void psv2pl_c ( ConstSpiceDouble point[3],
ConstSpiceDouble span1[3],
ConstSpiceDouble span2[3],
SpicePlane * plane )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
point,
span1,
span2 I A point and two spanning vectors defining a plane.
plane O A CSPICE plane representing the plane.
-Detailed_Input
point,
span1,
span2 are, respectively, a point and two spanning vectors
that define a geometric plane in three-dimensional
space. The plane is the set of vectors
point + s * span1 + t * span2
where s and t are real numbers. The spanning
vectors span1 and span2 must be linearly
independent, but they need not be orthogonal or
unitized.
-Detailed_Output
plane is a CSPICE plane that represents the geometric
plane defined by point, span1, and span2.
-Parameters
None.
-Exceptions
1) If span1 and span2 are linearly dependent, then the vectors
point, span1, and span2 do not define a plane. The error
SPICE(DEGENERATECASE) is signaled.
-Files
None.
-Particulars
CSPICE geometry routines that deal with planes use the `plane'
data type to represent input and output planes. This data type
makes the subroutine interfaces simpler and more uniform.
The CSPICE routines that produce CSPICE planes from data that
define a plane are:
nvc2pl_c ( Normal vector and constant to plane )
nvp2pl_c ( Normal vector and point to plane )
psv2pl_c ( Point and spanning vectors to plane )
The CSPICE routines that convert CSPICE planes to data that
define a plane are:
pl2nvc_c ( Plane to normal vector and constant )
pl2nvp_c ( Plane to normal vector and point )
pl2psv_c ( Plane to point and spanning vectors )
Any of these last three routines may be used to convert this
routine's output, plane, to another representation of a
geometric plane.
-Examples
1) Project a vector v orthogonally onto a plane defined by
point, span1, and span2. proj is the projection we want; it
is the closest vector in the plane to v.
psv2pl_c ( point, span1, span2, &plane );
vprjp_c ( v, &plane, proj );
2) Find the plane determined by a spacecraft's position vector
relative to a central body and the spacecraft's velocity
vector. We assume that all vectors are given in the same
coordinate system.
/.
pos is the spacecraft's position, relative to
the central body. vel is the spacecraft's velocity
vector. pos is a point (vector, if you like) in
the orbit plane, and it is also one of the spanning
vectors of the plane.
./
psv2pl_c ( pos, pos, vel, &plane );
-Restrictions
None.
-Literature_References
[1] `Calculus and Analytic Geometry', Thomas and Finney.
-Author_and_Institution
N.J. Bachman (JPL)
-Version
-CSPICE Version 1.0.0, 05-MAR-1999 (NJB)
-Index_Entries
point and spanning vectors to plane
-&
*/
{ /* Begin psv2pl_c */
/*
This routine checks in only if an error is discovered.
*/
if ( return_c () )
{
return;
}
/*
Find the unitized cross product of SPAN1 and SPAN2; this is our
unit normal vector, or possibly its inverse.
*/
ucrss_c ( span1, span2, plane->normal );
if ( vzero_c ( plane->normal ) )
{
chkin_c ( "psv2pl_c" );
setmsg_c ( "Spanning vectors are parallel." );
sigerr_c ( "SPICE(DEGENERATECASE)" );
chkout_c ( "psv2pl_c" );
return;
}
/*
Find the plane constant corresponding to the unit normal
vector we've found.
*/
plane->constant = vdot_c ( plane->normal, point );
/*
The constant should be the distance of the plane from the
origin. If the constant is negative, negate both it and the
normal vector.
*/
if ( plane->constant < 0. )
{
plane->constant = - (plane->constant);
vminus_c ( plane->normal, plane->normal );
}
} /* End psv2pl_c */
void reordl_c ( ConstSpiceInt * iorder,
SpiceInt ndim,
SpiceBoolean * array )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
iorder I Order vector to be used to re-order array.
ndim I Dimension of array.
array I/O Array to be re-ordered.
-Detailed_Input
iorder is the order vector to be used to re-order the input
array. The first element of iorder is the index of
the first item of the re-ordered array, and so on.
Note that the order imposed by reordl_c is not the
same order that would be imposed by a sorting
routine. In general, the order vector will have
been created (by one of the order routines) for
a related array, as illustrated in the example below.
The elements of iorder range from zero to ndim-1.
ndim is the number of elements in the input array.
array on input, is an array containing some number of
elements in unspecified order.
-Detailed_Output
array on output, is the same array, with the elements
in re-ordered as specified by iorder.
-Parameters
None.
-Exceptions
1) If memory cannot be allocated to create a Fortran-style version of
the input order vector, the error SPICE(MALLOCFAILED) is signaled.
2) If memory cannot be allocated to create a type "logical" copy of the
the input SpiceBoolean array, the error SPICE(MALLOCFAILED) is
signaled.
3) If ndim < 2, this routine executes a no-op. This case is
not an error.
-Files
None.
-Particulars
reordl_c uses a cyclical algorithm to re-order the elements of
the array in place. After re-ordering, element iorder[0] of
the input array is the first element of the output array,
element iorder[1] is the input array is the second element of
the output array, and so on.
The order vector used by reordl_c is typically created for
a related array by one of the order*_c routines, as shown in
the example below.
-Examples
In the following example, the order*_c and reord*_c routines are
used to sort four related arrays (containing the names,
masses, integer ID codes, and visual magnitudes for a group
of satellites). This is representative of the typical use of
these routines.
#include "SpiceUsr.h"
.
.
.
/.
Sort the object arrays by name.
./
orderc_c ( namlen, names, n, iorder );
ordvec
reordc_c ( iorder, n, namlen, names );
reordd_c ( iorder, n, masses );
reordi_c ( iorder, n, codes );
reordd_c ( iorder, n, vmags );
-Restrictions
None.
-Author_and_Institution
N.J. Bachman (JPL)
W.L. Taber (JPL)
I.M. Underwood (JPL)
-Literature_References
None.
-Version
-CSPICE Version 1.0.0, 10-JUL-2002 (NJB) (WLT) (IMU)
-Index_Entries
reorder a logical array
-&
*/
{ /* Begin reordl_c */
/*
Local variables
*/
logical * lArray;
SpiceInt aSize;
SpiceInt i ;
SpiceInt * ordvec;
SpiceInt vSize;
/*
If the input array doesn't have at least two elements, return
immediately.
*/
if ( ndim < 2 )
{
return;
}
/*
Get a local copy of the input order vector; map the vector's contents
to the range 1:ndim.
*/
vSize = ndim * sizeof(SpiceInt);
ordvec = (SpiceInt *) malloc( vSize );
if ( ordvec == 0 )
{
chkin_c ( "reordl_c" );
setmsg_c ( "Failure on malloc call to create array "
"for Fortran-style order vector. Tried "
"to allocate # bytes." );
errint_c ( "#", vSize );
sigerr_c ( "SPICE(MALLOCFAILED)" );
chkout_c ( "reordl_c" );
return;
}
for ( i = 0; i < ndim; i++ )
{
ordvec[i] = iorder[i] + 1;
}
/*
Get a local copy of the input logical array; use type logical
to ensure compatibility with code translated by f2c.
*/
aSize = ndim * sizeof(logical);
lArray = (logical *) malloc( aSize );
if ( lArray == 0 )
{
free ( ordvec );
chkin_c ( "reordl_c" );
setmsg_c ( "Failure on malloc call to create array "
"for Fortran-style order vector. Tried "
"to allocate # bytes." );
errint_c ( "#", aSize );
sigerr_c ( "SPICE(MALLOCFAILED)" );
chkout_c ( "reordl_c" );
return;
}
for ( i = 0; i < ndim; i++ )
{
lArray[i] = array[i];
}
reordl_ ( ( integer * ) ordvec,
( integer * ) &ndim,
( logical * ) lArray );
/*
Write the re-ordered result to the output array.
*/
for ( i = 0; i < ndim; i++ )
{
array[i] = (SpiceBoolean) lArray[i];
}
free ( ordvec );
free ( lArray );
} /* End reordl_c */
void insrtc_c ( ConstSpiceChar * item,
SpiceCell * set )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
item I Item to be inserted.
set I/O Insertion set.
-Detailed_Input
item is an item which is to be inserted into the specified
set. item may or may not already be an element of the
set. Trailing blanks in item are not significant.
set is a CSPICE set. set must be declared as a character
SpiceCell.
On input, set may or may not contain the input item
as an element.
-Detailed_Output
set on output contains the union of the input set and
the singleton set containing the input item.
-Parameters
None.
-Exceptions
1) If the input set argument is a SpiceCell of type other than
character, the error SPICE(TYPEMISMATCH) is signaled.
2) If the insertion of the element into the set causes an excess
of elements, the error SPICE(SETEXCESS) is signaled.
3) If the input set argument does not qualify as a CSPICE set,
the error SPICE(NOTASET) will be signaled. CSPICE sets have
their data elements sorted in increasing order and contain
no duplicate data elements.
4) If the input string pointer is null, the error SPICE(NULLPOINTER)
is signaled.
-Files
None.
-Particulars
None.
-Examples
1) In the following example, the element "PLUTO" is removed from
the character set planets and inserted into the character set
asteroids.
#include "SpiceUsr.h"
.
.
.
/.
Declare the sets with string length NAMLEN and with maximum
number of elements MAXSIZ.
./
SPICECHAR_CELL ( planets, MAXSIZ, NAMLEN );
SPICECHAR_CELL ( asteroids, MAXSIZ, NAMLEN );
.
.
.
removc_c ( "PLUTO", &planets );
insrtc_c ( "PLUTO", &asteroids );
If "PLUTO" is not an element of planets, then the contents of
planets are not changed. Similarly, if "PLUTO" is already an
element of asteroids, the contents of asteroids remain unchanged.
Because inserting an element into a set can increase the
cardinality of the set, an error may occur in the insertion
routines.
-Restrictions
1) String comparisons performed by this routine are Fortran-style:
trailing blanks in the input set or key value are ignored.
This gives consistent behavior with CSPICE code generated by
the f2c translator, as well as with the Fortran SPICE Toolkit.
Note that this behavior is not identical to that of the ANSI
C library functions strcmp and strncmp.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
C.A. Curzon (JPL)
W.L. Taber (JPL)
I.M. Underwood (JPL)
-Version
-CSPICE Version 2.1.0, 07-MAR-2009 (NJB)
This file now includes the header file f2cMang.h.
This header supports name mangling of f2c library
functions.
-CSPICE Version 2.0.0, 01-NOV-2005 (NJB)
Bug fix: when the item to be inserted would, after
truncation to the set's string length, match an item
already in the set, no insertion is performed. Previously
the truncated string was inserted, corrupting the set.
Long error message was updated to include size of
set into which insertion was attempted.
-CSPICE Version 1.0.0, 21-AUG-2002 (NJB) (CAC) (WLT) (IMU)
-Index_Entries
insert an item into a character set
-&
*/
{
/*
f2c library utility prototypes
*/
extern integer s_cmp (char *a, char *b, ftnlen la, ftnlen lb );
/*
Local macros
*/
#define ARRAY( i ) ( (SpiceChar *)(set->data) + (i)*(set->length) )
/*
local variables
*/
SpiceBoolean inSet;
SpiceChar * cdata;
SpiceInt i;
SpiceInt loc;
SpiceInt slen;
/*
Use discovery check-in.
Check the input string pointer to make sure it's not null.
*/
CHKPTR ( CHK_DISCOVER, "insrtc_c", item );
/*
Make sure we're working with a character cell.
*/
CELLTYPECHK ( CHK_DISCOVER, "insrtc_c", SPICE_CHR, set );
/*
Make sure the input cell is a set.
*/
CELLISSETCHK ( CHK_DISCOVER, "insrtc_c", set );
/*
Initialize the set if it's not already initialized.
*/
CELLINIT ( set );
/*
Let slen be the effective string length of the input item.
Characters beyond the string length of the set are ignored.
*/
slen = mini_c ( 2, set->length, strlen(item) );
/*
Is the item already in the set? If not, it needs to be inserted.
*/
cdata = (SpiceChar *) (set->data);
/*
The following call will give the location of the last element
less than or equal to the item to be inserted. If the item
differs from an element of the set only in characters that would
be truncated, no insertion will occur. Even in this case, the
insertion point `loc' returned by lstlec_c will be correct.
*/
loc = lstlec_c ( item, set->card, set->length, cdata );
inSet = ( loc > -1 )
&& ( s_cmp( (SpiceChar *)item, ARRAY(loc),
slen, strlen(ARRAY(loc)) ) == 0 );
if ( inSet )
{
return;
}
/*
It's an error if the set has no room left.
*/
if ( set->card == set->size )
{
chkin_c ( "insrtc_c" );
setmsg_c ( "An element could not be inserted into the set "
"due to lack of space; set size is #." );
errint_c ( "#", set->size );
sigerr_c ( "SPICE(SETEXCESS)" );
chkout_c ( "insrtc_c" );
return;
}
/*
Make room by moving the items that come after index loc in the set.
Insert the item after index loc.
*/
for ( i = (set->card); i > (loc+1); i-- )
{
SPICE_CELL_SET_C( ARRAY(i-1), i, set );
}
/*
This insertion macro will truncate the item to be inserted, if
necessary. The input item will be null-terminated.
*/
SPICE_CELL_SET_C( item, loc+1, set );
/*
Increment the set's cardinality.
*/
(set->card) ++;
}
void ekaclc_c ( SpiceInt handle,
SpiceInt segno,
ConstSpiceChar * column,
SpiceInt vallen,
const void * cvals,
ConstSpiceInt * entszs,
ConstSpiceBoolean * nlflgs,
ConstSpiceInt * rcptrs,
SpiceInt * wkindx )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
handle I EK file handle.
segno I Number of segment to add column to.
column I Column name.
vallen I Length of character values.
cvals I Character values to add to column.
entszs I Array of sizes of column entries.
nlflgs I Array of null flags for column entries.
rcptrs I Record pointers for segment.
wkindx I-O Work space for column index.
-Detailed_Input
handle the handle of an EK file that is open for writing.
A "begin segment for fast write" operation must
have already been performed for the designated
segment.
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.
column is the name of the column to be added. All of
the data for the named column will be added in
one shot.
vallen is the length of the strings in the cvals array.
The array should be declared with dimensions
[nrows][vallen]
where nrows is the number of rows in the column.
cvals is an array containing the entire set of column
entries for the specified column. The entries
are listed in row-order: the column entry for the
first row of the segment is first, followed by the
column entry for the second row, and so on. The
number of column entries must match the declared
number of rows in the segment. For columns having
fixed-size entries, a null entry must be allocated
the same amount of space occupied by a non-null
entry in the array cvals. For columns having
variable-size entries, null entries do not require
any space in the cvals* array, but in any case must
have their allocated space described correctly by
the corresponding element of the entszs array
(described below).
entszs is an array containing sizes of column entries.
The Ith element of entszs gives the size of the
Ith column entry. entszs is used only for columns
having variable-size entries. For such columns,
the dimension of entszs must be at least nrows.
The size of null entries should be set to zero.
For columns having fixed-size entries, the
dimension of this array may be any positive value.
nlflgs is an array of logical flags indicating whether
the corresponding entries are null. If the Ith
element of nlflgs is SPICEFALSE, the Ith column entry
defined by cvals and entszs is added to the
current segment in the specified kernel file.
