relate' has any value other than
"ABSMIN" or "ABSMAX" causes the error SPICE(INVALIDVALUE) to
signal from a routine in the call tree of this routine.
7) If either of the input body names do not map to NAIF ID
codes, an error is signaled by a routine in the call tree of
this routine.
8) If required ephemerides or other kernel data are not
available, an error is signaled by a routine in the call tree
of this routine.
9) If the workspace interval count is less than 1, the error
SPICE(VALUEOUTOFRANGE) will be signaled.
10) If the required amount of workspace memory cannot be
allocated, the error SPICE(MALLOCFAILURE) will be
signaled.
11) If any input string argument pointer is null, the error
SPICE(NULLPOINTER) will be signaled.
12) If any input string argument is empty, the error
SPICE(EMPTYSTRING) will be signaled.
13) If either input cell has type other than SpiceDouble,
the error SPICE(TYPEMISMATCH) is signaled.
-Files
Appropriate kernels must be loaded by the calling program before
this routine is called.
The following data are required:
- SPK data: ephemeris data for target and observer for the
time period defined by the confinement window must be
loaded. If aberration corrections are used, the states of
target and observer relative to the solar system barycenter
must be calculable from the available ephemeris data.
Typically ephemeris data are made available by loading one
or more SPK files via furnsh_c.
In all cases, kernel data are normally loaded once per program
run, NOT every time this routine is called.
-Particulars
This routine determines if the caller-specified constraint condition
on the geometric event (range rate) is satisfied for any time intervals
within the confinement window 'cnfine'. If one or more such time
intervals exist, those intervals are added to the 'result' window.
This routine provides a simpler, but less flexible interface
than does the routine gfevnt_c for conducting the searches for
observer-target range rate value events. Applications that require
support for progress reporting, interrupt handling, non-default step
or refinement functions, or non-default convergence tolerance should
call gfevnt_c rather than this routine.
Below we discuss in greater detail aspects of this routine's
solution process that are relevant to correct and efficient
use of this routine in user applications.
The Search Process
==================
Regardless of the type of constraint selected by the caller, this
routine starts the search for solutions by determining the time
periods, within the confinement window, over which the specified
range rate function is monotone increasing and monotone decreasing.
Each of these time periods is represented by a SPICE window. Having
found these windows, all of the range rate function's local extrema
within the confinement window are known. Absolute extrema then can
be found very easily.
Within any interval of these "monotone" windows, there will be at
most one solution of any equality constraint. Since the boundary
of the solution set for any inequality constraint is contained in
the union of
- the set of points where an equality constraint is met
- the boundary points of the confinement window
the solutions of both equality and inequality constraints can be
found easily once the monotone windows have been found.
Step Size
=========
The monotone windows (described above) are found via a two-step
search process. Each interval of the confinement window is
searched as follows: first, the input step size is used to
determine the time separation at which the sign of the rate of
change of range rate will be sampled. Starting at
the left endpoint of an interval, samples will be taken at each
step. If a change of sign is found, a root has been bracketed; at
that point, the time at which the range rate is zero can be
found by a refinement process, for example, via binary search.
Note that the optimal choice of step size depends on the lengths
of the intervals over which the range rate function is monotone:
the step size should be shorter than the shortest of these
intervals (within the confinement window).
The optimal step size is *not* necessarily related to the lengths
of the intervals comprising the result window. For example, if
the shortest monotone interval has length 10 days, and if the
shortest result window interval has length 5 minutes, a step size
of 9.9 days is still adequate to find all of the intervals in the
result window. In situations like this, the technique of using
monotone windows yields a dramatic efficiency improvement over a
state-based search that simply tests at each step whether the
specified constraint is satisfied. The latter type of search can
miss solution intervals if the step size is longer than the
shortest solution interval.
Having some knowledge of the relative geometry of the target and
observer can be a valuable aid in picking a reasonable step size.
In general, the user can compensate for lack of such knowledge by
picking a very short step size; the cost is increased computation
time.
Note that the step size is not related to the precision with which
the endpoints of the intervals of the result window are computed.
That precision level is controlled by the convergence tolerance.
Convergence Tolerance
=====================
As described above, the root-finding process used by this routine
involves first bracketing roots and then using a search process to
locate them. "Roots" include times when extrema are attained and
times when the geometric quantity function is equal to a reference
value or adjusted extremum. All endpoints of the intervals comprising
the result window are either endpoints of intervals of the confinement
window or roots.
Once a root has been bracketed, a refinement process is used to
narrow down the time interval within which the root must lie.
This refinement process terminates when the location of the root
has been determined to within an error margin called the
"convergence tolerance." The convergence tolerance used by this
routine is set via the parameter SPICE_GF_CNVTOL.
The value of SPICE_GF_CNVTOL is set to a "tight" value so that the
tolerance doesn't limit the accuracy of solutions found by this
routine. In general the accuracy of input data will be the limiting
factor.
The user may change the convergence tolerance from the default
SPICE_GF_CNVTOL value by calling the routine gfstol_c, e.g.
gfstol_c( tolerance value in seconds )
Call gfstol_c prior to calling this routine. All subsequent
searches will use the updated tolerance value.
Searches over time windows of long duration may require use of
larger tolerance values than the default: the tolerance must be
large enough so that it, when added to or subtracted from the
confinement window's lower and upper bounds, yields distinct time
values.
Setting the tolerance tighter than SPICE_GF_CNVTOL is unlikely to be
useful, since the results are unlikely to be more accurate.
Making the tolerance looser will speed up searches somewhat,
since a few convergence steps will be omitted. However, in most
cases, the step size is likely to have a much greater effect
on processing time than would the convergence tolerance.
The Confinement Window
======================
The simplest use of the confinement window is to specify a time
interval within which a solution is sought. However, the
confinement window can, in some cases, be used to make searches
more efficient. Sometimes it's possible to do an efficient search
to reduce the size of the time period over which a relatively
slow search of interest must be performed.
Consider the following example: suppose one wishes to find the
times when the range rate between Io and the Earth attains a global
minimum over some (lengthy) time interval. There is one local
minimum every few days. The required step size for this search
must be smaller than the shortest interval on which the range rate
is monotone increasing or decreasing; this step size will be less
than half the average time between local minima. However, we know
that a global minimum can't occur when the Jupiter-Sun-Earth
angle is greater than 90 degrees. We can use a step size of a
half year to find the time period, within our original time
interval, during which this angle is less than 90 degrees; this
time period becomes the confinement window for our Earth-Io
range rate search. This way we've used a quick (due to the large
step size) search to cut out about half of the search period over
which we must perform a slower search using a small step size.
-Examples
The numerical results shown for these examples may differ across
platforms. The results depend on the SPICE kernels used as
input, the compiler and supporting libraries, and the machine
specific arithmetic implementation.
Use the meta-kernel shown below to load the required SPICE
kernels.
KPL/MK
File name: standard.tm
This meta-kernel is intended to support operation of SPICE
example programs. The kernels shown here should not be
assumed to contain adequate or correct versions of data
required by SPICE-based user applications.
In order for an application to use this meta-kernel, the
kernels referenced here must be present in the user's
current working directory.
The names and contents of the kernels referenced
by this meta-kernel are as follows:
File name Contents
--------- --------
de421.bsp Planetary ephemeris
pck00009.tpc Planet orientation and
radii
naif0009.tls Leapseconds
\begindata
KERNELS_TO_LOAD = ( 'de421.bsp',
'pck00009.tpc',
'naif0009.tls' )
\begintext
Example:
Determine the time windows from January 1, 2007 UTC to
April 1, 2007 UTC for which the sun-moon range rate satisfies the
relation conditions with respect to a reference value of
0.3365 km/s radians (this range rate known to occur within the
search interval). Also determine the time windows corresponding
to the local maximum and minimum range rate, and the absolute
maximum and minimum range rate during the search interval.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "SpiceUsr.h"
#define MAXWIN 20000
#define TIMFMT "YYYY-MON-DD HR:MN:SC.###"
#define TIMLEN 41
#define NLOOPS 7
int main( int argc, char **argv )
{
/.
