/* $Procedure LTIME ( Light Time ) */
/* Subroutine */ int ltime_(doublereal *etobs, integer *obs, char *dir,
integer *targ, doublereal *ettarg, doublereal *elapsd, ftnlen dir_len)
{
/* Builtin functions */
integer s_cmp(char *, char *, ftnlen, ftnlen);
/* Local variables */
doublereal sobs[6], myet, c__;
integer r__;
extern /* Subroutine */ int chkin_(char *, ftnlen), errch_(char *, char *,
ftnlen, ftnlen);
doublereal starg[6];
extern doublereal vdist_(doublereal *, doublereal *);
extern integer rtrim_(char *, ftnlen);
extern logical failed_(void);
doublereal lt;
extern doublereal clight_(void);
integer bcentr;
extern /* Subroutine */ int spkgeo_(integer *, doublereal *, char *,
integer *, doublereal *, doublereal *, ftnlen), sigerr_(char *,
ftnlen), chkout_(char *, ftnlen), setmsg_(char *, ftnlen);
extern logical return_(void);
/* $ Abstract */
/* This routine computes the transmit (or receive) time */
/* of a signal at a specified target, given the receive */
/* (or transmit) time at a specified observer. The elapsed */
/* time between transmit and receive is also returned. */
/* $ Disclaimer */
/* THIS SOFTWARE AND ANY RELATED MATERIALS WERE CREATED BY THE */
/* CALIFORNIA INSTITUTE OF TECHNOLOGY (CALTECH) UNDER A U.S. */
/* GOVERNMENT CONTRACT WITH THE NATIONAL AERONAUTICS AND SPACE */
/* ADMINISTRATION (NASA). THE SOFTWARE IS TECHNOLOGY AND SOFTWARE */
/* PUBLICLY AVAILABLE UNDER U.S. EXPORT LAWS AND IS PROVIDED "AS-IS" */
/* TO THE RECIPIENT WITHOUT WARRANTY OF ANY KIND, INCLUDING ANY */
/* WARRANTIES OF PERFORMANCE OR MERCHANTABILITY OR FITNESS FOR A */
/* PARTICULAR USE OR PURPOSE (AS SET FORTH IN UNITED STATES UCC */
/* SECTIONS 2312-2313) OR FOR ANY PURPOSE WHATSOEVER, FOR THE */
/* SOFTWARE AND RELATED MATERIALS, HOWEVER USED. */
/* IN NO EVENT SHALL CALTECH, ITS JET PROPULSION LABORATORY, OR NASA */
/* BE LIABLE FOR ANY DAMAGES AND/OR COSTS, INCLUDING, BUT NOT */
/* LIMITED TO, INCIDENTAL OR CONSEQUENTIAL DAMAGES OF ANY KIND, */
/* INCLUDING ECONOMIC DAMAGE OR INJURY TO PROPERTY AND LOST PROFITS, */
/* REGARDLESS OF WHETHER CALTECH, JPL, OR NASA BE ADVISED, HAVE */
/* REASON TO KNOW, OR, IN FACT, SHALL KNOW OF THE POSSIBILITY. */
/* RECIPIENT BEARS ALL RISK RELATING TO QUALITY AND PERFORMANCE OF */
/* THE SOFTWARE AND ANY RELATED MATERIALS, AND AGREES TO INDEMNIFY */
/* CALTECH AND NASA FOR ALL THIRD-PARTY CLAIMS RESULTING FROM THE */
/* ACTIONS OF RECIPIENT IN THE USE OF THE SOFTWARE. */
/* $ Required_Reading */
/* None. */
/* $ Keywords */
/* SPK */
/* $ Declarations */
/* $ Brief_I/O */
/* VARIABLE I/O DESCRIPTION */
/* -------- --- -------------------------------------------------- */
/* ETOBS I Epoch of a signal at some observer */
/* OBS I NAIF-id of some observer */
/* DIR I Direction the signal travels ( '->' or '<-' ) */
/* TARG I NAIF-id of the target object */
/* ETTARG O Epoch of the signal at the target */
/* ELAPSD O Time between transmit and receipt of the signal */
/* $ Detailed_Input */
/* ETOBS is an epoch expressed in ephemeris second (TDB) */
/* past the epoch of the J2000 reference system. */
/* This is the time at which an electromagnetic */
/* signal is "at" the observer. */
/* OBS is the NAIF-id of some observer. */