If the Ith element of nlfgls is SPICETRUE, the
contents of the Ith column entry are undefined.
nlflgs is used only for columns that allow null
values; it's ignored for other columns.
rcptrs is an array of record pointers for the input
segment. This array is obtained as an output
from ekifld_c, the routine called to initiate a
fast write.
wkindx is a work space array used for building a column
index. If the column is indexed, the dimension of
wkindx_c must be at nrows, where nrows is the number
of rows in the column. If the column is not
indexed, this work space is not used, so the
dimension may be any positive value.
-Detailed_Output
None. See $Particulars for a description of the effect of this
routine.
-Parameters
None.
-Exceptions
1) If handle is invalid, the error will be diagnosed by routines
called by this routine.
2) If column is not the name of a declared column, the error
SPICE(NOCOLUMN) will be signaled.
3) If column specifies a column of whose data type is not
character, the error SPICE(WRONGDATATYPE) will be
signalled.
4) If the specified column already contains ANY entries, the
error will be diagnosed by routines called by this routine.
5) If an I/O error occurs while reading or writing the indicated
file, the error will be diagnosed by routines called by this
routine.
6) If the string pointer for column is null, the error
SPICE(NULLPOINTER) will be signaled.
7) If the input string column has length zero, the error
SPICE(EMPTYSTRING) will be signaled.
8) If the string pointer for cvals is null, the error
SPICE(NULLPOINTER) will be signaled.
9) If the string length vallen 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 modifies the named
EK file by adding data to the specified column. This routine
writes the entire contents of the specified column in one shot.
This routine creates columns much more efficiently than can be
done by sequential calls to ekacec_c, but has the drawback that
the caller must use more memory for the routine's inputs. This
routine cannot be used to add data to a partially completed
column.
-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 create the
first of the segments described above.
#include "SpiceUsr.h"
#include <stdio.h>
void main()
{
/.
Constants
./
#define CNMLEN ( CSPICE_EK_COL_NAM_LEN + 1 )
#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 NROWS 9
#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 rcptrs [ NROWS ];
SpiceInt segno;
SpiceInt sizes [ NROWS ];
SpiceInt wkindx [ 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. We presume the number of rows
of data is known in advance.
./
ekifld_c ( handle, TABLE, NCOLS, NROWS, CNMLEN,
cnames, DECLEN, cdecls, &segno, rcptrs );
/.
At this point, arrays containing data for the
segment's columns may be filled in. The names
of the data arrays are shown below.
Column Data array
"ORDER_ID" ordids
"CUSTOMER_ID" cstids
"LAST_NAME" lnames
"FIRST_NAME" fnames
"ORDER_DATE" odates
"COST" costs
The null flags array indicates which entries are null.
It is ignored for columns that don't allow null
values. In this case, only the COST column allows
nulls.
Fill in data arrays and null flag arrays here. This code
section would normally be replaced by calls to user functions
returning column values.
./
for ( i = 0; i < NROWS; i++ )
{
ordids[i] = i;
cstids[i] = i*100;
costs [i] = (SpiceDouble) 100*i;
sprintf ( fnames[i], "Order %d Customer first name", i );
sprintf ( lnames[i], "Order %d Customer last name", i );
sprintf ( dateStr, "1998 Mar %d", i );
utc2et_c ( dateStr, ets+i );
nlflgs[i] = SPICEFALSE;
}
nlflgs[1] = SPICETRUE;
/.
The sizes array shown below is ignored for scalar
and fixed-size array columns, so we need not
initialize it. For variable-size arrays, the
Ith element of the sizes array must contain the size
of the Ith column entry in the column being written.
Normally, the sizes array would be reset for each
variable-size column.
Add the columns of data to the segment. All of the
data for each column is written in one shot.
./
ekacli_c ( handle, segno, "order_id", ordids,
sizes, nlflgs, rcptrs, wkindx );
ekacli_c ( handle, segno, "customer_id", cstids,
sizes, nlflgs, rcptrs, wkindx );
ekaclc_c ( handle, segno, "last_name", LNMLEN,
lnames, sizes, nlflgs, rcptrs, wkindx );
ekaclc_c ( handle, segno, "first_name", FNMLEN,
fnames, sizes, nlflgs, rcptrs, wkindx );
ekacld_c ( handle, segno, "order_date", ets,
sizes, nlflgs, rcptrs, wkindx );
ekacld_c ( handle, segno, "cost", costs,
sizes, nlflgs, rcptrs, wkindx );
/.
Complete the segment. The rcptrs array is that
returned by ekifld_c.
./
ekffld_c ( handle, segno, rcptrs );
/.
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
1) Only one segment can be created at a time using the fast
write routines.
2) No other EK operation may interrupt a fast write. For
example, it is not valid to issue a query while a fast write
is in progress.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
-Version
-CSPICE Version 1.2.2, 14-AUG-2006 (EDW)
Replace mention of ldpool_c with furnsh_c.
-CSPICE Version 1.2.1, 09-JAN-2002 (NJB)
Documentation change: instances of the phrase "fast load"
were replaced with "fast write."
Const-qualified input array cvals.
-CSPICE Version 1.1.0, 12-JUL-1998 (NJB)
Bug fix: now counts elements rather than rows for vector-valued
columns.
Bug fix: now uses dynamically allocated array of type logical
to interface with underlying f2c'd function ekaclc_.
Now maps segno from C to Fortran range.
Added "undef" of masking macro. Changed input pointer types
to pointers to const objects.
Replaced eksdsc_ call with ekssum_c call. This removes unsightly
references to segment descriptor alignments.
Fixed some chkout_c calls which referenced ekifld_c.
-CSPICE Version 1.0.0, 25-FEB-1999 (NJB)
Based on SPICELIB Version 1.0.0, 08-NOV-1995 (NJB)
-Index_Entries
write entire character column to EK segment
-&
*/
{ /* Begin ekaclc_c */
/*
Local variables
*/
SpiceBoolean fnd;
logical * logicalFlags;
SpiceEKSegSum summary;
SpiceChar ** cvalsPtr;
SpiceChar * fCvalsArr;
SpiceInt i;
SpiceInt fCvalsLen;
SpiceInt fSegno;
SpiceInt ncols;
SpiceInt nelts;
SpiceInt nrows;
SpiceInt size;
/*
Participate in error tracing.
*/
chkin_c ( "ekaclc_c" );
/*
Check the column name to make sure the pointer is non-null
and the string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "ekaclc_c", column );
/*
Check the value 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, "ekaclc_c", cvals, vallen );
/*
Get the row count for this segment.
*/
ekssum_c ( handle, segno, &summary );
nrows = summary.nrows;
/*
Locate the index of this column in the segment descriptor.
*/
ncols = summary.ncols;
i = 0;
fnd = SPICEFALSE;
while ( ( i < ncols ) && ( !fnd ) )
{
if ( eqstr_c( column, summary.cnames[i] ) )
{
fnd = SPICETRUE;
}
else
{
i++;
}
}
if ( !fnd )
{
setmsg_c ( "Column <#> does not belong to segment #. " );
errch_c ( "#", column );
errint_c ( "#", segno );
sigerr_c ( "SPICE(NOCOLUMN)" );
chkout_c ( "ekaclc_c" );
return;
}
/*
Now i is the index within the segment descriptor of the column
descriptor for the column of interest. Get the dimension information
for this column.
*/
size = summary.cdescrs[i].size;
/*
Compute the total string count of the input array. If the column
has fixed-size entries, we ignore the entszs array. Otherwise, the
entszs array tells us how many strings we're getting.
*/
if ( size == SPICE_EK_VARSIZ )
{
nelts = sumai_c ( entszs, nrows );
}
else
{
nelts = nrows * size;
}
/*
Allocate an array of logicals and assign values from the input
array of SpiceBooleans.
*/
logicalFlags = ( logical * ) malloc ( nelts * sizeof(logical) );
if ( !logicalFlags )
{
setmsg_c ( "Failure on malloc call to create null flag array "
"for column values." );
sigerr_c ( "SPICE(MALLOCFAILED)" );
chkout_c ( "ekaclc_c" );
return;
}
/*
Copy the input null flags to our array of type logical.
*/
for ( i = 0; i < nrows; i++ )
{
logicalFlags[i] = nlflgs[i];
}
/*
We need to make a blank-padded version of the cvals array.
We'll first allocate an array of character pointers to index
the values, initialize this array, and use it to produce
a dynamically allocated array of Fortran-style strings.
*/
cvalsPtr = ( SpiceChar ** ) malloc ( nelts * sizeof(SpiceChar *) );
if ( cvalsPtr == 0 )
{
free ( logicalFlags );
setmsg_c ( "Failure on malloc call to create pointer array "
"for column values." );
sigerr_c ( "SPICE(MALLOCFAILED)" );
chkout_c ( "ekaclc_c" );
return;
}
for ( i = 0; i < nelts; i++ )
{
cvalsPtr[i] = (SpiceChar *)cvals + ( i * vallen );
}
C2F_CreateFixStrArr ( nelts,
vallen,
( ConstSpiceChar ** ) cvalsPtr,
&fCvalsLen,
&fCvalsArr );
if ( failed_c() )
{
free ( logicalFlags );
free ( cvalsPtr );
chkout_c ( "ekaclc_c" );
return;
}
/*
Map the segment number to the Fortran range.
*/
fSegno = segno + 1;
ekaclc_ ( ( integer * ) &handle,
( integer * ) &fSegno,
( char * ) column,
( char * ) fCvalsArr,
( integer * ) entszs,
( logical * ) logicalFlags,
( integer * ) rcptrs,
( integer * ) wkindx,
( ftnlen ) strlen(column),
( ftnlen ) fCvalsLen );
/*
Clean up all of our dynamically allocated arrays.
*/
free ( cvalsPtr );
free ( fCvalsArr );
free ( logicalFlags );
chkout_c ( "ekaclc_c" );
} /* End ekaclc_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 */
GetData::GetData(string dskfilepath, string currentPath){
SpiceInt handle;
SpiceDLADescr dladsc;
//int i,j,k,l,norme1,norme2,p,q;
//int flag = 0;
//int cont;
FILE *f;
printf("getdata\n");
string fname = "/Desktop/commonF_aft.dat";
fname = currentPath + fname;
dasopr_c(dskfilepath.c_str(), &handle);
dlabfs_c(handle,&dladsc,&found);
//f = fopen("/Users/m5151134/Desktop/commonF_aft.dat", "w");
f = fopen(fname.c_str(), "w");
if(!found){
setmsg_c ( "No segments found in DSK file #." );
sigerr_c ( "SPICE(NODATA)" );
}
//Get Number of Plate
dski02_c ( handle, &dladsc, SPICE_DSK_KWNP,
0, 1, &n, &np );
pd = new int*[np];
pd[0] = new int[np * 3];
for (i = 1; i < np; i++) pd[i] = pd[0] + i * 3;
//Get Number of Vertices
dski02_c ( handle, &dladsc, SPICE_DSK_KWNV,
0, 1, &n, &nv );
vd = new double*[nv];
vd[0] = new double[nv*3];
for (i = 1; i < nv; i++) vd[i] = vd[0] + i * 3;
readPlateData(handle,dladsc);
readVerticesData(handle,dladsc);
dascls_c ( handle );
/*
for (i = 0 ; i < nv ; i++) {
printf("%d %d %d %d %d\n",i,nv,pd[i][0],pd[i][1],pd[i][2]);
}
*/
int fppp=0,fppm=0,fpmp=0,fmpp=0,fpmm=0,fmpm=0,fmmp=0,fmmm=0;
for ( i = 0 ; i < np ; i++) {
for ( int j = 0 ; j < 3 ; j++) {
//printf("check:%d %d %d %d %d\n",i,j,nv,np,pd[i][j]);
double x = vd[pd[i][j]-1][0];
double y = vd[pd[i][j]-1][1];
double z = vd[pd[i][j]-1][2];
//+x+y+z
if (x >= 0 && y >= 0 && z>= 0 && fppp == 0) {
ppp.push_back(i+1);
fppp = 1;
}
//+x+y-z
if (x >= 0 && y >= 0 && z <= 0 && fppm == 0) {
ppm.push_back(i+1);
fppm = 1;
}
//+x-y+z
if (x >= 0 && y <= 0 && z >= 0 && fpmp == 0) {
pmp.push_back(i+1);
fpmp = 1;
}
//-x+y+z
if (x <= 0 && y >= 0 && z >= 0 && fmpp == 0) {
mpp.push_back(i+1);
fmpp = 1;
}
//+x-y-z
if (x >= 0 && y <= 0 && z <= 0 && fpmm == 0) {
pmm.push_back(i+1);
fpmm = 1;
}
//-x+y-z
if (x <= 0 && y >= 0 && z <= 0 && fmpm == 0) {
mpm.push_back(i+1);
fmpm = 1;
}
//-x-y+z
if (x <= 0 && y <= 0 && z >= 0 && fmmp == 0) {
mmp.push_back(i+1);
fmmp = 1;
}
//-x-y-z
if (x <= 0 && y <= 0 && z <= 0 && fmmm == 0) {
mmm.push_back(i+1);
fmmm = 1;
}
}
fppp=0;
fppm=0;
fpmp=0;
fmpp=0;
fpmm=0;
fmpm=0;
fmmp=0;
fmmm=0;
}
commonF = new int*[np];
commonF[0] = new int[np * 3];
for (i = 1; i < np; i++) commonF[i] = commonF[0] + i * 3;
/*
for( i = 0 ; i < np ; i++){
printf("nv:%d np:%d pd0:%d p1:%d p2:%d\n",nv,np,pd[i][0],pd[i][1],pd[i][2]);
}
*/
map<int,set<int> > dict;
for(int i = 0; i < np; ++i){
for(int j = 0; j < 3; ++j){
dict[pd[i][j]].insert(i);
}
}
int *conts = new int[np];
for(int i = 0; i < np; ++i){
conts[i] = 0;
}
for(int i = 0; i < np; ++i){
set<int> ids;
for(int j = 0; j < 3; ++j){
for(set<int>::iterator it = dict[pd[i][j]].begin(); it != dict[pd[i][j]].end(); ++it){
ids.insert( *it );
}
}
int cnt = 0;
int id_array[ids.size()];
for(set<int>::iterator it = ids.begin(); it != ids.end(); ++it){
id_array[cnt++] = *it;
}
for(int j = 0; j < ids.size(); ++j){
int fid = 0;
fid = id_array[j];
for(int k = 0; k < ids.size(); ++k){
int sid = 0;
sid = id_array[k];
if( fid != sid ){
for(int ii = 0; ii < 3; ++ii){
int norme1 = pd[fid][ii];
int norme2 = pd[fid][(ii+1)%3];
for(int jj = 0; jj < 3; ++jj){
int normf1 = pd[sid][jj];
int normf2 = pd[sid][(jj+1)%3];
if( (norme1 == normf1 && norme2 == normf2) || (norme1 == normf2 && norme2 == normf1) ){
if( conts[fid] >= 3 ) continue;
bool ng = false;
for(int kk = 0; kk < conts[fid]; ++kk){
if( commonF[fid][kk] == sid+1 ){
ng = true;
}
}
if( !ng ){
commonF[fid][conts[fid]++] = sid+1;
}
}
}
}
}
}
}
}
//printf("getdata: %d",commonF[0][0]);
fclose(f);
}
void getelm_c ( SpiceInt frstyr,
SpiceInt lineln,
const void * lines,
SpiceDouble * epoch,
SpiceDouble * elems )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
frstyr I Year of earliest representable two-line elements.
lineln I Length of strings in lines array.
lines I A pair of "lines" containing two-line elements.
epoch O The epoch of the elements in seconds past J2000.
elems O The elements converted to SPICE units.