Create the needed windows. Note, one window
consists of two values, so the total number
of cell values to allocate is twice
the number of intervals.
./
SPICEDOUBLE_CELL ( result, 2*MAXWIN );
SPICEDOUBLE_CELL ( cnfine, 2 );
SpiceDouble begtim;
SpiceDouble endtim;
SpiceDouble step;
SpiceDouble adjust;
SpiceDouble refval;
SpiceDouble beg;
SpiceDouble end;
SpiceChar begstr [ TIMLEN ];
SpiceChar endstr [ TIMLEN ];
SpiceChar * target = "MOON";
SpiceChar * abcorr = "NONE";
SpiceChar * obsrvr = "SUN";
SpiceInt count;
SpiceInt i;
SpiceInt j;
ConstSpiceChar * relate [NLOOPS] = { "=",
"<",
">",
"LOCMIN",
"ABSMIN",
"LOCMAX",
"ABSMAX",
};
/.
Load kernels.
./
furnsh_c( "standard.tm" );
/.
Store the time bounds of our search interval in
the cnfine confinement window.
./
str2et_c( "2007 JAN 01", &begtim );
str2et_c( "2007 APR 01", &endtim );
wninsd_c ( begtim, endtim, &cnfine );
/.
Search using a step size of 1 day (in units of seconds).
The reference value is .3365 km/s. We're not using the
adjustment feature, so we set 'adjust' to zero.
./
step = spd_c();
adjust = 0.;
refval = .3365;
for ( j = 0; j < NLOOPS; j++ )
{
printf ( "Relation condition: %s \n", relate[j] );
/.
Perform the search. The SPICE window 'result' contains
the set of times when the condition is met.
./
gfrr_c ( target,
abcorr,
obsrvr,
relate[j],
refval,
adjust,
step,
MAXWIN,
&cnfine,
&result );
count = wncard_c( &result );
/.
Display the results.
./
if (count == 0 )
{
printf ( "Result window is empty.\n\n" );
}
else
{
for ( i = 0; i < count; i++ )
{
/.
Fetch the endpoints of the Ith interval
of the result window.
./
wnfetd_c ( &result, i, &beg, &end );
timout_c ( beg, TIMFMT, TIMLEN, begstr );
timout_c ( end, TIMFMT, TIMLEN, endstr );
printf ( "Start time, drdt = %s \n", begstr );
printf ( "Stop time, drdt = %s \n", endstr );
}
}
printf("\n");
}
return( 0 );
}
The program outputs:
Relation condition: =
Start time, drdt = 2007-JAN-02 00:35:19.574
Stop time, drdt = 2007-JAN-02 00:35:19.574
Start time, drdt = 2007-JAN-19 22:04:54.899
Stop time, drdt = 2007-JAN-19 22:04:54.899
Start time, drdt = 2007-FEB-01 23:30:13.428
Stop time, drdt = 2007-FEB-01 23:30:13.428
Start time, drdt = 2007-FEB-17 11:10:46.540
Stop time, drdt = 2007-FEB-17 11:10:46.540
Start time, drdt = 2007-MAR-04 15:50:19.929
Stop time, drdt = 2007-MAR-04 15:50:19.929
Start time, drdt = 2007-MAR-18 09:59:05.959
Stop time, drdt = 2007-MAR-18 09:59:05.959
Relation condition: <
Start time, drdt = 2007-JAN-02 00:35:19.574
Stop time, drdt = 2007-JAN-19 22:04:54.899
Start time, drdt = 2007-FEB-01 23:30:13.428
Stop time, drdt = 2007-FEB-17 11:10:46.540
Start time, drdt = 2007-MAR-04 15:50:19.929
Stop time, drdt = 2007-MAR-18 09:59:05.959
Relation condition: >
Start time, drdt = 2007-JAN-01 00:00:00.000
Stop time, drdt = 2007-JAN-02 00:35:19.574
Start time, drdt = 2007-JAN-19 22:04:54.899
Stop time, drdt = 2007-FEB-01 23:30:13.428
Start time, drdt = 2007-FEB-17 11:10:46.540
Stop time, drdt = 2007-MAR-04 15:50:19.929
Start time, drdt = 2007-MAR-18 09:59:05.959
Stop time, drdt = 2007-APR-01 00:00:00.000
Relation condition: LOCMIN
Start time, drdt = 2007-JAN-11 07:03:58.988
Stop time, drdt = 2007-JAN-11 07:03:58.988
Start time, drdt = 2007-FEB-10 06:26:15.439
Stop time, drdt = 2007-FEB-10 06:26:15.439
Start time, drdt = 2007-MAR-12 03:28:36.404
Stop time, drdt = 2007-MAR-12 03:28:36.404
Relation condition: ABSMIN
Start time, drdt = 2007-JAN-11 07:03:58.988
Stop time, drdt = 2007-JAN-11 07:03:58.988
Relation condition: LOCMAX
Start time, drdt = 2007-JAN-26 02:27:33.766
Stop time, drdt = 2007-JAN-26 02:27:33.766
Start time, drdt = 2007-FEB-24 09:35:07.816
Stop time, drdt = 2007-FEB-24 09:35:07.816
Start time, drdt = 2007-MAR-25 17:26:56.150
Stop time, drdt = 2007-MAR-25 17:26:56.150
Relation condition: ABSMAX
Start time, drdt = 2007-MAR-25 17:26:56.150
Stop time, drdt = 2007-MAR-25 17:26:56.150
-Restrictions
1) The kernel files to be used by this routine must be loaded
(normally using the CSPICE routine furnsh_c) before this
routine is called.
2) This routine has the side effect of re-initializing the
range rate quantity utility package. Callers may themselves
need to re-initialize the range rate quantity utility
package after calling this routine.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
E.D. Wright (JPL)
-Version
-CSPICE Version 1.0.1, 28-FEB-2013 (NJB) (EDW)
Header was updated to discuss use of gfstol_c.
Edit to comments to correct search description.
Edits to Example section, proper description of "standard.tm"
meta kernel.
-CSPICE Version 1.0.0, 26-AUG-2009 (EDW) (NJB)
-Index_Entries
GF range rate search
-&
*/
{ /* Begin gfrr_c */
/*
Local variables
*/
doublereal * work;
static SpiceInt nw = SPICE_GF_NWRR;
SpiceInt nBytes;
/*
Participate in error tracing.
*/
chkin_c ( "gfrr_c" );
/*
Make sure cell data types are d.p.
*/
CELLTYPECHK2 ( CHK_STANDARD, "gfrr_c", SPICE_DP, cnfine, result );
/*
Initialize the input cells if necessary.
*/
CELLINIT2 ( cnfine, result );
/*
Check the input strings to make sure each pointer is non-null
and each string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "gfrr_c", target );
CHKFSTR ( CHK_STANDARD, "gfrr_c", abcorr );
CHKFSTR ( CHK_STANDARD, "gfrr_c", obsrvr );
CHKFSTR ( CHK_STANDARD, "gfrr_c", relate );
/*
Check the workspace size; some mallocs have a violent
dislike for negative allocation amounts. To be safe,
rule out a count of zero intervals as well.
*/
if ( nintvls < 1 )
{
setmsg_c ( "The specified workspace interval count # was "
"less than the minimum allowed value of one (1)." );
errint_c ( "#", nintvls );
sigerr_c ( "SPICE(VALUEOUTOFRANGE)" );
chkout_c ( "gfrr_c" );
return;
}
/*
Allocate the workspace. 'nintvls' indicates the maximum number of
intervals returned in 'result'. An interval consists of
two values.