/* DIR is the direction the signal travels. The */
/* acceptable values are '->' and '<-'. When */
/* you read the calling sequence from left to */
/* right, the "arrow" given by DIR indicates */
/* which way the electromagnetic signal is travelling. */
/* If the argument list reads as below, */
/* ..., OBS, '->', TARG, ... */
/* the signal is travelling from the observer to the */
/* target. */
/* If the argument reads as */
/* ..., OBS, '<-', TARG */
/* the signal is travelling from the target to */
/* the observer. */
/* TARG is the NAIF-id of the target. */
/* $ Detailed_Output */
/* ETTARG is the epoch expressed in ephemeris seconds (TDB) */
/* past the epoch of the J2000 reference system */
/* at which the electromagnetic signal is "at" the */
/* target body. */
/* Note ETTARG is computed using only Newtonian */
/* assumptions about the propagation of light. */
/* ELAPSD is the number of ephemeris seconds (TDB) between */
/* transmission and receipt of the signal. */
/* ELAPSD = DABS( ETOBS - ETTARG ) */
/* $ Parameters */
/* None. */
/* $ Files */
/* None. */
/* $ Exceptions */
/* 1) If DIR is not one of '->' or '<-' the error */
/* 'SPICE(BADDIRECTION)' will be signalled. In this case */
/* ETTARG and ELAPSD will not be altered from their */
/* input values. */
/* 2) If insufficient ephemeris information is available to */
/* compute the outputs ETTARG and ELAPSD, or if observer */
/* or target is not recognized, the problems is diagnosed */
/* by a routine in the call tree of this routine. */
/* In this case, the value of ETTARG will be set to ETOBS */
/* and ELAPSD will be set to zero. */
/* $ Particulars */
/* Suppose a radio signal travels between two solar system */
/* objects. Given an ephemeris for the two objects, which way */
/* the signal is travelling, and the time when the signal is */
/* "at" at one of the objects (the observer OBS), this routine */
/* determines when the signal is "at" the other object (the */
/* target TARG). It also returns the elapsed time between */
/* transmission and receipt of the signal. */
/* $ Examples */
/* Example 1. */
/* ---------- */
/* Suppose a signal is transmitted at time ET from the Goldstone */
/* tracking site (id-code 399001) to a spacecraft whose id-code */
/* is -77. */
/* signal travelling to spacecraft */
/* * -._.-._.-._.-._.-._.-._.-._.-._.-> * */
/* Goldstone (OBS=399001) Spacecraft (TARG = -77) */
/* at epoch ETOBS(given) at epoch ETTARG(unknown) */
/* Assuming that all of the required SPICE kernels have been */
/* loaded, the code fragment below shows how to compute the */
/* time (ARRIVE) at which the signal arrives at the spacecraft */
/* and how long (HOWLNG) it took the signal to reach the spacecraft. */
/* (Note that we display the arrival time as the number of seconds */
/* past J2000.) */
/* OBS = 399001 */
/* TARG = -77 */
/* ETOBS = ET */
/* CALL LTIME ( ETOBS, OBS, '->', TARG, ARRIVE, HOWLNG ) */
/* CALL ETCAL */
/* WRITE (*,*) 'The signal arrived at time: ', ARRIVE */
/* WRITE (*,*) 'It took ', HOWLNG, ' seconds to get there.' */
/* Example 2. */
/* ---------- */
/* Suppose a signal is received at the Goldstone tracking sight */