-Detailed_Input
frstyr is the first year possible for two line elements. Since
two line elements allow only two digits for the year, some
conventions must be followed concerning which century the
two digits refer to. frstyr is the year of the earliest
representable elements. The two-digit year is mapped to
the year in the interval from frstyr to frstyr + 99 that
has the same last two digits as the two digit year in the
element set. For example if frstyr is set to 1960 then
the two digit years are mapped as shown in the table
below:
Two-line Maps to
element year
00 2000
01 2001
02 2002
. .
. .
. .
58 2058
59 2059
--------------------
60 1960
61 1961
62 1962
. .
. .
. .
99 1999
Note that if Space Command should decide to represent
years in 21st century as 100 + the last two digits of the
year (for example: 2015 is represented as 115) instead of
simply dropping the first two digits of the year, this
routine will correctly map the year as long as you set
frstyr to some value between 1900 and 1999.
lines is a pair of lines of text that comprise a Space command
``two-line element'' set. lines should be declared
SpiceChar lines[2][lineln];
These text lines should be the same as they are presented
in the two-line element files available from Space
Command (formerly NORAD). Below is an example of a
two-line set for TOPEX.
TOPEX
1 22076U 92052A 97173.53461370 -.00000038 00000-0 10000-3 0 594
2 22076 66.0378 163.4372 0008359 278.7732 81.2337 12.80930736227550
-Detailed_Output
epoch is the epoch of the two line elements supplied via
the input array lines. Epoch is returned in TDB
seconds past J2000.
elems is an array containing the elements from the two line
set supplied via the array lines. The elements are
in units suitable for use by the CSPICE routine
ev2lin_.
Also note that the elements XNDD6O and BSTAR
incorporate the exponential factor present in the
input two line elements in LINES. (See particulars
below.
ELEMS [ 0 ] = XNDT2O in radians/minute**2
ELEMS [ 1 ] = XNDD6O in radians/minute**3
ELEMS [ 2 ] = BSTAR
ELEMS [ 3 ] = XINCL in radians
ELEMS [ 4 ] = XNODEO in radians
ELEMS [ 5 ] = EO
ELEMS [ 6 ] = OMEGAO in radians
ELEMS [ 7 ] = XMO in radians
ELEMS [ 8 ] = XNO in radians/minute
ELEMS [ 9 ] = EPOCH of the elements in seconds
past ephemeris epoch J2000.
-Parameters
None.
-Exceptions
No checking of the inputs is performed in this routine. However, this
routine does call other CSPICE routines. If one of these routines
detects an error it will diagnose it and signal an error.
-Files
You must have loaded a SPICE leapseconds kernel into the
kernel pool prior to caling this routine.
-Particulars
This routine parses a Space Command Two-line element set and returns
the orbital elements properly scaled and in units suitable for use
by other SPICE software. Input elements look like the following
---------------------------------------------------------------------
1 22076U 92052A 97173.53461370 -.00000038 00000-0 10000-3 0 594
2 22076 66.0378 163.4372 0008359 278.7732 81.2337 12.80930736227550
---------------------------------------------------------------------
^
123456789012345678901234567890123456789012345678901234567890123456789
1 2 3 4 5 6
The ``raw'' elements in the first and second lines are marked below.
Note that in several instances exponents and decimal points are
implied. Also note that input units are degrees, degrees/day**n and
revolutions/day.
DAY OF YEAR NDD60 BSTAR
vvvvvvvvvvvv vvvvvv vvvvvv
---------------------------------------------------------------------
1 22076U 92052A 97173.53461370 -.00000038 00000-0 10000-3 0 594
---------------------------------------------------------------------
^^ ^^^^^^^^^^ ^^ ^^
YEAR NDT20 IEXP IBEXP
The ``raw'' elements in the second line are marked below
NODE0 OMEGA N0
vvvvvvvv vvvvvvvv vvvvvvvvvvv
---------------------------------------------------------------------
2 22076 66.0378 163.4372 0008359 278.7732 81.2337 12.80930736227550
---------------------------------------------------------------------
^^^^^^^^ ^^^^^^^ ^^^^^^^^
Inclination Eccentricity M0
This routine extracts these values ``inserts'' the implied
decimal points and exponents and then converts the inputs
to units of radians, radians/minute, radians/minute**2, and
radians/minute**3
-Examples
Suppose you have a set of two-line elements and an array containing
the related geophysical constants necessary to evaluate a state.
The example below shows how you can use this routine together with
the routine EV2LIN to propagate a state to an epoch of interest.
#include <string.h>
#include <stdio.h>
#include "SpiceUsr.h"
SpiceDouble et;
SpiceDouble epoch;
SpiceInt frstyr;
.
.
.
/.
The parameters below will make it easier to make assignments
to the array GEOPHS required by EV2LIN.
J2 --- location of J2
J3 --- location of J3
J4 --- location if J4
KE --- location of KE = sqrt(GM) in eart-radii**1.5/MIN
QO --- location of upper bound of atmospheric model in KM
SO --- location of lower bound of atmospheric model in KM
ER --- location of earth equatorial radius in KM.
AE --- location of distance units/earth radius
./
#define J2 0
#define J3 1
#define J4 2
#define KE 3
#define QO 4
#define SO 5
#define ER 6
#define AE 7
/.
We set the lower bound for the years to be the beginning
of the space age.
./
frstyr = 1957;
/.
Read in the next two lines from the text file that contains
the two-line elements. We assume that file has been opened
properly and that we have set the ``file pointer'' to the
correct location for reading the next set of elements.
./
for ( i = 0; i < 2; i++ )
{
fgets ( line[i], lineln, textfile );
line[i][ strlen(line[i]) ] = '\0';
}
getelm_c ( frstyr, lineln, line, &epoch, elems );
/.
Set up the geophysical quantities. At last check these
were the values used by Space Command.
./
geophs[ J2 ] = 1.082616e-3;
geophs[ J3 ] = -2.53881e-6;
geophs[ J4 ] = -1.65597e-6;
geophs[ KE ] = 7.43669161e-2;
geophs[ QO ] = 120.0;
geophs[ SO ] = 78.0;
geophs[ ER ] = 6378.135;
geophs[ AE ] = 1.0;
/.
Now propagate the state using ev2lin_ to the epoch of
interest.
./
ev2lin_ ( &et, geophs, elems, state );
-Restrictions
The format of the two-line elements suffer from a "millenium"
problem---only two digits are used for the year of the elements. It
is not clear how Space Command will deal with this problem as the
year 2000 comes and goes. We hope that by adjusting the input frstyr
you should be able to use this routine well into the 21st century.
However, since we can't predict how others will resolve the millenium
problem we can't be sure that our approach will be addequate to deal
with the problem.
The approach taken to mapping the two-digit year to the full year is
given by the code below. Here, yr is the integer obtained by parsing
the two-digit year from the first line of the elements.
begyr = (frstyr/100)*100;
year = begyr + yr;
if ( year < frstyr )
{
year += 100;
}
This mapping will be changed if future two-line element
representations make this method of computing the full year
inaccurate.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
W.L. Taber (JPL)
-Version
-CSPICE Version 1.0.1, 15-NOV-2007 (EDW)
Minor edits to example section; the getelm_c call lacked
the 'lineln' argument, the use of 'et' implied a pointer
rather than a value.
-CSPICE Version 1.0.0, 06-AUG-1999 (NJB) (WLT)
-Index_Entries
Parse two-line elements
-&
*/
{ /* Begin getelm_c */
/*
Local constants
*/
#define NELTS 2
/*
Local variables
*/
SpiceChar ** cvalsPtr;
SpiceChar * fCvalsArr;
SpiceInt i;
SpiceInt fCvalsLen;
SpiceStatus status;
/*
Participate in error tracing.
*/
chkin_c ( "getelm_c" );
/*
Check the input line array for null pointer of insufficient string
length.
*/
CHKOSTR ( CHK_STANDARD, "getelm_c", lines, lineln );
/*
Convert the input string array to a Fortran-style string array.
We'll first allocate an array of character pointers to index
the values, initialize this array, and use it to produce
a dynamically allocated array of Fortran-style strings.
*/
cvalsPtr = ( SpiceChar ** ) malloc ( NELTS * sizeof(SpiceChar *) );
if ( cvalsPtr == 0 )
{
setmsg_c ( "Failure on malloc call to create pointer array "
"for line values." );
sigerr_c ( "SPICE(MALLOCFAILED)" );
chkout_c ( "getelm_c" );
return;
}
for ( i = 0; i < NELTS; i++ )
{
cvalsPtr[i] = (SpiceChar *)lines + ( i * lineln );
}
status = C2F_CreateStrArr ( NELTS,
( ConstSpiceChar ** ) cvalsPtr,
&fCvalsLen,
&fCvalsArr );
/* fCvalsArr[2*fCvalsLen] = '\0'; */
if ( status == SPICEFAILURE )
{
free ( cvalsPtr );
setmsg_c ( "C to Fortran string array conversion for `lines' "
"failed." );
sigerr_c ( "SPICE(STRINGCONVERROR)" );
chkout_c ( "getelm_c" );
return;
}
/*
Call the f2c'd routine.
*/
getelm_ ( ( integer * ) &frstyr,
( char * ) fCvalsArr,
( doublereal * ) epoch,
( doublereal * ) elems,
( ftnlen ) fCvalsLen );
/*
Clean up all of our dynamically allocated arrays.
*/
free ( cvalsPtr );
free ( fCvalsArr );
chkout_c ( "getelm_c" );
} /* End getelm_c */
void gfpa_c ( ConstSpiceChar * target,
ConstSpiceChar * illmn,
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.
illmn I Name of the illuminating 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. 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.
Case and leading or trailing blanks are not significant
in the string `target'.
illmn the string name of the illuminating body. This will
normally be "SUN" but the algorithm can use any
ephemeris object
Case and leading or trailing blanks are not significant
in the string `illmn'.
abcorr indicates the aberration corrections to be applied to
the observer-target position 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 allowed aberation 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.
Note that this routine accepts only reception mode
aberration corrections.
Case and leading or trailing blanks are not significant
in the string `abcorr'.
obsrvr is the name of the observing body. 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.
Case and leading or trailing blanks are not significant
in the string `obsrvr'.
relate is a relational operator used to define a constraint on
the phase angle. 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:
">" The phase angle value is greater than the
reference value REFVAL.
"=" The phase angle value is equal to the
reference value REFVAL.
"<" The phase angle value is less than the
reference value REFVAL.
"ABSMAX" The phase angle value is at an absolute
maximum.
"ABSMIN" The phase angle value is at an absolute
minimum.
"LOCMAX" The phase angle value is at a local
maximum.
"LOCMIN" The phase angle value is at a local
minimum.
`relate' may be used to specify an "adjusted" absolute
extremum constraint: this requires the phase angle
to be within a specified offset relative to an
absolute extremum. The argument `adjust' (described
below) is used to specify this offset.
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 and leading or trailing blanks are 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 phase angle. See the discussion of
`relate' above for further information.
The units of `refval' are radians.
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, gfpa_c will
find times when the phase angle is within
`adjust' radians 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 phase angle 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 shorter than any maximal time interval on which the
specified phase angle function is monotone increasing or
decreasing. That is, if the confinement window is
partitioned into alternating intervals on which the
phase angle function is either monotone increasing or
decreasing, `step' must be shorter than any of these
intervals.
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
workspace windows used internally by this routine.
In many cases, it's not necessary to compute an accurate
estimate of how many intervals are needed; rather, the
user can pick a size considerably larger than what's
really required.
However, since excessively large arrays can prevent
applications from compiling, linking, or running
properly, sometimes `nintvls' must be set according to
the actual workspace requirement. A rule of thumb for
the number of intervals needed is
nintvls = 2*n + ( m / step )
where
n is the number of intervals in the confinement
window
m is the measure of the confinement window, in
units of seconds
`step' is the search step size in 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 the window of intervals, contained within the
confinement window `cnfine', on which the specified
phase angle constraint is satisfied.
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 gfpa_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, 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 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 the output SPICE window `result' has insufficient capacity to
contain the number of intervals on which the specified geometric
condition is met, the error will be diagnosed by a routine in
the call tree of this routine. If the result window has size
less than 2, the error SPICE(INVALIDDIMENSION) will be signaled
by this routine.
12) If any input string argument pointer is null, the error
SPICE(NULLPOINTER) will be signaled.
13) If any input string argument is empty, the error
SPICE(EMPTYSTRING) will be signaled.
14) If either input cell has type other than SpiceDouble,
the error SPICE(TYPEMISMATCH) is signaled.
15) An error signals from a routine in the call tree of
this routine for any transmit mode aberration correction.
-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_c.
Kernel data are normally loaded once per program run, NOT every
time this routine is called.
-Particulars
ILLMN OBS
ILLMN as seen * /
from TARG at | /
ET - LT. | /
>|..../< phase angle
| /
. | /
. | /
. * TARG as seen from OBS
SEP . TARG at ET
. /
/
*
This routine determines if the caller-specified constraint
condition on the geometric event (phase angle) 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 searches for
illuminator-target-observer phase angle value events.
Applications that require support for progress reporting,
interrupt handling, non-default step or refinement functions
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
phase angle 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 phase angle
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 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 phase angle 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
phase angle 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 phase angle 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,
illumination source, 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. 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.
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 December 1, 2006 UTC to
January 31, 2007 UTC for which the sun-moon-earth configuration
phase angle satisfies the relation conditions with respect to a
reference value of .57598845 radians (the phase angle at
January 1, 2007 00:00:00.000 UTC, 33.001707 degrees). Also
determine the time windows corresponding to the local maximum and
minimum phase angles, and the absolute maximum and minimum phase
angles during the search interval. The configuration defines the
sun as the illuminator, the moon as the target, and the earth as
the observer.
#include <stdio.h>
#include "SpiceUsr.h"
#define TIMFMT "YYYY MON DD HR:MN:SC.###"
#define NINTVL 5000
#define TIMLEN 41
#define NLOOPS 7
int main()
{
/.
Local variables
./
SpiceChar begstr [ TIMLEN ];
SpiceChar endstr [ TIMLEN ];
SPICEDOUBLE_CELL ( cnfine, 2 );
SPICEDOUBLE_CELL ( result, NINTVL*2 );
SpiceDouble adjust;
SpiceDouble et0;
SpiceDouble et1;
SpiceDouble phaseq;
SpiceDouble refval;
SpiceDouble start;
SpiceDouble step;
SpiceDouble stop;
SpiceInt i;
SpiceInt j;
/.
Define the values for target, observer, illuminator, and
aberration correction.
./
ConstSpiceChar * target = "moon";
ConstSpiceChar * illmn = "sun";
ConstSpiceChar * abcorr = "lt+s";
ConstSpiceChar * obsrvr = "earth";
ConstSpiceChar * relate [NLOOPS] = { "=",
"<",
">",
"LOCMIN",
"ABSMIN",
"LOCMAX",
"ABSMAX",
};
/.
Load kernels.
./
furnsh_c ( "standard.tm" );
/.
Store the time bounds of our search interval in
the confinement window.
./
str2et_c ( "2006 DEC 01", &et0 );
str2et_c ( "2007 JAN 31", &et1 );
wninsd_c ( et0, et1, &cnfine );
/.
Search using a step size of 1 day (in units of seconds).