*/
nintvls = 2 * nintvls;
nBytes = ( nintvls + SPICE_CELL_CTRLSZ ) * nw * sizeof(SpiceDouble);
work = (doublereal *) alloc_SpiceMemory( nBytes );
if ( !work )
{
setmsg_c ( "Workspace allocation of # bytes failed due to "
"malloc failure" );
errint_c ( "#", nBytes );
sigerr_c ( "SPICE(MALLOCFAILED)" );
chkout_c ( "gfrr_c" );
return;
}
/*
Let the f2'd routine do the work.
*/
gfrr_( ( char * ) target,
( char * ) abcorr,
( char * ) obsrvr,
( char * ) relate,
( doublereal * ) &refval,
( doublereal * ) &adjust,
( doublereal * ) &step,
( doublereal * ) (cnfine->base),
( integer * ) &nintvls,
( integer * ) &nw,
( doublereal * ) work,
( doublereal * ) (result->base),
( ftnlen ) strlen(target),
( ftnlen ) strlen(abcorr),
( ftnlen ) strlen(obsrvr),
( ftnlen ) strlen(relate) );
/*
De-allocate the workspace.
*/
free_SpiceMemory( work );
/*
Sync the output cell.
*/
if ( !failed_c() )
{
zzsynccl_c ( F2C, result ) ;
}
ALLOC_CHECK;
chkout_c ( "gfrr_c" );
} /* End gfrr_c */
void pcklof_c ( ConstSpiceChar * filename,
SpiceInt * handle )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
filename I Name of the file to be loaded.
handle O Loaded file's handle.
-Detailed_Input
filename Character name of the file to be loaded.
-Detailed_Output
handle Integer handle assigned to the file upon loading.
Other PCK routine will subsequently use this number
to refer to the file.
-Parameters
None.
-Exceptions
1) If an attempt is made to load more files than is specified
by the paramater ftsize defined in pckbsr_, the error
SPICE(PCKFILETABLEFULL) is signalled.
2) The error SPICE(EMPTYSTRING) is signalled if the input
string does not contain at least one character, since the
input string cannot be converted to a Fortran-style string
in this case.
3) The error SPICE(NULLPOINTER) is signalled if the input string
pointer is null.
This routine makes use of DAF file system routines and is subject
to all of the constraints imposed by the DAF fuile system. See
the DAF Required Reading or individual DAF routines for details.
-Files
A file specified by filename, to be loaded. The file is assigned a
handle by pcklof_c, which will be used by other routines to
refer to it.
-Particulars
If there is room for a new file in the file table, pcklof_c creates
an entry for it, and opens the file for reading.
Also, if the body table is empty, pcklof_c initializes it, this
being as good a place as any.
-Examples
Load a binary PCK kernel and return the integer handle.
pck = "/kernels/gen/pck/earth6.bpc";
pcklof_c ( pck, &handle );
Also see the Example in PCKLOF.FOR.
-Restrictions
None.
-Literature_References
DAF Required Reading
-Author_and_Institution
K.S. Zukor (JPL)
E.D. Wright (JPL)
-Version
-CSPICE Version 2.0.1, 20-MAR-1998 (EDW)
Minor correction to header.
-CSPICE Version 2.0.0, 08-FEB-1998 (NJB)
Input argument filename was changed to type ConstSpiceChar *.
Re-implemented routine without dynamically allocated, temporary
strings.
-CSPICE Version 1.0.0, 25-OCT-1997 (EDW)
-Index_Entries
load PCK orientation file
-&
*/
{ /* Begin pcklof_c */
/*
Participate in error tracing.
*/
chkin_c ( "pcklof_c" );
/*
Check the input string filename to make sure the pointer is non-null
and the string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "pcklof_c", filename );
/*
Call the f2c'd Fortran routine.
*/
pcklof_ ( ( char * ) filename,
( integer * ) handle,
( ftnlen ) strlen(filename) );
chkout_c ( "pcklof_c" );
} /* End pcklof_c */
void errch_c ( ConstSpiceChar * marker,
ConstSpiceChar * string )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- ---------------------------------------------------
marker I A substring of the error message to be replaced.
string I The character string to substitute for marker.
-Detailed_Input
marker is a character string that marks a position in
the long error message where a character string
is to be substituted. Leading and trailing blanks
in marker are not significant.
Case IS significant: "XX" is considered to be
a different marker from "xx".
string is a character string that will be substituted for
the first occurrence of marker in the long error
message. This occurrence of the substring indicated
by marker will be removed and replaced by string.
Leading and trailing blanks in string are not
significant. However, if string is completely blank,
a single blank character will be substituted for
the marker.
-Detailed_Output
None.
-Parameters
LMSGLN is the maximum length of the long error message. See
the include file errhnd.inc for the value of LMSGLN.
-Exceptions
1) If the character string resulting from the substitution
exceeds the maximum length of the long error message, the
long error message is truncated on the right. No error is
signaled.
2) If marker is blank, no substitution is performed. No error
is signaled.
3) If string is blank, then the first occurrence of marker is
replaced by a single blank.
4) If marker does not appear in the long error message, no
substitution is performed. No error is signaled.
5) If changes to the long error message are disabled, this
routine has no effect.
6) The error SPICE(EMPTYSTRING) is signaled if either input string
does not contain at least one character, since an input string
cannot be converted to a Fortran-style string in this case.
7) The error SPICE(NULLPOINTER) is signalled if either string pointer
argument is null.
-Files
None.
-Particulars
The purpose of this routine is to allow you to tailor the long
error message to include specific information that is available
only at run time. This capability is somewhat like being able to
put variables in your error messages.
-Examples
1) In this example, the marker is "#". We'll signal a file
open error, and we'll include in the error message the name
of the file we tried to open. There are three steps:
-- Set the long message, using a marker for the location
where a value is to be substituted.
-- Substitute the file name into the error message.
-- Signal the error (causing output of error messages)
using the CSPICE routine sigerr_c.
/.
Error on file open attempt. Signal an error.
The character string variable FILE contains the
file name.
After the call to errch_c, the long error message
will contain the file name held in the string
FILE. For example, if FILE contains the name
"MYFILE.DAT", the long error message will be
"File open error. File is MYFILE.DAT."
./
setmsg_c ( "File open error. File is #." );
errch_c ( "#", FILE );
sigerr_c ( "SPICE(FILEOPENFAILED)" );
2) Same example as (1), except this time we'll use a better-
looking and more descriptive marker than "#". Instead,
we'll use the marker "FILENAME". This does not affect the
long error message; it just makes the code more readable.
/.
Error on file open attempt. Signal an error.
The character string variable FILE contains the
file name.
./
setmsg_c ( "File open error. File is FILENAME.");
errch_c ( "FILENAME", FILE );
sigerr_c ( "SPICE(FILEOPENFAILED)" );
3) Same example as (2), except this time there's a problem with
the variable FILE: it's blank. This time, the code fragment
/.
Error on file open attempt. Signal an error.
The character string variable FILE contains the
file name.
./
setmsg_c ( "File open error. File is FILENAME." );
errch_c ( "FILENAME", FILE );
sets the long error message to
"File open error. File is "
-Restrictions
1) The caller must ensure that the message length, after sub-
stitution is performed, doesn't exceed LMSGLN characters.
See errch.c.
-Literature_References
None.
-Author_and_Institution
J.E. McLean (JPL)
N.J. Bachman (JPL)
-Version
-CSPICE Version 1.2.0, 08-FEB-1998 (NJB)
Re-implemented routine without dynamically allocated, temporary
strings. Made various header fixes.
-CSPICE Version 1.0.0, 25-OCT-1997 (EDW)
-Index_Entries
insert string into error message text
-&
*/
{ /* Begin errch_c */
/*
Check the input strings to make sure the pointers are non-null
and the string lengths are non-zero. Since we don't check in
prior to this, use the discovery check-in option.
*/
CHKFSTR ( CHK_DISCOVER, "errch_c", marker );
CHKFSTR ( CHK_DISCOVER, "errch_c", string );
/*
Call the f2c'd Fortran routine.