/* at epoch ET from the spacecraft of the previous example. */
/* signal sent from spacecraft */
/* * <-._.-._.-._.-._.-._.-._.-._.-._.- * */
/* Goldstone (OBS=399001) Spacecraft (TARG = -77) */
/* at epoch ETOBS(given) at epoch ETTARG(unknown) */
/* Again assuming that all the required kernels have been loaded */
/* the code fragment below computes the epoch at which the */
/* signal was transmitted from the spacecraft. */
/* OBS = 399001 */
/* TARG = -77 */
/* ETOBS = ET */
/* CALL LTIME ( ETOBS, OBS, '<-', TARG, SENT, HOWLNG ) */
/* CALL ETCAL */
/* WRITE (*,*) 'The signal was transmitted at: ', SENT */
/* WRITE (*,*) 'It took ', HOWLNG, ' seconds to get here.' */
/* EXAMPLE 3 */
/* --------- */
/* Suppose there is a transponder on board the spacecraft of */
/* the previous examples that transmits a signal back to the */
/* sender exactly 1 microsecond after a signal arrives at */
/* the spacecraft. If we send a signal from Goldstone */
/* to the spacecraft and wait to receive it at Canberra. */
/* What will be the epoch at which the return signal arrives */
/* in Canberra? ( The id-code for Canberra is 399002 ). */
/* Again, assuming we've loaded all the necessary kernels, */
/* the fragment below will give us the answer. */
/* GSTONE = 399001 */
/* SC = -77 */
/* CANBER = 399002 */
/* ETGOLD = ET */
/* CALL LTIME ( ETGOLD, GSTONE, '->', SC, SCGET, LT1 ) */
/* Account for the microsecond delay between receipt and transmit */
/* SCSEND = SCGET + 0.000001 */
/* CALL LTIME ( SCSEND, SC, '->', CANBER, ETCANB, LT2 ) */
/* RNDTRP = ETCANB - ETGOLD */
/* WRITE (*,*) 'The signal arrives in Canberra at: ', ETCANB */
/* WRITE (*,*) 'Round trip time for the signal was: ', RNDTRP */
/* $ Restrictions */
/* None. */
/* $ Author_and_Institution */
/* W.L. Taber (JPL) */
/* $ Literature_References */
/* None. */
/* $ Version */
/* - SPICELIB Version 1.1.2, 22-SEP-2004 (EDW) */
/* Placed Copyright after Abstract. */
/* - SPICELIB Version 1.1.1, 18-NOV-1996 (WLT) */
/* Errors in the examples section were corrected. */
/* - SPICELIB Version 1.1.0, 10-JUL-1996 (WLT) */
/* Added Copyright Notice to the header. */
/* - SPICELIB Version 1.0.0, 10-NOV-1995 (WLT) */
/* -& */
/* $ Index_Entries */
/* Compute uplink and downlink light time */
/* -& */
/* SPICELIB Functions */
/* Local Variables */
if (return_()) {
return 0;
}
chkin_("LTIME", (ftnlen)5);
/* First perform the obvious error check. */
if (s_cmp(dir, "->", (ftnlen)2, (ftnlen)2) != 0 && s_cmp(dir, "<-", (
ftnlen)2, (ftnlen)2) != 0) {
setmsg_("The direction specifier for the signal was '#' it must be "
"either '->' or '<-'. ", (ftnlen)80);
r__ = rtrim_(dir, (ftnlen)2);
errch_("#", dir, (ftnlen)1, r__);
sigerr_("SPICE(BADDIRECTION)", (ftnlen)19);
chkout_("LTIME", (ftnlen)5);
return 0;
}
/* We need two constants, the speed of light and the id-code */
/* for the solar system barycenter. */
c__ = clight_();
bcentr = 0;
myet = *etobs;
/* First get the barycenter relative states of the observer */
/* and target. */
spkgeo_(obs, &myet, "J2000", &bcentr, sobs, <, (ftnlen)5);
spkgeo_(targ, &myet, "J2000", &bcentr, starg, <, (ftnlen)5);
*elapsd = vdist_(sobs, starg) / c__;
/* The rest is straight forward. We either add the elapsed */