The reference value is 0.57598845 radians. We're not using the
adjustment feature, so we set ADJUST to zero.
./
step = spd_c();
refval = 0.57598845;
adjust = 0.0;
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.
./
gfpa_c ( target, illmn, abcorr, obsrvr,
relate[j], refval, adjust, step,
NINTVL, &cnfine, &result );
/.
Display the results.
./
if ( wncard_c(&result) == 0 )
{
printf ( "Result window is empty.\n\n" );
}
else
{
for ( i = 0; i < wncard_c(&result); i++ )
{
/.
Fetch the endpoints of the Ith interval
of the result window.
./
wnfetd_c ( &result, i, &start, &stop );
phaseq = phaseq_c ( start, target, illmn, obsrvr, abcorr );
timout_c ( start, TIMFMT, TIMLEN, begstr );
printf ( "Start time = %s %16.9f\n", begstr, phaseq );
phaseq = phaseq_c ( stop, target, illmn, obsrvr, abcorr );
timout_c ( stop, TIMFMT, TIMLEN, endstr );
printf ( "Stop time = %s %16.9f\n", endstr, phaseq );
}
printf("\n");
}
}
return ( 0 );
}
The program outputs:
Relation condition: =
Start time = 2006 DEC 02 13:31:34.414 0.575988450
Stop time = 2006 DEC 02 13:31:34.414 0.575988450
Start time = 2006 DEC 07 14:07:55.470 0.575988450
Stop time = 2006 DEC 07 14:07:55.470 0.575988450
Start time = 2006 DEC 31 23:59:59.997 0.575988450
Stop time = 2006 DEC 31 23:59:59.997 0.575988450
Start time = 2007 JAN 06 08:16:25.512 0.575988450
Stop time = 2007 JAN 06 08:16:25.512 0.575988450
Start time = 2007 JAN 30 11:41:32.557 0.575988450
Stop time = 2007 JAN 30 11:41:32.557 0.575988450
Relation condition: <
Start time = 2006 DEC 02 13:31:34.414 0.575988450
Stop time = 2006 DEC 07 14:07:55.470 0.575988450
Start time = 2006 DEC 31 23:59:59.997 0.575988450
Stop time = 2007 JAN 06 08:16:25.512 0.575988450
Start time = 2007 JAN 30 11:41:32.557 0.575988450
Stop time = 2007 JAN 31 00:00:00.000 0.468279091
Relation condition: >
Start time = 2006 DEC 01 00:00:00.000 0.940714974
Stop time = 2006 DEC 02 13:31:34.414 0.575988450
Start time = 2006 DEC 07 14:07:55.470 0.575988450
Stop time = 2006 DEC 31 23:59:59.997 0.575988450
Start time = 2007 JAN 06 08:16:25.512 0.575988450
Stop time = 2007 JAN 30 11:41:32.557 0.575988450
Relation condition: LOCMIN
Start time = 2006 DEC 05 00:16:50.317 0.086121423
Stop time = 2006 DEC 05 00:16:50.317 0.086121423
Start time = 2007 JAN 03 14:18:31.977 0.079899769
Stop time = 2007 JAN 03 14:18:31.977 0.079899769
Relation condition: ABSMIN
Start time = 2007 JAN 03 14:18:31.977 0.079899769
Stop time = 2007 JAN 03 14:18:31.977 0.079899769
Relation condition: LOCMAX
Start time = 2006 DEC 20 14:09:10.392 3.055062862
Stop time = 2006 DEC 20 14:09:10.392 3.055062862
Start time = 2007 JAN 19 04:27:54.600 3.074603891
Stop time = 2007 JAN 19 04:27:54.600 3.074603891
Relation condition: ABSMAX
Start time = 2007 JAN 19 04:27:54.600 3.074603891
Stop time = 2007 JAN 19 04:27:54.600 3.074603891
-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.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
E.D. Wright (JPL)
-Version
-CSPICE Version 1.0.0, 15-JUL-2014 (EDW) (NJB)
-Index_Entries
GF phase angle search
-&
*/
{ /* Begin gfpa_c */
/*
Static local variables
*/
static SpiceInt nw = SPICE_GF_NWPA;
/*
Local variables
*/
doublereal * work;
SpiceInt nBytes;
/*
Participate in error tracing.
*/
if ( return_c() )
{
return;
}
chkin_c ( "gfpa_c" );
/*
Make sure cell data types are d.p.
*/
CELLTYPECHK2 ( CHK_STANDARD, "gfpa_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, "gfpa_c", target );
CHKFSTR ( CHK_STANDARD, "gfpa_c", illmn );
CHKFSTR ( CHK_STANDARD, "gfpa_c", abcorr );
CHKFSTR ( CHK_STANDARD, "gfpa_c", obsrvr );
CHKFSTR ( CHK_STANDARD, "gfpa_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 (1)." );
errint_c ( "#", nintvls );
sigerr_c ( "SPICE(VALUEOUTOFRANGE)" );
chkout_c ( "gfpa_c" );
return;
}
/*
Allocate the workspace.
We have `nw' "doublereal" cells, each having cell size 2*nintvls.
Each cell also has a control area containing SPICE_CELL_CTRLSZ
double precision values.
*/
nintvls = nintvls * 2;
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(MALLOCFAILURE)" );
chkout_c ( "gfpa_c" );
return;
}
/*
Let the f2'd routine do the work.
*/
gfpa_ ( ( char * ) target,
( char * ) illmn,
( 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(illmn),
( 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 ( "gfpa_c" );
} /* End gfpa_c */
void dasac_c ( SpiceInt handle,
SpiceInt n,
SpiceInt buflen,
const void * buffer )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
handle I DAS handle of a file opened with write access.
n I Number of comments to put into the comment area.
buflen I Line length associated with buffer.
buffer I Buffer of lines to be put into the comment area.
-Detailed_Input
handle The file handle of a binary DAS file which has been
opened with write access.
n The number of strings in buffer that are to be
appended to the comment area of the binary DAS file
attached to handle.
buflen is the common length of the strings in buffer, including the
terminating nulls.
buffer A buffer containing comments which are to be added
to the comment area of the binary DAS file attached
to handle. buffer should be declared as follows:
ConstSpiceChar buffer [n][buflen]
Each string in buffer is null-terminated.
-Detailed_Output
None.
-Parameters
None.
-Exceptions
1) If the number of comments to be added is not positive, the
error SPICE(INVALIDARGUMENT) will be signaled.
2) If a non-null, non printing ASCII character is encountered in the
comments, the error SPICE(ILLEGALCHARACTER) will be
signaled.
3) If the binary DAS file attached to handle is not open for
write access, an error will be signaled by a routine called
by this routine.
4) If the input buffer pointer is null, the error SPICE(NULLPOINTER)
will be signaled.
5) If the input buffer string length buflen is not at least 2,
the error SPICE(STRINGTOOSHORT) will be signaled.
-Files
See argument handle in Detailed_Input.
-Particulars
Binary DAS files contain a data area which is reserved for storing
annotations or descriptive textual information about the data
contained in a file. This area is referred to as the "comment
area" of the file. The comment area of a DAS file is a line
oriented medium for storing textual information. The comment
area preserves any leading or embedded white space in the line(s)
of text which are stored so that the appearance of the
information will be unchanged when it is retrieved (extracted) at
some other time. Trailing blanks, however, are NOT preserved,
due to the way that character strings are represented in
standard Fortran 77.
This routine will take a buffer of text lines and add (append)
them to the comment area of a binary DAS file. If there are no
comments in the comment area of the file, then space will be
allocated and the text lines in buffer will then placed into the
comment area. The text lines may contain only printable ASCII
characters (decimal values 32 - 126).
There is no maximum length imposed on the significant portion
of a text line that may be placed into the comment area of a
DAS file. The maximum length of a line stored in the comment
area should be reasonable, however, so that they may be easily
extracted. A good value for this would be 255 characters, as
this can easily accommodate "screen width" lines as well as
long lines which may contain some other form of information.
-Examples
Let
handle be the handle for a DAS file which has been opened
with write access.
n be the number of lines of text to be added to the
comment area of the binary DAS file attached to
handle.
BUFLEN be the declared line length of the buffer.
buffer is a list of text lines to be added to the comment
area of the binary DAS file attached to handle.
The call
dasac_c ( handle, n, BUFLEN, buffer );
will append the first n line(s) in buffer to the comment area
of the binary DAS file attached to handle.
-Restrictions
1) This routine uses constants that are specific to the ASCII
character sequence. The results of using this routine with
a different character sequence are unpredictable.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
K.R. Gehringer (JPL)
-Version
-CSPICE Version 1.1.0, 02-MAR-2003 (NJB)
Added error check in wrapper for non-positive
buffer line count.
-CSPICE Version 1.0.0, 25-FEB-2003 (NJB) (KRG)
-Index_Entries
add comments to a binary das file
append comments to a das file comment area
-&
*/
{ /* Begin dasac_c */
/*
Local variables
*/
SpiceChar * fCvalsArr;
SpiceInt fCvalsLen;
/*
Participate in error tracing.
*/
if ( return_c() )
{
return;
}
chkin_c ( "dasac_c" );
/*
Check the line count of the input buffer.
*/
if ( n < 1 )
{
setmsg_c ( "Comment buffer line count n = #; must be positive." );
errint_c ( "#", n );
sigerr_c ( "SPICE(INVALIDARGUMENT)" );
chkout_c ( "dasac_c" );
return;
}
/*
Check the input buffer for null pointer or short lines.
*/
CHKOSTR ( CHK_STANDARD, "dasac_c", buffer, buflen );
/*
Map the input buffer to a Fortran-style buffer.
*/
C2F_MapStrArr ( "dasac_c", n, buflen, buffer, &fCvalsLen, &fCvalsArr );
if ( failed_c() )
{
chkout_c ( "dasac_c" );
return;
}
/*
Call the f2c'd routine.
*/
dasac_ ( ( integer * ) &handle,
( integer * ) &n,
( char * ) fCvalsArr,
( ftnlen ) fCvalsLen );
/*
Free the dynamically allocated array.
*/
free ( fCvalsArr );
chkout_c ( "dasac_c" );
} /* End dasac_c */
void repmi_c ( ConstSpiceChar * in,
ConstSpiceChar * marker,
SpiceInt value,
SpiceInt lenout,
SpiceChar * out )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
in I Input string.
marker I Marker to be replaced.
value I Replacement value.
lenout I Available space in output string.
out O Output string.
MAXLI P Maximum length of an integer.
-Detailed_Input
in is an arbitrary character string.
marker is an arbitrary character string. The first occurrence
of marker in the input string is to be replaced by value.
Leading and trailing blanks in marker are NOT significant.
In particular, no substitution is performed if marker
is blank.
value is an arbitrary integer.
lenout is 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 should be at least x + 1.
-Detailed_Output
out is the string obtained by substituting the text
representation of value for the first occurrence
of marker in the input string.
out and in must be identical or disjoint.
-Parameters
MAXLI is the maximum expected length of the text
representation of an integer. 11 characters are
sufficient to hold any integer whose absolute
value is less than 10 billion.
This routine assumes that the input integer
is such that its string representation contains
no more than MAXLI characters.
-Files
None.
-Exceptions
1) The error SPICE(NULLPOINTER) is signaled if any of
the input or output string pointers is null.
2) If the marker string is blank or empty, this routine leaves
the input string unchanged, except that trailing blanks
will be trimmed. This case is not considered an error.
3) If the output string is too short to accommodate a terminating
null character, the error SPICE(STRINGTOOSHORT) is signaled.
4) If out does not have sufficient length to accommodate the
result of the substitution, the result will be truncated on
the right.
-Particulars
This is one of a family of related routines for inserting values
into strings. They are typically to construct messages that
are partly fixed, and partly determined at run time. For example,
a message like
"Fifty-one pictures were found in directory [USER.DATA]."
might be constructed from the fixed string
"#1 pictures were found in directory #2."
by the calls
#include "SpiceUsr.h"
.
.
.
#define LENOUT 81
.
.
.
repmct_c ( string, "#1", 51, 'c', LENOUT, string );
repmc_c ( string, "#2", "[USER.DATA]", LENOUT, string );
which substitute the cardinal text "Fifty-one" and the character
string "[USER.DATA]" for the markers "#1" and "#2" respectively.
The complete list of routines is shown below.
repmc_c ( Replace marker with character string value )
repmd_c ( Replace marker with double precision value )
repmf_c ( Replace marker with formatted d.p. value )
repmi_c ( Replace marker with integer value )
repmct_c ( Replace marker with cardinal text )
repmot_c ( Replace marker with ordinal text )
-Examples
1. Let
in == "Invalid operation value. The value was <opcode>."
Then following the call,
#include "SpiceUsr.h"
.
.
.
#define LENOUT 201
.
.
.
repmi_c ( in, "<opcode>", 5, LENOUT, outstr );
outstr contains the string:
"Invalid operation value. The value was 5."
2. Let
in == "Left endpoint exceeded right endpoint. "
"The left endpoint was: XX. The right "
"endpoint was: XX."
Then following the call,
#include "SpiceUsr.h"
.
.
.
#define LENOUT 201
.
.
.
repmi_c ( in, " XX ", 5, LENOUT, out );
out is
"Left endpoint exceeded right endpoint. The left "
"endpoint was: 5. The right endpoint was: XX."
3. Let
num == 23
chance == "fair"
score == 4.665
Then following the sequence of calls,
#include "SpiceUsr.h"
.
.
.
#define LENOUT 201
.
.
.
repmi_c ( "There are & routines that have a "
"& chance of meeting your needs."
"The maximum score was &.",
"&",
num,
LENOUT,
msg );
repmc_c ( msg, marker, chance, LENOUT, msg );
repmf_c ( msg, marker, score, 4, 'f', LENOUT, msg );
msg is
"There are 23 routines that have a fair chance of "
"meeting your needs. The maximum score was 4.665."
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
I.M. Underwood (JPL)
-Version
-CSPICE Version 1.0.0, 14-AUG-2002 (NJB) (IMU)
-Index_Entries
replace marker with integer
-&
*/
{ /* Begin repmi_c */
/*
Local variables
*/
ConstSpiceChar * markPtr;
/*
Use discovery check-in.
Make sure no string argument pointers are null.
*/
CHKPTR( CHK_DISCOVER, "repmi_c", in );
CHKPTR( CHK_DISCOVER, "repmi_c", marker );
CHKPTR( CHK_DISCOVER, "repmi_c", out );
/*
If the output string can't hold a terminating null character,
we can't proceed.
*/
if ( lenout < 1 )
{
chkin_c ( "repmi_c" );
setmsg_c ( "String length lenout must be >= 1; actual "
"value = #." );
errint_c ( "#", lenout );
sigerr_c ( "SPICE(STRINGTOOSHORT)" );
chkout_c ( "repmi_c" );
return;
}
/*
If the output string has no room for data characters, we simply
terminate the string.
*/
if ( lenout == 1 )
{
out[0] = NULLCHAR;
return;
}
/*
If the input string has zero length, the output is empty as well.
*/
if ( in[0] == NULLCHAR )
{
out[0] = NULLCHAR;
return;
}
/*
If the marker is empty, pass a blank marker to the f2c'd routine.
Otherwise, pass in the marker.
*/
if ( marker[0] == NULLCHAR )
{
markPtr = " ";
}
else
{
markPtr = marker;
}
/*
Simply call the f2c'd routine.