*/
errch_ ( ( char * ) marker,
( char * ) string,
( ftnlen ) strlen(marker),
( ftnlen ) strlen(string) );
} /* End errch_c */
void pcpool_c ( ConstSpiceChar * name,
SpiceInt n,
SpiceInt lenvals,
const void * cvals )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
name I The kernel pool name to associate with cvals.
n I The number of values to insert.
lenvals I The lengths of the strings in the array cvals.
cvals I An array of strings to insert into the kernel pool.
-Detailed_Input
name is the name of the kernel pool variable to associate
with the values supplied in the array cvals. 'name' is
restricted to a length of 32 characters or less.
n is the number of values to insert into the kernel pool.
lenvals is the length of the strings in the array cvals,
including the null terminators.
cvals is an array of strings to insert into the kernel
pool. cvals should be declared as follows:
char cvals[n][lenvals];
-Detailed_Output
None.
-Parameters
None.
-Exceptions
1) If name is already present in the kernel pool and there
is sufficient room to hold all values supplied in values,
the old values associated with name will be overwritten.
2) If there is not sufficient room to insert a new variable
into the kernel pool and name is not already present in
the kernel pool, the error SPICE(KERNELPOOLFULL) is
signaled by a routine in the call tree to this routine.
3) If there is not sufficient room to insert the values associated
with name, the error SPICE(NOMOREROOM) will be signaled.
4) If either input string pointer is null, the error
SPICE(NULLPOINTER) will be signaled.
5) If the input string name has length zero, the error
SPICE(EMPTYSTRING) will be signaled.
6) If the input cvals string length is less than 2, the error
SPICE(STRINGTOOSHORT) will be signaled.
7) The error 'SPICE(BADVARNAME)' signals if the kernel pool
variable name length exceeds 32.
-Files
None.
-Particulars
This entry point provides a programmatic interface for inserting
character data into the SPICE kernel pool without reading an
external file.
-Examples
The following example program shows how a topocentric frame for a
point on the surface of the earth may be defined at run time using
pcpool_c, pdpool_c, and pipool_c. In this example, the surface
point is associated with the body code 300000. To facilitate
testing, the location of the surface point coincides with that of
the DSN station DSS-12; the reference frame MYTOPO defined here
coincides with the reference frame DSS-12_TOPO.
#include <stdio.h>
#include "SpiceUsr.h"
int main()
{
/.
The first angle is the negative of the longitude of the
surface point; the second angle is the negative of the
point's colatitude.
./
SpiceDouble angles [3] = { -243.1945102442646,
-54.7000629043147,
180.0 };
SpiceDouble et = 0.0;
SpiceDouble rmat [3][3];
SpiceInt axes [3] = { 3, 2, 3 };
SpiceInt center = 300000;
SpiceInt frclass = 4;
SpiceInt frclsid = 1500000;
SpiceInt frcode = 1500000;
/.
Define the MYTOPO reference frame.
Note that the third argument in the pcpool_c calls is
the length of the final string argument, including the
terminating null character.
./
pipool_c ( "FRAME_MYTOPO", 1, &frcode );
pcpool_c ( "FRAME_1500000_NAME", 1, 7, "MYTOPO" );
pipool_c ( "FRAME_1500000_CLASS", 1, &frclass );
pipool_c ( "FRAME_1500000_CLASS_ID", 1, &frclsid );
pipool_c ( "FRAME_1500000_CENTER", 1, ¢er );
pcpool_c ( "OBJECT_300000_FRAME", 1, 7, "MYTOPO" );
pcpool_c ( "TKFRAME_MYTOPO_RELATIVE", 1, 7, "ITRF93" );
pcpool_c ( "TKFRAME_MYTOPO_SPEC", 1, 7, "ANGLES" );
pcpool_c ( "TKFRAME_MYTOPO_UNITS", 1, 8, "DEGREES" );
pipool_c ( "TKFRAME_MYTOPO_AXES", 3, axes );
pdpool_c ( "TKFRAME_MYTOPO_ANGLES", 3, angles );
/.
Load a high precision binary earth PCK. Also load a
topocentric frame kernel for DSN stations. The file names
shown here are simply examples; users should replace these
with the names of appropriate kernels.
./
furnsh_c ( "earth_000101_060207_051116.bpc" );
furnsh_c ( "earth_topo_050714.tf" );
/.
Look up transformation from DSS-12_TOPO frame to MYTOPO frame.
This transformation should differ by round-off error from
the identity matrix.
./
pxform_c ( "DSS-12_TOPO", "MYTOPO", et, rmat );
printf ( "\n"
"DSS-12_TOPO to MYTOPO transformation at "
"et %23.16e = \n"
"\n"
" %25.16f %25.16f %25.16f\n"
" %25.16f %25.16f %25.16f\n"
" %25.16f %25.16f %25.16f\n",
et,
rmat[0][0], rmat[0][1], rmat[0][2],
rmat[1][0], rmat[1][1], rmat[1][2],
rmat[2][0], rmat[2][1], rmat[2][2] );
return ( 0 );
}
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
W.L. Taber (JPL)
-Version
-CSPICE Version 1.3.3, 17-JAN-2014 (NJB)
Updated Index_Entries section.
-CSPICE Version 1.3.2, 10-FEB-2010 (EDW)
Added mention of the restriction on kernel pool variable
names to 32 characters or less.
Reordered header sections to conform to SPICE convention.
-CSPICE Version 1.3.1, 17-NOV-2005 (NJB)
Replaced code fragment in Examples section of header with
smaller, complete program.
-CSPICE Version 1.3.0, 12-JUL-2002 (NJB)
Call to C2F_CreateStrArr_Sig replaced with call to C2F_MapStrArr.
-CSPICE Version 1.2.0, 28-AUG-2001 (NJB)
Const-qualified input array cvals.
-CSPICE Version 1.1.0, 14-FEB-2000 (NJB)
Calls to C2F_CreateStrArr replaced with calls to error-signaling
version of this routine: C2F_CreateStrArr_Sig.
-CSPICE Version 1.0.0, 18-JUN-1999 (NJB) (WLT)
-Index_Entries
Set the value of a character_variable in the kernel_pool
-&
*/
{ /* Begin pcpool_c */
/*
Local variables
*/
SpiceChar * fCvalsArr;
SpiceInt fCvalsLen;
/*
Participate in error tracing.
*/
chkin_c ( "pcpool_c" );
/*
Check the input kernel variable name to make sure the pointer is
non-null and the string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "pcpool_c", name );
/*
Make sure the input string pointer for the cvals array is non-null
and that the length lenvals is sufficient.
*/
CHKOSTR ( CHK_STANDARD, "pcpool_c", cvals, lenvals );
/*
Create a Fortran-style string array.
*/
C2F_MapStrArr ( "pcpool_c",
n, lenvals, cvals, &fCvalsLen, &fCvalsArr );
if ( failed_c() )
{
chkout_c ( "pcpool_c" );
return;
}
/*
Call the f2c'd routine.
*/
pcpool_ ( ( char * ) name,
( integer * ) &n,
( char * ) fCvalsArr,
( ftnlen ) strlen(name),
( ftnlen ) fCvalsLen );
/*
Free the dynamically allocated array.
*/
free ( fCvalsArr );
chkout_c ( "pcpool_c" );
} /* End pcpool_c */
void cklpf_c ( ConstSpiceChar * filename,
SpiceInt * handle )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
filename I Name of the CK file to be loaded.
handle O Loaded file's handle.
-Detailed_Input
filename is the name of a C-kernel file to be loaded.
-Detailed_Output
handle is an integer handle assigned to the file upon loading.
Almost every other CK routine will subsequently use
this number to refer to the file.
-Parameters
ftsize is the maximum number of pointing files that can
be loaded by CKLPF at any given time for use by the
readers.
-Exceptions
1) If an attempt is made to load more files than is specified
by the parameter ftsize, the error "SPICE(CKTOOMANYFILES)"
is signalled.
2) If an attempt is made to open more DAF files than is specified
by the parameter ftsize in DAFAH, an error is signalled by a
routine that this routine calls.
3) If the file specified by filename can not be opened, an error
is signalled by a routine that this routine calls.
4) If the file specified by filename has already been loaded,
it will become the "last-loaded" file. (The readers
search the last-loaded file first.)
-Files
The C-kernel file specified by filename is loaded. The file is
assigned an integer handle by CKLPF. Other CK routines will refer
to this file by its handle.
-Particulars
See Particulars in ckbsr.
If there is room for a new file, CKLPF opens the file for
reading. This routine must be called prior to a call to CKGP or
CKGPAV.
CK readers search files loaded with CKLPF in the reverse order
in which they were loaded. That is, last-loaded files are
searched first.
-Examples
ck_kern = "/kernels/mpf/ck/lander_nominal.bck";
cklpf_c ( ck_kern, &hand );
Also see the Example in ckbsr.for.
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
J.M. Lynch (JPL)
J.E. McLean (JPL)
M.J. Spencer (JPL)
R.E. Thurman (JPL)
I.M. Underwood (JPL)
E.D. Wright (JPL)
B.V. Semenov (JPL)
-Version
-CSPICE Version 2.0.1, 31-JAN-2008 (BVS)
Removed '-Revisions' from the header.
-CSPICE Version 2.0.0, 08-FEB-1998 (NJB)
Input argument filename changed to type ConstSpiceChar *;
name was changed to "filename" from "fname."
References to C2F_CreateStr_Sig were removed; code was
cleaned up accordingly. String checks are now done using
the macro CHKFSTR.
-CSPICE Version 1.0.0, 25-OCT-1997 (EDW)
-Index_Entries
load ck pointing file
-&
*/
{ /* Begin spklef_c */
/*
Participate in error tracing.
*/
chkin_c ( "cklpf_c" );
/*
Check the input string filename to make sure the pointer is non-null
and the string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "cklpf_c", filename );
/*
Call the f2c'd Fortran routine.
*/
cklpf_ ( ( char * ) filename,
( integer * ) handle,
( ftnlen ) strlen(filename) );
chkout_c ( "cklpf_c" );
} /* end cklpf_c */
void swpool_c ( ConstSpiceChar * agent,
SpiceInt nnames,
SpiceInt lenvals,
const void * names )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
agent I The name of an agent to be notified after updates.
nnames I The number of variables to associate with agent.
lenvals I Length of strings in the names array.
names I Variable names whose update causes the notice.
-Detailed_Input
agent is the name of a routine or entry point (agency) that
will want to know when a some variables in the kernel
pool have been updated.
nnames is the number of kernel pool variable names that will
be associated with agent.
lenvals is the length of the strings in the array names,
including the null terminators.
names is an array of names of variables in the kernel pool.
Whenever any of these is updated, a notice will be
posted for agent so that one can quickly check
whether needed data has been modified.
-Detailed_Output
None.
-Parameters
None.
-Files
None.
-Exceptions
1) If sufficient room is not available to hold a name or new agent,
a routine in the call tree for this routine will signal an error.
2) If either of the input string pointers are null, the error
SPICE(NULLPOINTER) will be signaled.
3) If any input string agent has length zero, the error
SPICE(EMPTYSTRING) will be signaled.
4) The caller must pass a value indicating the length of the strings
in the names array. If this value is not at least 2, the error
SPICE(STRINGTOOSHORT) will be signaled.
-Particulars
The kernel pool is a convenient place to store a wide variety of
data needed by routines in CSPICE and routines that interface with
CSPICE routines. However, when a single name has a large quantity
of data associated with it, it becomes inefficient to constantly
query the kernel pool for values that are not updated on a frequent
basis.
This entry point allows a routine to instruct the kernel pool to
post a message whenever a particular value gets updated. In this
way, a routine can quickly determine whether or not data it requires
has been updated since the last time the data was accessed. This
makes it reasonable to buffer the data in local storage and update
it only when a variable in the kernel pool that affects this data
has been updated.
Note that swpool_c has a side effect. Whenever a call to swpool_c
is made, the agent specified in the calling sequence is added to the
list of agents that should be notified that an update of its
variables has occurred. In other words the code
swpool_c ( agent, nnames, lenvals, names );
cvpool_c ( agent, &update );
will always return update as SPICETRUE.
This feature allows for a slightly cleaner use of swpool_c and
cvpool_c as shown in the example below. Because swpool_c
automatically loads agent into the list of agents to notify of a
kernel pool update, you do not have to include the code for fetching
the initial values of the kernel variables in the initialization
portion of a subroutine. Instead, the code for the first fetch from
the pool is the same as the code for fetching when the pool is
updated.
-Examples
Suppose that you have an application subroutine, MYTASK, that
needs to access a large data set in the kernel pool. If this
data could be kept in local storage and kernel pool queries
performed only when the data in the kernel pool has been
updated, the routine can perform much more efficiently.
The code fragment below illustrates how you might make use of this
feature.
#include "SpiceUsr.h"
.
.
.
/.
On the first call to this routine establish those variables
that we will want to read from the kernel pool only when
new values have been assigned.
./
if ( first )
{
first = SPICEFALSE;
swpool_c ( "MYTASK", nnames, lenvals, names );
}
/.
If any of the variables has been updated, fetch them from the
kernel pool.
./
cvpool_c ( "MYTASK", &update );
if ( update )
{
for ( i = 0; i < NVAR; i++ )
{
gdpool_c( MYTASK_VAR[i], 1, NMAX, n[i], val[i], &found[i] );
}
}
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
W.L. Taber (JPL)
-Version
-CSPICE Version 1.3.0, 27-AUG-2002 (NJB)
Call to C2F_CreateStrArr_Sig replaced with call to C2F_MapStrArr.
-CSPICE Version 1.2.0, 28-AUG-2001 (NJB)
Const-qualified input array names.
-CSPICE Version 1.1.0, 14-FEB-2000 (NJB)
Calls to C2F_CreateStrArr replaced with calls to error-signaling
version of this routine: C2F_CreateStrArr_Sig.
-CSPICE Version 1.0.0, 05-JUN-1999 (NJB) (WLT)
-Index_Entries
Watch for an update to a kernel pool variable
Notify a routine of an update to a kernel pool variable
-&
*/
{ /* Begin swpool_c */
/*
Local variables
*/
SpiceChar * fCvalsArr;
SpiceInt fCvalsLen;
/*
Participate in error tracing.
*/
chkin_c ( "swpool_c" );
/*
Make sure the input string pointer for agent is non-null
and that the length is sufficient.
*/
CHKFSTR ( CHK_STANDARD, "swpool_c", agent );
/*
Make sure the input string pointer for the names array is non-null
and that the length lenvals is sufficient.
*/
CHKOSTR ( CHK_STANDARD, "swpool_c", names, lenvals );
/*
Create a Fortran-style string array.
*/
C2F_MapStrArr ( "swpool_c",
nnames, lenvals, names, &fCvalsLen, &fCvalsArr );
if ( failed_c() )
{
chkout_c ( "swpool_c" );
return;
}
/*
Call the f2c'd routine.
*/
swpool_ ( ( char * ) agent,
( integer * ) &nnames,
( char * ) fCvalsArr,
( ftnlen ) strlen(agent),
( ftnlen ) fCvalsLen );
/*
Free the dynamically allocated array.
*/
free ( fCvalsArr );
chkout_c ( "swpool_c" );
} /* End swpool_c */
void ckw01_c ( SpiceInt handle,
SpiceDouble begtim,
SpiceDouble endtim,
SpiceInt inst,
ConstSpiceChar * ref,
SpiceBoolean avflag,
ConstSpiceChar * segid,
SpiceInt nrec,
ConstSpiceDouble sclkdp [],
ConstSpiceDouble quats [][4],
ConstSpiceDouble avvs [][3] )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
handle I Handle of an open CK file.
begtim I The beginning encoded SCLK of the segment.
endtim I The ending encoded SCLK of the segment.
inst I The NAIF instrument ID code.
ref I The reference frame of the segment.
avflag I True if the segment will contain angular velocity.
segid I Segment identifier.
nrec I Number of pointing records.
sclkdp I Encoded SCLK times.
quats I Quaternions representing instrument pointing.
avvs I Angular velocity vectors.