*/
repmi_ ( ( char * ) in,
( char * ) markPtr,
( integer * ) &value,
( char * ) out,
( ftnlen ) strlen(in),
( ftnlen ) strlen(markPtr),
( ftnlen ) lenout-1 );
/*
Convert the output string from Fortran to C style.
*/
F2C_ConvertStr ( lenout, out );
} /* End repmi_c */
void mxmg_c ( const void * m1,
const void * m2,
SpiceInt nrow1,
SpiceInt ncol1,
SpiceInt ncol2,
void * mout )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
m1 I nrow1 X ncol1 double precision matrix.
m2 I ncol1 X ncol2 double precision matrix.
nrow1 I Row dimension of m1 (and also mout).
ncol1 I Column dimension of m1 and row dimension of m2.
ncol2 I Column dimension of m2 (and also mout).
mout O nrow1 X ncol2 double precision matrix.
-Detailed_Input
m1 is any double precision matrix of arbitrary size.
m2 is any double precision matrix of arbitrary size.
The number of rows in m2 must match the number of
columns in m1.
nrow1 is the number of rows in both m1 and mout.
ncol1 is the number of columns in m1 and (by necessity)
the number of rows of m2.
ncol2 is the number of columns in both m2 and mout.
-Detailed_Output
mout
mout is the product matrix defined by
mout = (m1) x (m2)
mout is a double precision matrix of dimension nrow1 x
ncol2.
mout may overwrite m1 or m2. Note that this capability
does not exist in the Fortran version of SPICELIB; in the
Fortran version, the output must not overwrite either
input.
-Parameters
None.
-Exceptions
1) If dynamic allocation of memory fails, the error
SPICE(MEMALLOCFAILED) is signalled.
-Files
None.
-Particulars
The code reflects precisely the following mathematical expression
For each value of the subscript i from 1 to nrow1, and j from 1
to ncol2:
mout(i,j) = Summation from k=1 to ncol1 of m1(i,k) * m2(k,j)
-Examples
Let
m1 = | 1.0 4.0 | and m2 = | 1.0 3.0 5.0 |
| | |
| 2.0 5.0 | | 2.0 4.0 6.0 |
| |
| 3.0 6.0 |
and
nrow1 = 3
ncol1 = 2
ncol2 = 3
Then the call
mxmg ( m1, m2, nrow1, ncol1, ncol2, mout );
produces the matrix
mout = | 9.0 19.0 29.0 |
| |
| 12.0 26.0 40.0 |
| |
| 15.0 33.0 51.0 |
-Restrictions
1) No error checking is performed to prevent numeric overflow or
underflow.
2) No error checking performed to determine if the input and
output matrices have, in fact, been correctly dimensioned.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
W.M. Owen (JPL)
-Version
-CSPICE Version 1.1.2, 16-JAN-2008 (EDW)
Corrected typos in header titles:
Detailed Input to Detailed_Input
Detailed Output to Detailed_Output
-CSPICE Version 1.1.1, 10-NOV-2006 (EDW)
Added Parameters section header.
-CSPICE Version 1.1.0, 28-AUG-2001 (NJB)
Const-qualified input arrays.
-CSPICE Version 1.0.0, 16-APR-1999 (NJB)
-Index_Entries
matrix times matrix n-dimensional_case
-&
*/
{ /* Begin mxmg_c */
/*
Local macros
We'd like to be able to refer to the elements of the input and output
matrices using normal subscripts, for example, m1[2][3]. Since the
compiler doesn't know how to compute index offsets for the array
arguments, which have user-adjustable size, we must compute the
offsets ourselves. To make syntax a little easier to read (we hope),
we'll use macros to do the computations.
The macro INDEX(width, i,j) computes the index offset from the array
base of the element at position [i][j] in a 2-dimensional matrix
having the number of columns indicated by width. For example, if
the input matrix m1 has 2 rows and 3 columns, the element at position
[0][1] would be indicated by
m1[ INDEX(3,0,1) ]
*/
#define INDEX( width, row, col ) ( (row)*(width) + (col) )
/*
Local variables
*/
SpiceDouble innerProduct;
SpiceDouble *tmpmat;
SpiceDouble *loc_m1;
SpiceDouble *loc_m2;
SpiceInt col;
SpiceInt nelts;
SpiceInt row;
SpiceInt i;
size_t size;
/*
Allocate space for a temporary copy of the output matrix, which
has nrow1 rows and ncol2 columns.
*/
nelts = nrow1 * ncol2;
size = (size_t) ( nelts * sizeof(SpiceDouble) );
tmpmat = (SpiceDouble *) malloc ( size );
if ( tmpmat == (SpiceDouble *)0 )
{
chkin_c ( "mxmg_c" );
setmsg_c ( "An attempt to create a temporary matrix failed." );
sigerr_c ( "SPICE(MEMALLOCFAILED)" );
chkout_c ( "mxmg_c" );
return;
}
/*
Cast the input pointers to pointers to SpiceDoubles. Note: the
original variables are pointers to void so that callers may
supply the array names as arguments without casting them to
SpiceDoubles. The naked array name is considered by the compiler
to be an incompatible pointer type with (SpiceDouble *), so we
can't simply declare the arguments to be (SpiceDouble *). On the
other hand, every pointer type can be cast to (void *).
*/
loc_m1 = (SpiceDouble *) m1;
loc_m2 = (SpiceDouble *) m2;
/*
Compute the product. The matrix element at position (row,col) is
the inner product of the row of m1 having index row and the
column of m2 having index col. We compute index offsets using
the macro INDEX.
*/
for ( row = 0; row < nrow1; row++ )
{
for ( col = 0; col < ncol2; col++ )
{
innerProduct = 0.0;
for ( i = 0; i < ncol1; i++ )
{
innerProduct += loc_m1[ INDEX(ncol1, row, i ) ]
* loc_m2[ INDEX(ncol2, i, col) ];
}
tmpmat [ INDEX( ncol2, row, col ) ] = innerProduct;
}
}
/*
Move the result from tmpmat into mout.
*/
MOVED ( tmpmat, nelts, mout );
/*
Free the temporary matrix.
*/
free ( tmpmat );
} /* End mxmg_c */
int main(int ac, char** av)
{
/* Constants */
#define PBUFSIZ 10000
#define FILSIZ 256
/* Local variables */
SpiceBoolean found;
SpiceChar dsk [ FILSIZ ];
SpiceDLADescr dladsc;
SpiceDouble normal [3];
SpiceDouble verts [3][3];
SpiceDouble BoundRadius;
SpiceInt handle;
SpiceInt i;
SpiceInt j;
SpiceInt n;
SpiceInt np;
SpiceInt nread;
SpiceInt nv;
SpiceInt nvtx;
SpiceInt plates[PBUFSIZ][3];
SpiceInt plix;
SpiceInt remain;
SpiceInt start;
int iAc;
int doMdl = 1;
/* Prompt for name of DSK and open file for reading. */
*dsk = '\0';
for (iAc=1; iAc<ac; ++iAc) {
if ( strcmp(av[iAc], "--wrl") ) {
strncpy(dsk,av[1],FILSIZ);
continue;
} else {
doMdl = 0;
}
}
if ( ! *dsk) {
if ( doMdl ) {
prompt_c ( "### Enter DSK (*.bds) filepath > ", FILSIZ, dsk );
} else {
fprintf( stderr, "### Enter DSK (*.bds) filepath > " );
prompt_c ( "", FILSIZ, dsk );
}
}
dasopr_c ( dsk, &handle );
dlabfs_c ( handle, &dladsc, &found );
if ( !found )
{
setmsg_c ( "No segment found in file #." );
errch_c ( "#", dsk );
sigerr_c ( "SPICE(NOSEGMENT)" );
}
/* Get segment vertex and plate counts. */
dskz02_c ( handle, &dladsc, &nv, &np );
/*******************************************************************/
if ( doMdl ) {
printf( "\
### File: %s\n\
Component DSK\n\
PolygonMesh\n\
FaceColor %%255255255\n\
SmoothShading No\n\
BackfaceCullable Yes\n\
Translucency 0.5\n\
Specularity 0.59375000\n\
Shininess 76.000000\n\
\n\
NumVerts %d\n\
Data\n", dsk, nv );
} else {
void insrti_c ( SpiceInt item,
SpiceCell * set )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
item I Item to be inserted.
set I/O Insertion set.
-Detailed_Input
item is an item which is to be inserted into the
specified set. item may or may not already
be an element of the set.
set is a CSPICE set. set must be declared as an integer
SpiceCell.
On input, set may or may not contain the input item
as an element.
-Detailed_Output
set on output contains the union of the input set and
the singleton set containing the input item.
-Parameters
None.
-Exceptions
1) If the input set argument is a SpiceCell of type other than
integer, the error SPICE(TYPEMISMATCH) is signaled.
2) If the insertion of the element into the set causes an excess
of elements, the error SPICE(SETEXCESS) is signaled.
3) If the input set argument does not qualify as a CSPICE set,
the error SPICE(NOTASET) will be signaled. CSPICE sets have
their data elements sorted in increasing order and contain
no duplicate data elements.
-Files
None.
-Particulars
None.
-Examples
1) In the following example, the NAIF ID code of Pluto is removed from
the integer set planets and inserted into the integer set
asteroids.
#include "SpiceUsr.h"
.
.
.
/.
Declare the sets with maximum number of elements MAXSIZ.
./
SPICEINT_CELL ( planets, MAXSIZ );
SPICEINT_CELL ( asteroids, MAXSIZ );
.
.
.
removi_c ( 999, &planets );
insrti_c ( 999, &asteroids );
If 999 is not an element of planets, then the contents of
planets are not changed. Similarly, if 999 is already an
element of asteroids, the contents of asteroids remain unchanged.
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
C.A. Curzon (JPL)
W.L. Taber (JPL)
I.M. Underwood (JPL)
-Version
-CSPICE Version 2.0.0, 01-NOV-2005 (NJB)
Long error message was updated to include size of
set into which insertion was attempted.
-CSPICE Version 1.0.0, 07-AUG-2002 (NJB) (CAC) (WLT) (IMU)
-Index_Entries
insert an item into an integer set
-&
*/
{
/*
local variables
*/
SpiceBoolean inSet;
SpiceInt i;
SpiceInt * idata;
SpiceInt loc;
/*
Use discovery check-in.
*/
/*
Make sure we're working with an integer cell.
*/
CELLTYPECHK ( CHK_DISCOVER, "insrti_c", SPICE_INT, set );
idata = (SpiceInt *) (set->data);
/*
Make sure the cell is really a set.
*/
CELLISSETCHK ( CHK_DISCOVER, "insrti_c", set );
/*
Initialize the set if necessary.
*/
CELLINIT ( set );
/*
Is the item already in the set? If not, it needs to be inserted.
*/
loc = lstlei_c ( item, set->card, idata );
inSet = ( loc > -1 ) && ( item == idata[loc] );
if ( inSet )
{
return;
}
/*
It's an error if the set has no room left.
*/
if ( set->card == set->size )
{
chkin_c ( "insrti_c" );
setmsg_c ( "An element could not be inserted into the set "
"due to lack of space; set size is #." );
errint_c ( "#", set->size );
sigerr_c ( "SPICE(SETEXCESS)" );
chkout_c ( "insrti_c" );
return;
}
/*
Make room by moving the items that come after item in the set.
Insert the item after index loc.
*/
for ( i = (set->card); i > loc+1; i-- )
{
idata[i] = idata[i-1];
}
idata[loc+1] = item;
/*
Increment the set's cardinality.
*/
(set->card) ++;
/*
Sync the set.
*/
zzsynccl_c ( C2F, set );
}
void npedln_c ( SpiceDouble a,
SpiceDouble b,
SpiceDouble c,
ConstSpiceDouble linept[3],
ConstSpiceDouble linedr[3],
SpiceDouble pnear[3],
SpiceDouble * dist )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
a I Length of ellipsoid's semi-axis in the x direction
b I Length of ellipsoid's semi-axis in the y direction
c I Length of ellipsoid's semi-axis in the z direction
linept I Point on line
linedr I Direction vector of line
pnear O Nearest point on ellipsoid to line
dist O Distance of ellipsoid from line
-Detailed_Input
a,
b,
c are the lengths of the semi-axes of a triaxial
ellipsoid which is centered at the origin and
oriented so that its axes lie on the x-, y- and
z- coordinate axes. a, b, and c are the lengths of
the semi-axes that point in the x, y, and z
directions respectively.
linept
linedr are, respectively, a point and a direction vector
that define a line. The line is the set of vectors
linept + t * linedr
where t is any real number.
-Detailed_Output
pnear is the point on the ellipsoid that is closest to
the line, if the line doesn't intersect the
ellipsoid.
If the line intersects the ellipsoid, pnear will
be a point of intersection. If linept is outside
of the ellipsoid, pnear will be the closest point
of intersection. If linept is inside the
ellipsoid, pnear will not necessarily be the
closest point of intersection.
dist is the distance of the line from the ellipsoid.
This is the minimum distance between any point on
the line and any point on the ellipsoid.
If the line intersects the ellipsoid, dist is zero.
-Parameters
None.
-Exceptions
If this routine detects an error, the output arguments nearp and
dist are not modified.
1) If the length of any semi-axis of the ellipsoid is
non-positive, the error SPICE(INVALIDAXISLENGTH) is signaled.
2) If the line's direction vector is the zero vector, the error
SPICE(ZEROVECTOR) is signaled.
3) If the length of any semi-axis of the ellipsoid is zero after
the semi-axis lengths are scaled by the reciprocal of the
magnitude of the longest semi-axis and then squared, the error
SPICE(DEGENERATECASE) is signaled.
4) If the input ellipsoid is extremely flat or needle-shaped
and has its shortest axis close to perpendicular to the input
line, numerical problems could cause this routine's algorithm
to fail, in which case the error SPICE(DEGENERATECASE) is
signaled.
-Files
None.
-Particulars
For any ellipsoid and line, if the line does not intersect the
ellipsoid, there is a unique point on the ellipsoid that is
closest to the line. Therefore, the distance dist between
ellipsoid and line is well-defined. The unique line segment of
length dist that connects the line and ellipsoid is normal to
both of these objects at its endpoints.
If the line intersects the ellipsoid, the distance between the
line and ellipsoid is zero.
-Examples
1) We can find the distance between an instrument optic axis ray
and the surface of a body modelled as a tri-axial ellipsoid
using this routine. If the instrument position and pointing
unit vector in body-fixed coordinates are
linept = ( 1.0e6, 2.0e6, 3.0e6 )
and
linedr = ( -4.472091234e-1
-8.944182469e-1,
-4.472091234e-3 )
and the body semi-axes lengths are
a = 7.0e5
b = 7.0e5
c = 6.0e5,
then the call to npedln_c
npedln_c ( a, b, c, linept, linedr, pnear, &dist );
yields a value for pnear, the nearest point on the body to
the optic axis ray, of
( -.16333110792340931E+04,
-.32666222157820771E+04,
.59999183350006724E+06 )
and a value for dist, the distance to the ray, of
.23899679338299707E+06
(These results were obtained on a PC-Linux system under gcc.)
In some cases, it may not be clear that the closest point
on the line containing an instrument boresight ray is on
the boresight ray itself; the point may lie on the ray
having the same vertex as the boresight ray and pointing in
the opposite direction. To rule out this possibility, we
can make the following test:
/.
Find the difference vector between the closest point
on the ellipsoid to the line containing the boresight
ray and the boresight ray's vertex. Find the
angular separation between this difference vector
and the boresight ray. If the angular separation
does not exceed pi/2, we have the nominal geometry.