-Detailed_Input
handle is the handle of the CK file to which the segment will
be written. The file must have been opened with write
access.
begtim is the beginning encoded SCLK time of the segment. This
value should be less than or equal to the first time in
the segment.
endtim is the encoded SCLK time at which the segment ends.
This value should be greater than or equal to the last
time in the segment.
inst is the NAIF integer ID code for the instrument.
ref is a character string which specifies the
reference frame of the segment. This should be one of
the frames supported by the SPICELIB routine NAMFRM
which is an entry point of FRAMEX.
avflag is a logical flag which indicates whether or not the
segment will contain angular velocity.
segid is the segment identifier. A CK segment identifier may
contain up to 40 characters, excluding the terminating
null.
nrec is the number of pointing instances in the segment.
sclkdp are the encoded spacecraft clock times associated with
each pointing instance. These times must be strictly
increasing.
quats is an array of SPICE-style quaternions representing a
sequence of C-matrices. See the discussion of "Quaternion
Styles" in the Particulars section below.
avvs are the angular velocity vectors (optional).
If avflag is FALSE then this array is ignored by the
routine, however it still must be supplied as part of
the calling sequence.
-Detailed_Output
None. See Files section.
-Parameters
None.
-Exceptions
1) If handle is not the handle of a C-kernel opened for writing
the error will be diagnosed by routines called by this
routine.
2) If segid is more than 40 characters long, the error
SPICE(SEGIDTOOLONG) is signaled.
3) If segid contains any nonprintable characters, the error
SPICE(NONPRINTABLECHARS) is signaled.
4) If the first encoded SCLK time is negative then the error
SPICE(INVALIDSCLKTIME) is signaled. If any subsequent times
are negative the error SPICE(TIMESOUTOFORDER) is signaled.
5) If the encoded SCLK times are not strictly increasing,
the error SPICE(TIMESOUTOFORDER) is signaled.
6) If begtim is greater than sclkdp[0] or endtim is less than
sclkdp[nrec-1], the error SPICE(INVALIDDESCRTIME) is
signaled.
7) If the name of the reference frame is not one of those
supported by the SPICELIB routine NAMFRM, the error
SPICE(INVALIDREFFRAME) is signaled.
8) If nrec, the number of pointing records, is less than or
equal to 0, the error SPICE(INVALIDNUMRECS) is signaled.
9) If any quaternion has magnitude zero, the error
SPICE(ZEROQUATERNION) is signaled.
-Files
This routine adds a type 1 segment to a C-kernel. The C-kernel
may be either a new one or an existing one opened for writing.
-Particulars
For a detailed description of a type 1 CK segment please see the
CK Required Reading.
This routine relieves the user from performing the repetitive
calls to the DAF routines necessary to construct a CK segment.
Quaternion Styles
-----------------
There are different "styles" of quaternions used in
science and engineering applications. Quaternion styles
are characterized by
- The order of quaternion elements
- The quaternion multiplication formula
- The convention for associating quaternions
with rotation matrices
Two of the commonly used styles are
- "SPICE"
> Invented by Sir William Rowan Hamilton
> Frequently used in mathematics and physics textbooks
- "Engineering"
> Widely used in aerospace engineering applications
CSPICE function interfaces ALWAYS use SPICE quaternions.
Quaternions of any other style must be converted to SPICE
quaternions before they are passed to CSPICE functions.
Relationship between SPICE and Engineering Quaternions
------------------------------------------------------
Let M be a rotation matrix such that for any vector V,
M*V
is the result of rotating V by theta radians in the
counterclockwise direction about unit rotation axis vector A.
Then the SPICE quaternions representing M are
(+/-) ( cos(theta/2),
sin(theta/2) A(1),
sin(theta/2) A(2),
sin(theta/2) A(3) )
while the engineering quaternions representing M are
(+/-) ( -sin(theta/2) A(1),
-sin(theta/2) A(2),
-sin(theta/2) A(3),
cos(theta/2) )
For both styles of quaternions, if a quaternion q represents
a rotation matrix M, then -q represents M as well.
Given an engineering quaternion
QENG = ( q0, q1, q2, q3 )
the equivalent SPICE quaternion is
QSPICE = ( q3, -q0, -q1, -q2 )
Associating SPICE Quaternions with Rotation Matrices
----------------------------------------------------
Let FROM and TO be two right-handed reference frames, for
example, an inertial frame and a spacecraft-fixed frame. Let the
symbols
V , V
FROM TO
denote, respectively, an arbitrary vector expressed relative to
the FROM and TO frames. Let M denote the transformation matrix
that transforms vectors from frame FROM to frame TO; then
V = M * V
TO FROM
where the expression on the right hand side represents left
multiplication of the vector by the matrix.
Then if the unit-length SPICE quaternion q represents M, where
q = (q0, q1, q2, q3)
the elements of M are derived from the elements of q as follows:
+- -+
| 2 2 |
| 1 - 2*( q2 + q3 ) 2*(q1*q2 - q0*q3) 2*(q1*q3 + q0*q2) |
| |
| |
| 2 2 |
M = | 2*(q1*q2 + q0*q3) 1 - 2*( q1 + q3 ) 2*(q2*q3 - q0*q1) |
| |
| |
| 2 2 |
| 2*(q1*q3 - q0*q2) 2*(q2*q3 + q0*q1) 1 - 2*( q1 + q2 ) |
| |
+- -+
Note that substituting the elements of -q for those of q in the
right hand side leaves each element of M unchanged; this shows
that if a quaternion q represents a matrix M, then so does the
quaternion -q.
To map the rotation matrix M to a unit quaternion, we start by
decomposing the rotation matrix as a sum of symmetric
and skew-symmetric parts:
2
M = [ I + (1-cos(theta)) OMEGA ] + [ sin(theta) OMEGA ]
symmetric skew-symmetric
OMEGA is a skew-symmetric matrix of the form
+- -+
| 0 -n3 n2 |
| |
OMEGA = | n3 0 -n1 |
| |
| -n2 n1 0 |
+- -+
The vector N of matrix entries (n1, n2, n3) is the rotation axis
of M and theta is M's rotation angle. Note that N and theta
are not unique.
Let
C = cos(theta/2)
S = sin(theta/2)
Then the unit quaternions Q corresponding to M are
Q = +/- ( C, S*n1, S*n2, S*n3 )
The mappings between quaternions and the corresponding rotations
are carried out by the CSPICE routines
q2m_c {quaternion to matrix}
m2q_c {matrix to quaternion}
m2q_c always returns a quaternion with scalar part greater than
or equal to zero.
SPICE Quaternion Multiplication Formula
---------------------------------------
Given a SPICE quaternion
Q = ( q0, q1, q2, q3 )
corresponding to rotation axis A and angle theta as above, we can
represent Q using "scalar + vector" notation as follows:
s = q0 = cos(theta/2)
v = ( q1, q2, q3 ) = sin(theta/2) * A
Q = s + v
Let Q1 and Q2 be SPICE quaternions with respective scalar
and vector parts s1, s2 and v1, v2:
Q1 = s1 + v1
Q2 = s2 + v2
We represent the dot product of v1 and v2 by
<v1, v2>
and the cross product of v1 and v2 by
v1 x v2
Then the SPICE quaternion product is
Q1*Q2 = s1*s2 - <v1,v2> + s1*v2 + s2*v1 + (v1 x v2)
If Q1 and Q2 represent the rotation matrices M1 and M2
respectively, then the quaternion product
Q1*Q2
represents the matrix product
M1*M2
-Examples
This example writes a type 1 C-kernel segment for the
Galileo scan platform to a previously opened file attached to
handle.
/.
Include CSPICE interface definitions.
./
#include "SpiceUsr.h"
.
.
.
/.
Assume arrays of quaternions, angular velocities, and the
associated SCLK times are produced elsewhere.
./
.
.
.
/.
The subroutine ckw01_c needs the following items for the
segment descriptor:
1) SCLK limits of the segment.
2) Instrument code.
3) Reference frame.
4) The angular velocity flag.
./
begtim = (SpiceChar *) sclk[0];
endtim = (SpiceChar *) sclk[nrec-1];
inst = -77001;
ref = "J2000";
avflag = SPICETRUE;
segid = "GLL SCAN PLT - DATA TYPE 1";
/.
Write the segment.
./
ckw01_c ( handle, begtim, endtim, inst, ref, avflag,
segid, nrec, sclkdp, quats, avvs );
.
.
.
/.
After all segments are written, close the C-kernel.
./
ckcls_c ( handle );
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
K.R. Gehringer (JPL)
N.J. Bachman (JPL)
J.M. Lynch (JPL)
-Version
-CSPICE Version 2.0.0, 01-JUN-2010 (NJB)
The check for non-unit quaternions has been replaced
with a check for zero-length quaternions. (The
implementation of the check is located in ckw01_.)
-CSPICE Version 1.3.2, 27-FEB-2008 (NJB)
Updated header; added information about SPICE
quaternion conventions.
-CSPICE Version 1.3.1, 12-JUN-2006 (NJB)
Corrected typo in example, the sclk indexes for the begtim
and endtim assignments used FORTRAN convention.
-CSPICE Version 1.3.0, 28-AUG-2001 (NJB)
Changed prototype: inputs sclkdp, quats, and avvs are now
const-qualified. Implemented interface macros for casting
these inputs to const.
-CSPICE Version 1.2.0, 02-SEP-1999 (NJB)
Local type logical variable now used for angular velocity
flag used in interface of ckw01_.
-CSPICE Version 1.1.0, 08-FEB-1998 (NJB)
References to C2F_CreateStr_Sig were removed; code was
cleaned up accordingly. String checks are now done using
the macro CHKFSTR.
-CSPICE Version 1.0.0, 25-OCT-1997 (NJB)
Based on SPICELIB Version 2.0.0, 28-DEC-1993 (WLT)
-Index_Entries
write ck type_1 pointing data segment
-&
*/
{ /* Begin ckw01_c */
/*
Local variables
*/
logical avf;
/*
Participate in error handling.
*/
chkin_c ( "ckw01_c" );
/*
Check the input strings to make sure the pointers
are non-null and the string lengths are non-zero.
*/
CHKFSTR ( CHK_STANDARD, "ckw01_c", ref );
CHKFSTR ( CHK_STANDARD, "ckw01_c", segid );
/*
Get a type logical copy of the a.v. flag.
*/
avf = avflag;
/*
Write the segment. Note that the quaternion and angular velocity
arrays DO NOT require transposition!
*/
ckw01_( ( integer * ) &handle,
( doublereal * ) &begtim,
( doublereal * ) &endtim,
( integer * ) &inst,
( char * ) ref,
( logical * ) &avf,
( char * ) segid,
( integer * ) &nrec,
( doublereal * ) sclkdp,
( doublereal * ) quats,
( doublereal * ) avvs,
( ftnlen ) strlen(ref),
( ftnlen ) strlen(segid) );
chkout_c ( "ckw01_c" );
} /* End ckw01_c */
void pgrrec_c ( ConstSpiceChar * body,
SpiceDouble lon,
SpiceDouble lat,
SpiceDouble alt,
SpiceDouble re,
SpiceDouble f,
SpiceDouble rectan[3] )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
body I Body with which coordinate system is associated.
lon I Planetographic longitude of a point (radians).
lat I Planetographic latitude of a point (radians).
alt I Altitude of a point above reference spheroid.
re I Equatorial radius of the reference spheroid.
f I Flattening coefficient.
rectan O Rectangular coordinates of the point.
-Detailed_Input
body Name of the body with which the planetographic
coordinate system is associated.
`body' is used by this routine to look up from the
kernel pool the prime meridian rate coefficient giving
the body's spin sense. See the Files and Particulars
header sections below for details.
lon Planetographic longitude of the input point. This is
the angle between the prime meridian and the meridian
containing the input point. For bodies having
prograde (aka direct) rotation, the direction of
increasing longitude is positive west: from the +X
axis of the rectangular coordinate system toward the
-Y axis. For bodies having retrograde rotation, the
direction of increasing longitude is positive east:
from the +X axis toward the +Y axis.
The earth, moon, and sun are exceptions:
planetographic longitude is measured positive east for
these bodies.
The default interpretation of longitude by this
and the other planetographic coordinate conversion
routines can be overridden; see the discussion in
Particulars below for details.
Longitude is measured in radians. On input, the range
of longitude is unrestricted.
lat Planetographic latitude of the input point. For a
point P on the reference spheroid, this is the angle
between the XY plane and the outward normal vector at
P. For a point P not on the reference spheroid, the
planetographic latitude is that of the closest point
to P on the spheroid.
Latitude is measured in radians. On input, the
range of latitude is unrestricted.
alt Altitude of point above the reference spheroid.
Units of `alt' must match those of `re'.
re Equatorial radius of a reference spheroid. This
spheroid is a volume of revolution: its horizontal
cross sections are circular. The shape of the
spheroid is defined by an equatorial radius `re' and
a polar radius `rp'. Units of `re' must match those of
`alt'.
f Flattening coefficient =
(re-rp) / re
where `rp' is the polar radius of the spheroid, and the
units of `rp' match those of `re'.
-Detailed_Output
rectan The rectangular coordinates of the input point. See
the discussion below in the Particulars header section
for details.
The units associated with `rectan' are those associated
with the inputs `alt' and `re'.
-Parameters
None.
-Exceptions
1) If the body name `body' cannot be mapped to a NAIF ID code,
and if `body' is not a string representation of an integer,
the error SPICE(IDCODENOTFOUND) will be signaled.
2) If the kernel variable
BODY<ID code>_PGR_POSITIVE_LON
is present in the kernel pool but has a value other
than one of
'EAST'
'WEST'
the error SPICE(INVALIDOPTION) will be signaled. Case
and blanks are ignored when these values are interpreted.
3) If polynomial coefficients for the prime meridian of `body'
are not available in the kernel pool, and if the kernel
variable BODY<ID code>_PGR_POSITIVE_LON is not present in
the kernel pool, the error SPICE(MISSINGDATA) will be signaled.
4) If the equatorial radius is non-positive, the error
SPICE(VALUEOUTOFRANGE) is signaled.
5) If the flattening coefficient is greater than or equal to one,
the error SPICE(VALUEOUTOFRANGE) is signaled.
6) The error SPICE(EMPTYSTRING) is signaled if the input
string `body' does not contain at least one character, since the
input string cannot be converted to a Fortran-style string in
this case.
7) The error SPICE(NULLPOINTER) is signaled if the input string
pointer `body' is null.
-Files
This routine expects a kernel variable giving body's prime
meridian angle as a function of time to be available in the
kernel pool. Normally this item is provided by loading a PCK
file. The required kernel variable is named
BODY<body ID>_PM
where <body ID> represents a string containing the NAIF integer
ID code for `body'. For example, if `body' is "JUPITER", then
the name of the kernel variable containing the prime meridian
angle coefficients is
BODY599_PM
See the PCK Required Reading for details concerning the prime
meridian kernel variable.
The optional kernel variable
BODY<body ID>_PGR_POSITIVE_LON
also is normally defined via loading a text kernel. When this
variable is present in the kernel pool, the prime meridian
coefficients for `body' are not required by this routine. See the
Particulars section below for details.