Otherwise, we have an error.
./
vsub_c ( pnear, linept, diff );
sep = vsep_c ( diff, linedr );
if ( sep <= halfpi_c() )
{
[ perform normal processing ]
}
else
{
[ handle error case ]
}
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
-Version
-CSPICE Version 1.1.0, 01-JUN-2010 (NJB)
Added touchd_ calls to tests for squared, scaled axis length
underflow. This forces rounding to zero in certain cases where
it otherwise might not occur due to use of extended registers.
-CSPICE Version 1.0.1, 06-DEC-2002 (NJB)
Outputs shown in header example have been corrected to
be consistent with those produced by this routine.
-CSPICE Version 1.0.0, 03-SEP-1999 (NJB)
-Index_Entries
distance between line and ellipsoid
distance between line of sight and body
nearest point on ellipsoid to line
-&
*/
{ /* Begin npedln_c */
/*
Local variables
*/
SpiceBoolean found [2];
SpiceBoolean ifound;
SpiceBoolean xfound;
SpiceDouble oppdir [3];
SpiceDouble mag;
SpiceDouble normal [3];
SpiceDouble prjpt [3];
SpiceDouble prjnpt [3];
SpiceDouble pt [2][3];
SpiceDouble scale;
SpiceDouble scla;
SpiceDouble scla2;
SpiceDouble sclb;
SpiceDouble sclb2;
SpiceDouble sclc;
SpiceDouble sclc2;
SpiceDouble sclpt [3];
SpiceDouble udir [3];
SpiceEllipse cand;
SpiceEllipse prjel;
SpiceInt i;
SpicePlane candpl;
SpicePlane prjpl;
/*
Static variables
*/
/*
Participate in error tracing.
*/
chkin_c ( "npedln_c" );
/*
The algorithm used in this routine has two parts. The first
part handles the case where the input line and ellipsoid
intersect. Our procedure is simple in that case; we just
call surfpt_c twice, passing it first one ray determined by the
input line, then a ray pointing in the opposite direction.
The second part of the algorithm handles the case where surfpt_c
doesn't find an intersection.
Finding the nearest point on the ellipsoid to the line, when the
two do not intersect, is a matter of following four steps:
1) Find the points on the ellipsoid where the surface normal
is normal to the line's direction. This set of points is
an ellipse centered at the origin. The point we seek MUST
lie on this `candidate' ellipse.
2) Project the candidate ellipse onto a plane that is normal
to the line's direction. This projection preserves
distance from the line; the nearest point to the line on
this new ellipse is the projection of the nearest point to
the line on the candidate ellipse, and these two points are
exactly the same distance from the line. If computed using
infinite-precision arithmetic, this projection would be
guaranteed to be non-degenerate as long as the input
ellipsoid were non-degenerate. This can be verified by
taking the inner product of the scaled normal to the candidate
ellipse plane and the line's unitized direction vector
(these vectors are called normal and udir in the code below);
the inner product is strictly greater than 1 if the ellipsoid
is non-degenerate.
3) The nearest point on the line to the projected ellipse will
be contained in the plane onto which the projection is done;
we find this point and then find the nearest point to it on
the projected ellipse. The distance between these two points
is the distance between the line and the ellipsoid.
4) Finally, we find the point on the candidate ellipse that was
projected to the nearest point to the line on the projected
ellipse that was found in step 3. This is the nearest point
on the ellipsoid to the line.
Glossary of Geometric Variables
a,
b,
c Input ellipsoid's semi-axis lengths.
point Point of intersection of line and ellipsoid
if the intersection is non-empty.
candpl Plane containing candidate ellipse.
normal Normal vector to the candidate plane candpl.
cand Candidate ellipse.
linept,
linedr, Point and direction vector on input line.
udir Unitized line direction vector.
prjpl Projection plane; the candidate ellipse is
projected onto this plane to yield prjel.
prjel Projection of the candidate ellipse cand onto
the projection plane prjel.
prjpt Projection of line point.
prjnpt Nearest point on projected ellipse to
projection of line point.
pnear Nearest point on ellipsoid to line.
*/
/*
We need a valid normal vector.
*/
unorm_c ( linedr, udir, &mag );
if ( mag == 0. )
{
setmsg_c( "Line direction vector is the zero vector. " );
sigerr_c( "SPICE(ZEROVECTOR)" );
chkout_c( "npedln_c" );
return;
}
if ( ( a <= 0. )
|| ( b <= 0. )
|| ( c <= 0. ) )
{
setmsg_c ( "Semi-axis lengths: a = #, b = #, c = #." );
errdp_c ( "#", a );
errdp_c ( "#", b );
errdp_c ( "#", c );
sigerr_c ( "SPICE(INVALIDAXISLENGTH)" );
chkout_c ( "npedln_c" );
return;
}
/*
Scale the semi-axes lengths for better numerical behavior.
If squaring any one of the scaled lengths causes it to
underflow to zero, we cannot continue the computation. Otherwise,
scale the viewing point too.
*/
scale = maxd_c ( 3, a, b, c );
scla = a / scale;
sclb = b / scale;
sclc = c / scale;
scla2 = scla*scla;
sclb2 = sclb*sclb;
sclc2 = sclc*sclc;
if ( ( (SpiceDouble)touchd_(&scla2) == 0. )
|| ( (SpiceDouble)touchd_(&sclb2) == 0. )
|| ( (SpiceDouble)touchd_(&sclc2) == 0. ) )
{
setmsg_c ( "Semi-axis too small: a = #, b = #, c = #. " );
errdp_c ( "#", a );
errdp_c ( "#", b );
errdp_c ( "#", c );
sigerr_c ( "SPICE(DEGENERATECASE)" );
chkout_c ( "npedln_c" );
return;
}
/*
Scale linept.
*/
sclpt[0] = linept[0] / scale;
sclpt[1] = linept[1] / scale;
sclpt[2] = linept[2] / scale;
/*
Hand off the intersection case to surfpt_c. surfpt_c determines
whether rays intersect a body, so we treat the line as a pair
of rays.
*/
vminus_c ( udir, oppdir );
surfpt_c ( sclpt, udir, scla, sclb, sclc, pt[0], &(found[0]) );
surfpt_c ( sclpt, oppdir, scla, sclb, sclc, pt[1], &(found[1]) );
for ( i = 0; i < 2; i++ )
{
if ( found[i] )
{
*dist = 0.0;
vequ_c ( pt[i], pnear );
vscl_c ( scale, pnear, pnear );
chkout_c ( "npedln_c" );
return;
}
}
/*
Getting here means the line doesn't intersect the ellipsoid.
Find the candidate ellipse CAND. NORMAL is a normal vector to
the plane containing the candidate ellipse. Mathematically the
ellipse must exist, since it's the intersection of an ellipsoid
centered at the origin and a plane containing the origin. Only
numerical problems can prevent the intersection from being found.
*/
normal[0] = udir[0] / scla2;
normal[1] = udir[1] / sclb2;
normal[2] = udir[2] / sclc2;
nvc2pl_c ( normal, 0., &candpl );
inedpl_c ( scla, sclb, sclc, &candpl, &cand, &xfound );
if ( !xfound )
{
setmsg_c ( "Candidate ellipse could not be found." );
sigerr_c ( "SPICE(DEGENERATECASE)" );
chkout_c ( "npedln_c" );
return;
}
/*
Project the candidate ellipse onto a plane orthogonal to the
line. We'll call the plane prjpl and the projected ellipse prjel.
*/
nvc2pl_c ( udir, 0., &prjpl );
pjelpl_c ( &cand, &prjpl, &prjel );
/*
Find the point on the line lying in the projection plane, and
then find the near point PRJNPT on the projected ellipse. Here
PRJPT is the point on the line lying in the projection plane.
The distance between PRJPT and PRJNPT is DIST.
*/
vprjp_c ( sclpt, &prjpl, prjpt );
npelpt_c ( prjpt, &prjel, prjnpt, dist );
/*
Find the near point pnear on the ellipsoid by taking the inverse
orthogonal projection of prjnpt; this is the point on the
candidate ellipse that projects to prjnpt. Note that the
output dist was computed in step 3 and needs only to be re-scaled.
The inverse projection of pnear ought to exist, but may not
be calculable due to numerical problems (this can only happen
when the input ellipsoid is extremely flat or needle-shaped).
*/
vprjpi_c ( prjnpt, &prjpl, &candpl, pnear, &ifound );
if ( !ifound )
{
setmsg_c ( "Inverse projection could not be found." );
sigerr_c ( "SPICE(DEGENERATECASE)" );
chkout_c ( "npedln_c" );
return;
}
/*
Undo the scaling.
*/
vscl_c ( scale, pnear, pnear );
*dist *= scale;
chkout_c ( "npedln_c" );
} /* End npedln_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 errprt_c ( ConstSpiceChar * op,
SpiceInt lenout,
SpiceChar * list )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
op I The operation: "GET" or "SET".
lenout I Length of list for output.
list I/O Specification of error messages to be output.
-Detailed_Input
op indicates the operation to be performed. Possible
values are "GET" and "SET".
"SET" means, "the following list specifies the default
selection of error messages to be output." These are
the messages that will be output to the default error
output device (selected by errdev_c) when an error is
detected.
"GET" means, "return the current list of error output
items." This is the exact list that was set by the
last call to this routine with the "SET" option.
The option can be specified in mixed case. For example,
the following call will work:
errprt_c ( "SeT", lenout, "ALL" )
lenout is the allowed length of list when list is returning a
the error message list. The size described by lenout
should be large enough to hold any possible output plus 1.
list is a list of error message items. The items
are delimited by commas. The items that can be
in the list are the words:
1. SHORT ...indicates the short error message
2. EXPLAIN ...the explanation of the short message
3. LONG ...the long error message
4. TRACEBACK ...the traceback
5. ALL ...indicates "output all messages"
6. NONE ...indicates "don't output any messages"
7. DEFAULT ...same as ALL, but includes default
message
A "list" is a character string containing some or
all of the above words, delimited by commas. Examples
are:
1. "SHORT, EXPLAIN"
2. "SHORT, LONG"
3. "ALL"
4. "NONE"
5. "ALL, NONE, ALL, SHORT, NONE"
Each word in the list can be thought of as
"flipping a switch" to enable or disable the output
of the message(s) indicated by the word. The
words are acted on in the order they occur in the
list, starting with the leftmost word. As examples,
consider the sample lists above.
The effect of the first list above, "SHORT, EXPLAIN",
is to enable the output of the short error message
and the explanatory text corresponding to it.
The effect of the second list is to enable the output
of the short and long messages.
The effect of the third list is to enable the output of
all of the error messages (short, long, explanation
of the short message, and traceback).
The effect of the fourth list is to disable output of
all of the messages.
The effect of the fifth list is to disable output of
all of the messages. The reason for this is that
the words in the list are responded to in order,
from left to right, and "NONE" is the last word.
If any words other than SHORT, LONG, EXPLAIN, ALL,
DEFAULT, TRACEBACK or NONE appear in list, those words
that are recognized are responded to. The words
that are not recognized are diagnosed as
erroneous, and error messages are generated
for each such unrecognized word.
The length of list is caller-defined, but only
the first 100 characters of list will be saved
for later retrieval.
Only the first 10 items in the list are used;
the rest are ignored.
-Detailed_Output
list is a list of error message items. The value of
list is that set by the last call to this routine
using the "SET" option. See "Detailed Input"
for a description of the possible values and
meanings of list.
The initial value returned is "DEFAULT".
Only the first 100 characters of list are saved
when the list is set; any additional characters
are truncated. Therefore, the first 100
characters, at most, of the saved value of list
will be returned.
-Parameters
None.
-Exceptions
1) If the input argument op does not indicate a valid operation,
the error SPICE(INVALIDOPERATION) will be signaled.
2) If the input argument list does not indicate a valid list of
error message types, the error SPICE(INVALIDLISTITEM) will be
signaled.
3) 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.
4) The error SPICE(NULLPOINTER) is signalled if the input string
pointer is null.
5) The user must pass a value indicating the length of the output
string, when list is an output. If this value is not at least 2,
the error SPICE(STRINGTOOSHORT) is signaled.
Also, this routine is part of the CSPICE error
handling mechanism.
-Files
None.
-Particulars
Please read the "required reading"!
This routine is intended to be used in conjunction with
errdev_c, which selects the default output device to which
the error messages selected by this routine will be
output.
Additionally, the error response action must be
something other than "IGNORE" if the error messages
are to be output. Possible choices of the error
response action are "RETURN", "REPORT", "ABORT", "DEFAULT", and
"IGNORE". Use erract_c to set the error response action.
Only the first 100 characters of list are saved.
The default set of error messages that are output is the
set specified by "DEFAULT"; i.e., all of them, including
the "default" message.
-Examples
1. In this example, we select as the output device
the file, SPUD.DAT, and then select the error
messages to be output. We choose the short
error message and the traceback. Since a
different set of messages may have been selected
previously, we clear the old setting by putting
the word, "NONE", at the beginning of the list.
/.
Set the error output device to SPUD.DAT:
./
errdev_c ( "SET", lenout, "SPUD.DAT" );
/.
Choose error messages:
./
errprt_c ( "SET", lenout, "NONE, SHORT, TRACEBACK" );
2. In this example we are retrieving the error message list.
/.
Declare the output string and its size.
./
#define LENOUT 50
SpiceChar list[ LENOUT ];
errdev_c ( "GET", LENOUT, list );
-Restrictions
The device to which the selected error messages will
be written must be selected via errdev_c; otherwise,
messages will be written to the initial default device.
Only the first 100 characters of list are saved.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
-Version
-CSPICE Version 1.3.0, 24-JUN-2003 (NJB)
Bug fix: case of invalid operation keyword is now
diagnosed, as per the Exceptions section of the header.
-CSPICE Version 2.0.0, 09-FEB-1998 (NJB) (EDW)
Input argument op was changed to type ConstSpiceChar *.
Re-implemented routine without dynamically allocated, temporary
strings.
Corrected errors in examples in which the call sequence
was incorrect.
-CSPICE Version 1.0.0, 25-OCT-1997 (EDW)
-Index_Entries
get/set error output items
-&
*/
{ /* Begin errprt_c */
/*
Participate in error tracing.
*/
if ( return_c() )
{
return;
}
chkin_c ( "errprt_c" );
/*
Check the input string op to make sure the pointer is non-null
and the string length is non-zero.
*/
CHKFSTR ( CHK_STANDARD, "errprt_c", op );
if ( eqstr_c ( op, "SET") )
{
/*
Operation is SET. The argument "list" will be an input string.
Check "list" as well.
*/
CHKFSTR ( CHK_STANDARD, "errprt_c", list );
errprt_( ( char * ) op,
( char * ) list,
( ftnlen ) strlen(op),
( ftnlen ) strlen(list) );
}
else if ( eqstr_c (op, "GET" ) )
{
/*
Operation is GET. "list" will be an output string.
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, "errprt_c", list, lenout );
/*
After the routine call, create a C string from the
Fortran output string.
*/
errprt_( ( char * ) op,
( char * ) list,
( ftnlen ) strlen(op),
( ftnlen ) lenout-1 );
F2C_ConvertStr( lenout, list );
}
else
{
setmsg_c ( "Input argument op had value: # "
"Valid choices are GET or SET." );
errch_c ( "#", op );
sigerr_c ( "SPICE(INVALIDOPERATION)" );
chkout_c ( "errprt_c" );
return;
}
chkout_c ( "errprt_c" );
} /* End errprt_c */
void qcktrc_c ( SpiceInt tracelen,
SpiceChar * trace )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
tracelen I Maximum length of output traceback string.
trace O A traceback string.