-Particulars
Given the planetographic coordinates of a point, this routine
returns the body-fixed rectangular coordinates of the point. The
body-fixed rectangular frame is that having the X-axis pass
through the 0 degree latitude 0 degree longitude direction, the
Z-axis pass through the 90 degree latitude direction, and the
Y-axis equal to the cross product of the unit Z-axis and X-axis
vectors.
The planetographic definition of latitude is identical to the
planetodetic (also called "geodetic" in SPICE documentation)
definition. In the planetographic coordinate system, latitude is
defined using a reference spheroid. The spheroid is
characterized by an equatorial radius and a polar radius. For a
point P on the spheroid, latitude is defined as the angle between
the X-Y plane and the outward surface normal at P. For a point P
off the spheroid, latitude is defined as the latitude of the
nearest point to P on the spheroid. Note if P is an interior
point, for example, if P is at the center of the spheroid, there
may not be a unique nearest point to P.
In the planetographic coordinate system, longitude is defined
using the spin sense of the body. Longitude is positive to the
west if the spin is prograde and positive to the east if the spin
is retrograde. The spin sense is given by the sign of the first
degree term of the time-dependent polynomial for the body's prime
meridian Euler angle "W": the spin is retrograde if this term is
negative and prograde otherwise. For the sun, planets, most
natural satellites, and selected asteroids, the polynomial
expression for W may be found in a SPICE PCK kernel.
The earth, moon, and sun are exceptions: planetographic longitude
is measured positive east for these bodies.
If you wish to override the default sense of positive longitude
for a particular body, you can do so by defining the kernel
variable
BODY<body ID>_PGR_POSITIVE_LON
where <body ID> represents the NAIF ID code of the body. This
variable may be assigned either of the values
'WEST'
'EAST'
For example, you can have this routine treat the longitude
of the earth as increasing to the west using the kernel
variable assignment
BODY399_PGR_POSITIVE_LON = 'WEST'
Normally such assignments are made by placing them in a text
kernel and loading that kernel via furnsh_c.
The definition of this kernel variable controls the behavior of
the CSPICE planetographic routines
pgrrec_c
recpgr_c
dpgrdr_c
drdpgr_c
It does not affect the other CSPICE coordinate conversion
routines.
-Examples
Numerical results shown for this example may differ between
platforms as the results depend on the SPICE kernels used as
input and the machine specific arithmetic implementation.
1) Find the rectangular coordinates of the point having Mars
planetographic coordinates:
longitude = 90 degrees west
latitude = 45 degrees north
altitude = 300 km
#include <stdio.h>
#include "SpiceUsr.h"
int main()
{
/.
Local variables
./
SpiceDouble alt;
SpiceDouble f;
SpiceDouble lat;
SpiceDouble lon;
SpiceDouble radii [3];
SpiceDouble re;
SpiceDouble rectan [3];
SpiceDouble rp;
SpiceInt n;
/.
Load a PCK file containing a triaxial
ellipsoidal shape model and orientation
data for Mars.
./
furnsh_c ( "pck00008.tpc" );
/.
Look up the radii for Mars. Although we
omit it here, we could first call badkpv_c
to make sure the variable BODY499_RADII
has three elements and numeric data type.
If the variable is not present in the kernel
pool, bodvrd_c will signal an error.
./
bodvrd_c ( "MARS", "RADII", 3, &n, radii );
/.
Compute flattening coefficient.
./
re = radii[0];
rp = radii[2];
f = ( re - rp ) / re;
/.
Do the conversion. Note that we must provide
longitude and latitude in radians.
./
lon = 90.0 * rpd_c();
lat = 45.0 * rpd_c();
alt = 3.e2;
pgrrec_c ( "mars", lon, lat, alt, re, f, rectan );
printf ( "\n"
"Planetographic coordinates:\n"
"\n"
" Longitude (deg) = %18.9e\n"
" Latitude (deg) = %18.9e\n"
" Altitude (km) = %18.9e\n"
"\n"
"Ellipsoid shape parameters:\n"
"\n"
" Equatorial radius (km) = %18.9e\n"
" Polar radius (km) = %18.9e\n"
" Flattening coefficient = %18.9e\n"
"\n"
"Rectangular coordinates:\n"
"\n"
" X (km) = %18.9e\n"
" Y (km) = %18.9e\n"
" Z (km) = %18.9e\n"
"\n",
lon / rpd_c(),
lat / rpd_c(),
alt,
re,
rp,
f,
rectan[0],
rectan[1],
rectan[2] );
return ( 0 );
}
Output from this program should be similar to the following
(rounding and formatting differ across platforms):
Planetographic coordinates:
Longitude (deg) = 9.000000000e+01
Latitude (deg) = 4.500000000e+01
Altitude (km) = 3.000000000e+02
Ellipsoid shape parameters:
Equatorial radius (km) = 3.396190000e+03
Polar radius (km) = 3.376200000e+03
Flattening coefficient = 5.886007556e-03
Rectangular coordinates:
X (km) = 1.604650025e-13
Y (km) = -2.620678915e+03
Z (km) = 2.592408909e+03
2) Below is a table showing a variety of rectangular coordinates
and the corresponding Mars planetographic coordinates. The
values are computed using the reference spheroid having radii
Equatorial radius: 3397
Polar radius: 3375
Note: the values shown above may not be current or suitable
for your application.
Corresponding rectangular and planetographic coordinates are
listed to three decimal places.
rectan[0] rectan[1] rectan[2] lon lat alt
------------------------------------------------------------------
3397.000 0.000 0.000 0.000 0.000 0.000
-3397.000 0.000 0.000 180.000 0.000 0.000
-3407.000 0.000 0.000 180.000 0.000 10.000
-3387.000 0.000 0.000 180.000 0.000 -10.000
0.000 -3397.000 0.000 90.000 0.000 0.000
0.000 3397.000 0.000 270.000 0.000 0.000
0.000 0.000 3375.000 0.000 90.000 0.000
0.000 0.000 -3375.000 0.000 -90.000 0.000
0.000 0.000 0.000 0.000 90.000 -3375.000
3) Below we show the analogous relationships for the earth,
using the reference ellipsoid radii
Equatorial radius: 6378.140
Polar radius: 6356.750
Note the change in longitudes for points on the +/- Y axis
for the earth vs the Mars values.
rectan[0] rectan[1] rectan[2] lon lat alt
------------------------------------------------------------------
6378.140 0.000 0.000 0.000 0.000 0.000
-6378.140 0.000 0.000 180.000 0.000 0.000
-6388.140 0.000 0.000 180.000 0.000 10.000
-6368.140 0.000 0.000 180.000 0.000 -10.000
0.000 -6378.140 0.000 270.000 0.000 0.000
0.000 6378.140 0.000 90.000 0.000 0.000
0.000 0.000 6356.750 0.000 90.000 0.000
0.000 0.000 -6356.750 0.000 -90.000 0.000
0.000 0.000 0.000 0.000 90.000 -6356.750
-Restrictions
None.
-Author_and_Institution
C.H. Acton (JPL)
N.J. Bachman (JPL)
H.A. Neilan (JPL)
B.V. Semenov (JPL)
W.L. Taber (JPL)
-Literature_References
None.
-Version
-CSPICE Version 1.0.0, 26-DEC-2004 (CHA) (NJB) (HAN) (BVS) (WLT)
-Index_Entries
convert planetographic to rectangular coordinates
-&
*/
{ /* Begin pgrrec_c */
/*
Participate in error tracing.
*/
if ( return_c() )
{
return;
}
chkin_c ( "pgrrec_c" );
/*
Check the input string body to make sure the pointer is non-null
and the string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "pgrrec_c", body );
/*
Call the f2c'd Fortran routine.
*/
pgrrec_ ( ( char * ) body,
( doublereal * ) &lon,
( doublereal * ) &lat,
( doublereal * ) &alt,
( doublereal * ) &re,
( doublereal * ) &f,
( doublereal * ) rectan,
( ftnlen ) strlen(body) );
chkout_c ( "pgrrec_c" );
} /* End pgrrec_c */