SPICE_ERROR_MAXMOD
P Maximum traceback module count.
SPICE_ERROR_MODLEN
P Maximum module name length.
SPICE_ERROR_TRCLEN
P Maximum length of output traceback string.
-Detailed_Input
None.
-Detailed_Output
trace is a list of module names, delimited by the string,
" --> ". An example would be
"SPUD --> SPAM --> FOOBAR".
The maximum length of the returned string is given
by the parameter SPICE_ERROR_TRCLEN. The value of this
parameter includes room for the terminating null.
In general, the meaning of the trace is as follows:
The first name in the list is the name of the first
module to check in (that hasn't yet checked out). The
last name is the name of the module at the end of the
call chain; this is the last module that checked in.
The meaning of the traceback depends on the state
of the error handling mechanism. There are two
cases:
1) In RETURN mode, when an error is signaled, the
traceback at that point is saved. trcdep_c,
trcnam_c, and qcktrc_c return values
pertaining to the saved traceback.
2) In all other modes, the traceback represents
the CURRENT call chain. trcdep_c, trcnam_c,
and qcktrc_c return values pertaining to the
current trace representation.
Any module names exceeding SPICE_ERROR_MODLEN
characters in length are truncated on the right.
-Parameters
The following parameters are declared in the header file SpiceErr.h:
SPICE_ERROR_MAXMOD is the maximum number of module names that can
be accommodated in the SPICE trace stack; this
is the maximum number of names that can appear
in the output traceback.
SPICE_ERROR_MODLEN is the maximum module name length that can be
accommodated by this routine.
SPICE_ERROR_TRCLEN is the maximum length of the string returned
by this routine. The value of this parameter
includes room for the terminating null.
-Exceptions
1) If the output string pointer is null, the error SPICE(NULLPOINTER)
will be signaled.
2) If the output string has length less than 2 characters, the error
SPICE(STRINGTOOSHORT) will be signaled.
-Files
None.
-Particulars
This routine is part of the CSPICE error handling mechanism.
-Examples
1) Deliberately generate a SPICE error to demonstrate use of
this routine together with trcnam_c. We'll attempt to look up
a state vector via spkezr_c without first having loaded any
SPK files.
Example code begins here.
#include <stdio.h>
#include "SpiceUsr.h"
int main()
{
/.
Local constants
./
#define ACTION "RETURN"
/.
Local variables
./
SpiceChar * abcorr;
SpiceChar trace [ SPICE_ERROR_TRCLEN ];
SpiceChar * obsrvr;
SpiceChar * frame;
SpiceChar * target;
SpiceDouble et;
SpiceDouble lt;
SpiceDouble state [6];
/.
Set error handling action to RETURN so that this program
won't terminate when a SPICE error is signaled. Note that
the input string length argument is unused for a "SET"
operation.
./
erract_c ( "SET", 0, ACTION );
/.
Generate a SPICE error: call spkezr_c without first having
loaded an SPK file.
./
et = 0.0;
target = "Moon";
obsrvr = "Earth";
frame = "J2000";
abcorr = "NONE";
spkezr_c ( target, et, frame, abcorr, obsrvr, state, < );
if ( failed_c() )
{
/.
An error has been signaled. Fetch and display
the traceback.
./
qcktrc_c ( SPICE_ERROR_TRCLEN, trace );
printf ( "Traceback: \n%s\n", trace );
/.
Reset the error status so that CSPICE can resume normal
operation.
./
reset_c();
}
return ( 0 );
}
When this program was executed on a PC/Linux/gcc platform, the
output (which has been reformatted to fit in the available
space in this header) was:
====================================================================
============
Toolkit version: N0065
SPICE(NOLOADEDFILES) --
At least one SPK file needs to be loaded by SPKLEF before beginning
a search.
A traceback follows. The name of the highest level module is first.
spkezr_c --> SPKEZR --> SPKEZ --> SPKGEO --> SPKSFS
====================================================================
============
Traceback:
spkezr_c --> SPKEZR --> SPKEZ --> SPKGEO --> SPKSFS
-Restrictions
1) It is assumed no module names exceed SPICE_ERROR_MODLEN
characters in length.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
K.R. Gehringer (JPL)
-Version
-CSPICE Version 1.0.0, 05-NOV-2013 (NJB) (KRG)
-Index_Entries
get quick traceback
-&
*/
{ /* Begin qcktrc_c */
/*
This routine does not check in unless an input error occurs.
*/
/*
Make sure the output string has at least enough room for one output
character and a null terminator. Also check for a null pointer.
We don't use the usual CHKOSTR macro here because we must reset
the error status before signaling an error.
*/
if ( trace == NULL )
{
reset_c ();
chkin_c ( "qcktrc_c" );
setmsg_c ( "The output string pointer 'trace' is null." );
sigerr_c ( "SPICE(NULLPOINTER)" );
chkout_c ( "qcktrc_c" );
return;
}
if ( tracelen < 2 )
{
reset_c ();
chkin_c ( "qcktrc_c" );
setmsg_c ( "The output string 'trace' has length #; the "
"minimum allowed length is 2 characters." );
errint_c ( "#", tracelen );
sigerr_c ( "SPICE(STRINGTOOSHORT)" );
chkout_c ( "qcktrc_c" );
return;
}
/*
Fetch the traceback.
*/
qcktrc_ ( ( char * ) trace,
( ftnlen ) tracelen-1 );
/*
Convert the output name string to a null-terminated,
C style string.
*/
F2C_ConvertStr ( tracelen, trace );
} /* End qcktrc_c */
void gfposc_c ( ConstSpiceChar * target,
ConstSpiceChar * frame,
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
frame I Name of the reference frame for coordinate calculations
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.
frame the string name of the reference frame in which to perform
state look-ups and coordinate calculations.
The SPICE frame subsystem must recognize the 'frame' name.
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:
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'
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
observer-target 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 observer-target
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, gfposc_c finds times when the
observer-target 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 observer-target vector coordinate has
values between ABSMAX - adjust and ABSMAX.
For relate set to ABSMIN, the result window contains
time intervals when the observer-target 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 observer-target 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 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 gfposc_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
observer-target 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 observer-target 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 examples shown below require 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
naif0009.tls Leapseconds kernel
earthstns_itrf93_050714.bsp SPK for DSN Station Locations
earth_topo_050714.tf Topocentric DSN stations frame
definitions
earth_000101_080120_071029.bpc High precision earth PCK
\begindata
KERNELS_TO_LOAD = (
'/kernels/gen/lsk/naif0008.tls'
'/kernels/gen/spk/de414.bsp'
'/kernels/gen/pck/pck00008.tpc'
'/kernels/gen/spk/earthstns_itrf93_050714.bsp',
'/kernels/gen/fk/earth_topo_050714.tf',
'/kernels/gen/pck/earth_000101_080120_071029.bpc',
)
Example(1):
Find the time during 2007 for which the latitude of the
Earth-Sun vector in IAU_EARTH frame has the maximum value,
i.e. the latitude of the Tropic of Cancer.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "SpiceUsr.h"
#define MAXWIN 750
#define TIMFMT "YYYY-MON-DD HR:MN:SC.###### (TDB) ::TDB ::RND"
#define TIMLEN 41
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 * relate = "ABSMAX";
SpiceChar * crdsys = "LATITUDINAL";
SpiceChar * coord = "LATITUDE";
SpiceChar * targ = "SUN";
SpiceChar * obsrvr = "EARTH";
SpiceChar * frame = "IAU_EARTH";
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 );
/.
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.;
refval = 0;
/.
List the beginning and ending points in each interval
if result contains data.
./
gfposc_c ( targ,
frame,
abcorr,
obsrvr,
crdsys,
coord,
relate,
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 );
if ( beg == end )
{
timout_c ( beg, TIMFMT, TIMLEN, begstr );
printf ( "Event time: %s\n", begstr );
}
else
{
timout_c ( beg, TIMFMT, TIMLEN, begstr );
timout_c ( end, TIMFMT, TIMLEN, endstr );
printf ( "Interval %d\n", i + 1);
printf ( "From : %s \n", begstr );
printf ( "To : %s \n", endstr );
printf( " \n" );
}
}
}
kclear_c();
return( 0 );
}
The program outputs:
Event time: 2007-JUN-21 17:54:13.166910 (TDB)
Example(2):
A minor modification of the program listed in Example 1; find the
time during 2007 for which the latitude of the Earth-Sun vector
in IAU_EARTH frame has the minimum value, i.e. the latitude of
the Tropic of Capricorn.
Edit the example program, assign:
SpiceChar * relate = "ABSMIN";
The program outputs:
Event time: 2007-DEC-22 06:04:32.630160 (TDB)
Example(3):
Find the time during 2007 for which the Z component of the
Earth-Sun vector in IAU_EARTH frame has value 0, i.e. crosses
the equatorial plane (this also defines a zero latitude).
The search should return two times, one for an ascending
passage and one for descending.
Edit the example program, assign:
SpiceChar * relate = "=";
SpiceChar * crdsys = "RECTANGULAR";
SpiceChar * coord = "Z";
Note, this RELATE operator refers to the REFVAL value,
assigned to 0.D0 for this example.
The program outputs:
Event time: 2007-MAR-21 00:01:25.495120 (TDB)
Event time: 2007-SEP-23 09:46:39.574124 (TDB)
Example(4):
Find the times between Jan 1, 2007 and Jan 1, 2008 corresponding
to the apoapsis on the Moon's orbit around the Earth (note, the
GFDIST routine can also perform this search).
Edit the example program, assign:
This search requires a change in the step size since the Moon's
orbit about the earth (earth-moon barycenter) has a twenty-eight
day period. Use a step size something less than half that value.
In this case, we use twelve days.
SpiceChar * relate = "LOCMAX";
SpiceChar * crdsys = "SPHERICAL";
SpiceChar * coord = "RADIUS";
SpiceChar * targ = "MOON";
SpiceChar * frame = "J2000";
step = 12.*spd_c();
The program outputs:
Event time: 2007-JAN-10 16:26:18.805837 (TDB)
Event time: 2007-FEB-07 12:39:35.078525 (TDB)
Event time: 2007-MAR-07 03:38:07.334769 (TDB)
Event time: 2007-APR-03 08:38:55.222606 (TDB)
Event time: 2007-APR-30 10:56:49.847027 (TDB)
Event time: 2007-MAY-27 22:03:28.857783 (TDB)
Event time: 2007-JUN-24 14:26:23.639351 (TDB)
Event time: 2007-JUL-22 08:43:50.135565 (TDB)
Event time: 2007-AUG-19 03:28:33.538169 (TDB)
Event time: 2007-SEP-15 21:07:13.964698 (TDB)
Event time: 2007-OCT-13 09:52:30.819372 (TDB)
Event time: 2007-NOV-09 12:32:50.070555 (TDB)
Event time: 2007-DEC-06 16:54:31.225504 (TDB)
Example(5):
Find times between Jan 1, 2007 and Jan 1, 2008 when the latitude
(elevation) of the observer-target vector between DSS 17 and the
Moon, as observed in the DSS 17 topocentric (station) frame,
exceeds 83 degrees.
Edit the example program, assign:
This search uses a step size of four hours since the time
for all declination zero-to-max-to-zero passes within
the search window exceeds eight hours.
SpiceChar * relate = ">";
SpiceChar * crdsys = "LATITUDINAL";
SpiceChar * coord = "LATITUDE";
SpiceChar * targ = "MOON";
SpiceChar * obsrvr = "DSS-17";
SpiceChar * frame = "DSS-17_TOPO";
step = (4./24.)*spd_c();
refval = 83. * rpd_c();
The program outputs:
Interval 1
From : 2007-FEB-26 03:18:48.229806 (TDB)
To : 2007-FEB-26 03:31:29.734169 (TDB)
Interval 2
From : 2007-MAR-25 01:12:38.551183 (TDB)
To : 2007-MAR-25 01:23:53.908601 (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)
Correction of several typos.
-CSPICE Version 1.0.0, 10-FEB-2009 (NJB) (EDW)
-Index_Entries
GF position coordinate search
-&
*/
{ /* Begin gfposc_c */
/*
Local variables
*/
doublereal * work;
SpiceInt nBytes;
static SpiceInt nw = SPICE_GF_NWMAX;
/*
Participate in error tracing.
*/
if ( return_c() )
{
return;
}
chkin_c ( "gfposc_c" );
/*
Make sure cell data types are d.p.
*/
CELLTYPECHK2 ( CHK_STANDARD, "gfposc_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, "gfposc_c", target );
CHKFSTR ( CHK_STANDARD, "gfposc_c", frame );
CHKFSTR ( CHK_STANDARD, "gfposc_c", abcorr );
CHKFSTR ( CHK_STANDARD, "gfposc_c", obsrvr );
CHKFSTR ( CHK_STANDARD, "gfposc_c", crdsys );
CHKFSTR ( CHK_STANDARD, "gfposc_c", coord );
CHKFSTR ( CHK_STANDARD, "gfposc_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 ( "gfposc_c" );
return;
}
/*
Let the f2'd routine do the work.
*/
gfposc_( ( char * ) target,
( char * ) frame,
( 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(frame),
( 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 ( "gfposc_c" );
} /* End gfposc_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 npelpt_c ( ConstSpiceDouble point [3],
ConstSpiceEllipse * ellips,
SpiceDouble pnear [3],
SpiceDouble * dist )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
point I Point whose distance to an ellipse is to be found.
ellips I A CSPICE ellipse.
pnear O Nearest point on ellipse to input point.
dist O Distance of input point to ellipse.
-Detailed_Input
ellips is a CSPICE ellipse that represents an ellipse
in three-dimensional space.
point is a point in 3-dimensional space.
-Detailed_Output
pnear is the nearest point on ellips to point.
dist is the distance between point and pnear. This is
the distance between point and the ellipse.
-Parameters
None.
-Exceptions
1) Invalid ellipses will be diagnosed by routines called by
this routine.
2) Ellipses having one or both semi-axis lengths equal to zero
are turned away at the door; the error SPICE(DEGENERATECASE)
is signalled.
3) If the geometric ellipse represented by ellips does not
have a unique point nearest to the input point, any point
at which the minimum distance is attained may be returned
in pnear.
-Files
None.
-Particulars
Given an ellipse and a point in 3-dimensional space, if the
orthogonal projection of the point onto the plane of the ellipse
is on or outside of the ellipse, then there is a unique point on
the ellipse closest to the original point. This routine finds
that nearest point on the ellipse. If the projection falls inside
the ellipse, there may be multiple points on the ellipse that are
at the minimum distance from the original point. In this case,
one such closest point will be returned.
This routine returns a distance, rather than an altitude, in
contrast to the CSPICE routine nearpt_c. Because our ellipse is
situated in 3-space and not 2-space, the input point is not
`inside' or `outside' the ellipse, so the notion of altitude does
not apply to the problem solved by this routine. In the case of
nearpt_c, the input point is on, inside, or outside the ellipsoid,
so it makes sense to speak of its altitude.
-Examples
1) For planetary rings that can be modelled as flat disks with
elliptical outer boundaries, the distance of a point in
space from a ring's outer boundary can be computed using this
routine. Suppose center, smajor, and sminor are the center,
semi-major axis, and semi-minor axis of the ring's boundary.
Suppose also that scpos is the position of a spacecraft.
scpos, center, smajor, and sminor must all be expressed in
the same coordinate system. We can find the distance from
the spacecraft to the ring using the code fragment
#include "SpiceUsr.h"
.
.
.
/.
Make a CSPICE ellipse representing the ring,
then use npelpt_c to find the distance between
the spacecraft position and RING.
./
cgv2el_c ( center, smajor, sminor, ring );
npelpt_c ( scpos, ring, pnear, &dist );
2) The problem of finding the distance of a line from a tri-axial
ellipsoid can be reduced to the problem of finding the
distance between the same line and an ellipse; this problem in
turn can be reduced to the problem of finding the distance
between an ellipse and a point. The routine npedln_c carries
out this process and uses npelpt_c to find the ellipse-to-point
distance.
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
-Version
-CSPICE Version 1.0.0, 02-SEP-1999 (NJB)
-Index_Entries
nearest point on ellipse to point
-&
*/
{ /* Begin npelpt_c */
/*
Local variables
*/
SpiceDouble center [3];
SpiceDouble majlen;
SpiceDouble minlen;
SpiceDouble rotate [3][3];
SpiceDouble scale;
SpiceDouble smajor [3];
SpiceDouble sminor [3];
SpiceDouble tmppnt [3];
SpiceDouble prjpnt [3];
/*
Participate in error tracing.
*/
chkin_c ( "npelpt_c" );
/*
Here's an overview of our solution:
Let ELPL be the plane containing the ELLIPS, and let PRJ be
the orthogonal projection of the POINT onto ELPL. Let X be
any point in the plane ELPL. According to the Pythagorean
Theorem,
2 2 2
|| POINT - X || = || POINT - PRJ || + || PRJ - X ||.
Then if we can find a point X on ELLIPS that minimizes the
rightmost term, that point X is the closest point on the
ellipse to POINT.
So, we find the projection PRJ, and then solve the problem of
finding the closest point on ELLIPS to PRJ. To solve this
problem, we find a triaxial ellipsoid whose intersection with
the plane ELPL is precisely ELLIPS, and two of whose axes lie
in the plane ELPL. The closest point on ELLIPS to PRJ is also
the closest point on the ellipsoid to ELLIPS. But we have the
SPICELIB routine NEARPT on hand to find the closest point on an
ellipsoid to a specified point, so we've reduced our problem to
a solved problem.
There is a subtle point to worry about here: if PRJ is outside
of ELLIPS (PRJ is in the same plane as ELLIPS, so `outside'
does make sense here), then the closest point on ELLIPS to PRJ
coincides with the closest point on the ellipsoid to PRJ,
regardless of how we choose the z-semi-axis length of the
ellipsoid. But the correspondence may be lost if PRJ is inside
the ellipse, if we don't choose the z-semi-axis length
correctly.
Though it takes some thought to verify this (and we won't prove
it here), making the z-semi-axis of the ellipsoid longer than
the other two semi-axes is sufficient to maintain the
coincidence of the closest point on the ellipsoid to PRJPNT and
the closest point on the ellipse to PRJPNT.
*/
/*
Find the ellipse's center and semi-axes.
*/
el2cgv_c ( ellips, center, smajor, sminor );
/*
Find the lengths of the semi-axes, and scale the vectors to try
to prevent arithmetic unpleasantness. Degenerate ellipses are
turned away at the door.
*/
minlen = vnorm_c (sminor);
majlen = vnorm_c (smajor);
if ( MinVal ( majlen, minlen ) == 0.0 )
{
setmsg_c ( "Ellipse semi-axis lengths: # #." );
errdp_c ( "#", majlen );
errdp_c ( "#", minlen );
sigerr_c ( "SPICE(DEGENERATECASE)" );
chkout_c ( "npelpt_c" );
return;
}
scale = 1.0 / majlen;
vscl_c ( scale, smajor, smajor );
vscl_c ( scale, sminor, sminor );
/*
Translate ellipse and point so that the ellipse is centered at
the origin. Scale the point's coordinates to maintain the
correct relative position to the scaled ellipse.
*/
vsub_c ( point, center, tmppnt );
vscl_c ( scale, tmppnt, tmppnt );
/*
We want to reduce the problem to a two-dimensional one. We'll
work in a coordinate system whose x- and y- axes are aligned with
the semi-major and semi-minor axes of the input ellipse. The
z-axis is picked to give us a right-handed system. We find the
matrix that transforms coordinates to our new system using twovec_c.
*/
twovec_c ( smajor, 1, sminor, 2, rotate );
/*
Apply the coordinate transformation to our scaled input point.
*/
mxv_c ( rotate, tmppnt, tmppnt );
/*
We must find the distance between the orthogonal projection of
tmppnt onto the x-y plane and the ellipse. The projection is
just
( TMPPNT[0], TMPPNT[1], 0 );
we'll call this projection prjpnt.
*/
vpack_c ( tmppnt[0], tmppnt[1], 0.0, prjpnt );
/*
Now we're ready to find the distance between and a triaxial
ellipsoid whose intersection with the x-y plane is the ellipse
and whose third semi-axis lies on the z-axis.
Because we've scaled the ellipse's axes so as to give the longer
axis length 1, a length of 2.0 suffices for the ellipsoid's
z-semi-axis.
Find the nearest point to prjpnt on the ellipoid, pnear.
*/
nearpt_c ( prjpnt, 1.0, minlen/majlen, 2.0, pnear, dist );
/*
Scale the near point coordinates back to the original scale.
*/
vscl_c ( majlen, pnear, pnear );
/*
Apply the required inverse rotation and translation to pnear.
Compute the point-to-ellipse distance.
*/
mtxv_c ( rotate, pnear, pnear );
vadd_c ( pnear, center, pnear );
*dist = vdist_c ( pnear, point );
chkout_c ( "npelpt_c" );
} /* End npelpt_c */
void nplnpt_c ( ConstSpiceDouble linpt [3],
ConstSpiceDouble lindir [3],
ConstSpiceDouble point [3],
SpiceDouble pnear [3],
SpiceDouble * dist )
/*
-Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
linpt,
lindir I Point on a line and the line's direction vector.
point I A second point.
pnear O Nearest point on the line to point.
dist O Distance between point and pnear.
-Detailed_Input
linpt
lindir are, respectively, a point and a direction vector
that define a line in 3-dimensional space. The
line is the set of points
linpt + t * lindir
where t is any real number.
point is a point in 3-dimensional space.
-Detailed_Output
pnear is the nearest point on the input line to the input
point.
dist is the distance between the input line and input
point.
-Parameters
None.
-Exceptions
1) If the line direction vector lindir is the zero vector, the
error SPICE(ZEROVECTOR) is signaled.
-Files
None.
-Particulars
For every line L and point P, there is a unique closest point
on L to P. Call this closest point C. It is always true that
P - C is perpendicular to L, and the length of P - C is called
the "distance" between P and L.
-Examples
1) Suppose a line passes through the point ( 1, 2, 3 ) and
has direction vector ( 0, 1, 1 ). We wish to find the
closest point on the line to the point ( -6, 9, 10 ). We
can use the code fragment
#include "SpiceUsr.h"
.
.
.
LINPT[0] = 1.0;
LINPT[1] = 2.0;
LINPT[2] = 3.0;
LINDIR[0] = 0.0;
LINDIR[1] = 1.0;
LINDIR[2] = 1.0;
POINT[0] = -6.0;
POINT[1] = 9.0;
POINT[2] = 10.0;
nplnpt_c ( linpt, lindir, point, pnear, &dist );
After the call, pnear will take the value
( 1., 9., 10. );
dist will be 7.0.
-Restrictions
None.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
-Version
-CSPICE Version 1.0.0, 16-AUG-1999 (NJB)
-Index_Entries
distance between point and line
nearest point on line to point
-&
*/
{ /* Begin nplnpt_c */
/*
Local variables
*/
SpiceDouble trans [3];
/*
We need a real direction vector to work with.
*/
if ( vzero_c (lindir) )
{
chkin_c ( "nplnpt_c" );
setmsg_c ( "Direction vector must be non-zero." );
sigerr_c ( "SPICE(ZEROVECTOR)" );
chkout_c ( "nplnpt_c" );
return;
}
/*
We translate line and input point so as to put the line through
the origin. Then the nearest point on the translated line to the
translated point TRANS is the projection of TRANS onto the line.
*/
vsub_c ( point, linpt, trans );
vproj_c ( trans, lindir, pnear );
vadd_c ( pnear, linpt, pnear );
*dist = vdist_c ( pnear, point );
} /* End nplnpt_c */
void union_c ( SpiceCell * a,
SpiceCell * b,
SpiceCell * c )
/*
-Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
a I First input set.
b I Second input set.
c O Union of a and b.
-Detailed_Input
a is a CSPICE set. a must be declared as a SpiceCell
of data type character, double precision, or integer.
b is a CSPICE set, distinct from a. b must have the
same data type as a.
-Detailed_Output
c is a CSPICE set, distinct from sets a and b, which
contains the union of a and b (that is, all of
the elements which are in a or b or both). c must
have the same data type as a and b.
When comparing elements of character sets, this routine
ignores trailing blanks. Trailing blanks will be
trimmed from the members of the output set c.
-Parameters
None.
-Exceptions
1) If the input set arguments don't have identical data types,
the error SPICE(TYPEMISMATCH) is signaled.
2) If the union of the two sets contains more elements than can be
contained in the output set, the error SPICE(SETEXCESS) is signaled.
3) If the set arguments have character type and the length of the
elements of the output set is less than the maximum of the
lengths of the elements of the input sets, the error
SPICE(ELEMENTSTOOSHORT) is signaled.
4) If either of the input arguments may be unordered or contain
duplicates, the error SPICE(NOTASET) is signaled.
-Files
None.
-Particulars
This is a generic CSPICE set routine; it operates on sets of any
supported data type.
The union of two sets contains every element which is
in the first set, or in the second set, or in both sets.
{a,b} union {c,d} = {a,b,c,d}
{a,b,c} {b,c,d} {a,b,c,d}
{a,b,c,d} {} {a,b,c,d}
{} {a,b,c,d} {a,b,c,d}
{} {} {}
-Examples
1) The following code fragment places the union of the character sets
planets and asteroids into the character set result.
#include "SpiceUsr.h"
.
.
.
/.
Declare the sets with string length NAMLEN and with maximum
number of elements MAXSIZ.
./
SPICECHAR_CELL ( planets, MAXSIZ, NAMLEN );
SPICECHAR_CELL ( asteroids, MAXSIZ, NAMLEN );
SPICECHAR_CELL ( result, MAXSIZ, NAMLEN );
.
.
.
/.
Compute the union.
./
union_c ( &planets, &asteroids, &result );
2) Repeat example #1, this time using integer sets containing
ID codes of the bodies of interest.
#include "SpiceUsr.h"
.
.
.
/.
Declare the sets with maximum number of elements MAXSIZ.
./
SPICEINT_CELL ( planets, MAXSIZ );
SPICEINT_CELL ( asteroids, MAXSIZ );
SPICEINT_CELL ( result, MAXSIZ );
.
.
.
/.
Compute the union.
./
union_c ( &planets, &asteroids, &result );
3) Construct a set containing the periapse and apoapse TDB epochs
of an orbiter, given two separate sets containing the epochs of
those events.
#include "SpiceUsr.h"
.
.
.
/.
Declare the sets with maximum number of elements MAXSIZ.
./
SPICEDOUBLE_CELL ( periapse, MAXSIZ );
SPICEDOUBLE_CELL ( apoapse, MAXSIZ );
SPICEDOUBLE_CELL ( result, MAXSIZ );
.
.
.
/.
Compute the union.
./
union_c ( &periapse, &apoapse, &result );
-Restrictions
1) The output set must be distinct from both of the input sets.
For example, the following calls are invalid.
union_c ( ¤t, &new, ¤t );
union_c ( &new, ¤t, ¤t );
In each of the examples above, whether or not the subroutine
signals an error, the results will almost certainly be wrong.
Nearly the same effect can be achieved, however, by placing the
result into a temporary set, which is immediately copied back
into one of the input sets, as shown below.
union_c ( ¤t, &new, &temp );
copy_c ( &temp, &new );
2) String comparisons performed by this routine are Fortran-style:
trailing blanks in the input sets are ignored. This gives
consistent behavior with CSPICE code generated by the f2c
translator, as well as with the Fortran SPICE Toolkit.
Note that this behavior is not identical to that of the ANSI
C library functions strcmp and strncmp.
-Literature_References
None.
-Author_and_Institution
N.J. Bachman (JPL)
C.A. Curzon (JPL)
W.L. Taber (JPL)
I.M. Underwood (JPL)
-Version
-CSPICE Version 1.1.0, 15-FEB-2005 (NJB)
Bug fix: loop bound changed from 2 to 3 in loop used
to free dynamically allocated arrays.
-CSPICE Version 1.0.0, 08-AUG-2002 (NJB) (CAC) (WLT) (IMU)
-Index_Entries
union of two sets
-&
*/
{ /* Begin union_c */
/*
Local variables
*/
SpiceChar * fCell[3];
SpiceInt fLen [3];
SpiceInt i;
/*
Standard SPICE error handling.
*/
if ( return_c() )
{
return;
}
chkin_c ( "union_c" );
/*
Make sure data types match.
*/
CELLMATCH3 ( CHK_STANDARD, "union_c", a, b, c );
/*
Make sure the input cells are sets.
*/
CELLISSETCHK2 ( CHK_STANDARD, "union_c", a, b );
/*
Initialize the cells if necessary.
*/
CELLINIT3 ( a, b, c );
/*
Call the union routine appropriate for the data type of the cells.
*/
if ( a->dtype == SPICE_CHR )
{
/*
Construct Fortran-style sets suitable for passing to unionc_.
*/
C2F_MAP_CELL3 ( "",
a, fCell, fLen,
b, fCell+1, fLen+1,
c, fCell+2, fLen+2 );
if ( failed_c() )
{
chkout_c ( "union_c" );
return;
}
unionc_ ( (char * ) fCell[0],
(char * ) fCell[1],
(char * ) fCell[2],
(ftnlen ) fLen[0],
(ftnlen ) fLen[1],
(ftnlen ) fLen[2] );
/*
Map the union back to a C style cell.
*/
F2C_MAP_CELL ( fCell[2], fLen[2], c );
/*
We're done with the dynamically allocated Fortran-style arrays.
*/
for ( i = 0; i < 3; i++ )
{
free ( fCell[i] );
}
}
else if ( a->dtype == SPICE_DP )
{
uniond_ ( (doublereal * ) (a->base),
(doublereal * ) (b->base),
(doublereal * ) (c->base) );
/*
Sync the output cell.
*/
if ( !failed_c() )
{
zzsynccl_c ( F2C, c );
}
}
else if ( a->dtype == SPICE_INT )
{
unioni_ ( (integer * ) (a->base),
(integer * ) (b->base),
(integer * ) (c->base) );
/*
Sync the output cell.
*/
if ( !failed_c() )
{
zzsynccl_c ( F2C, c );
}
}
else
{
setmsg_c ( "Cell a contains unrecognized data type code #." );
errint_c ( "#", (SpiceInt) (a->dtype) );
sigerr_c ( "SPICE(NOTSUPPORTED)" );
chkout_c ( "union_c" );
return;
}
/*
Indicate the result is a set.
*/
c->isSet = SPICETRUE;
chkout_c ( "union_c" );
} /* End union_c */