/* time to get the next state or subtract the elapsed time. */
/* This depends on whether we are receiving or transmitting */
/* at the observer. */
/* Note that 3 iterations as performed here gives us */
/* Newtonian accuracy to the nanosecond level for all */
/* known objects in the solar system. The ephemeris */
/* is certain to be much worse than this. */
if (s_cmp(dir, "->", (ftnlen)2, (ftnlen)2) == 0) {
*ettarg = myet + *elapsd;
spkgeo_(targ, ettarg, "J2000", &bcentr, starg, <, (ftnlen)5);
*elapsd = vdist_(sobs, starg) / c__;
*ettarg = myet + *elapsd;
spkgeo_(targ, ettarg, "J2000", &bcentr, starg, <, (ftnlen)5);
*elapsd = vdist_(sobs, starg) / c__;
*ettarg = myet + *elapsd;
spkgeo_(targ, ettarg, "J2000", &bcentr, starg, <, (ftnlen)5);
*elapsd = vdist_(sobs, starg) / c__;
*ettarg = myet + *elapsd;
} else {
*ettarg = myet - *elapsd;
spkgeo_(targ, ettarg, "J2000", &bcentr, starg, <, (ftnlen)5);
*elapsd = vdist_(sobs, starg) / c__;
*ettarg = myet - *elapsd;
spkgeo_(targ, ettarg, "J2000", &bcentr, starg, <, (ftnlen)5);
*elapsd = vdist_(sobs, starg) / c__;
*ettarg = myet - *elapsd;
spkgeo_(targ, ettarg, "J2000", &bcentr, starg, <, (ftnlen)5);
*elapsd = vdist_(sobs, starg) / c__;
*ettarg = myet - *elapsd;
}
if (failed_()) {
*ettarg = myet;
*elapsd = 0.;
}
chkout_("LTIME", (ftnlen)5);
return 0;
} /* ltime_ */
/* $Procedure VREL ( Vector relative difference, 3 dimensions ) */
doublereal vrel_(doublereal *v1, doublereal *v2)
{
/* System generated locals */
doublereal ret_val, d__1, d__2;
/* Local variables */
extern doublereal vdist_(doublereal *, doublereal *), vnorm_(doublereal *)
;
doublereal denorm, nunorm;
/* $ Abstract */
/* Return the relative difference between two 3-dimensional vectors. */
/* $ Disclaimer */
/* THIS SOFTWARE AND ANY RELATED MATERIALS WERE CREATED BY THE */
/* CALIFORNIA INSTITUTE OF TECHNOLOGY (CALTECH) UNDER A U.S. */
/* GOVERNMENT CONTRACT WITH THE NATIONAL AERONAUTICS AND SPACE */
/* ADMINISTRATION (NASA). THE SOFTWARE IS TECHNOLOGY AND SOFTWARE */
/* PUBLICLY AVAILABLE UNDER U.S. EXPORT LAWS AND IS PROVIDED "AS-IS" */
/* TO THE RECIPIENT WITHOUT WARRANTY OF ANY KIND, INCLUDING ANY */
/* WARRANTIES OF PERFORMANCE OR MERCHANTABILITY OR FITNESS FOR A */
/* PARTICULAR USE OR PURPOSE (AS SET FORTH IN UNITED STATES UCC */
/* SECTIONS 2312-2313) OR FOR ANY PURPOSE WHATSOEVER, FOR THE */
/* SOFTWARE AND RELATED MATERIALS, HOWEVER USED. */
/* IN NO EVENT SHALL CALTECH, ITS JET PROPULSION LABORATORY, OR NASA */
/* BE LIABLE FOR ANY DAMAGES AND/OR COSTS, INCLUDING, BUT NOT */
/* LIMITED TO, INCIDENTAL OR CONSEQUENTIAL DAMAGES OF ANY KIND, */
/* INCLUDING ECONOMIC DAMAGE OR INJURY TO PROPERTY AND LOST PROFITS, */
/* REGARDLESS OF WHETHER CALTECH, JPL, OR NASA BE ADVISED, HAVE */
/* REASON TO KNOW, OR, IN FACT, SHALL KNOW OF THE POSSIBILITY. */
/* RECIPIENT BEARS ALL RISK RELATING TO QUALITY AND PERFORMANCE OF */
/* THE SOFTWARE AND ANY RELATED MATERIALS, AND AGREES TO INDEMNIFY */
/* CALTECH AND NASA FOR ALL THIRD-PARTY CLAIMS RESULTING FROM THE */
/* ACTIONS OF RECIPIENT IN THE USE OF THE SOFTWARE. */
/* $ Required_Reading */
/* None. */
/* $ Keywords */
/* MATH */
/* VECTOR */
/* $ Declarations */
/* $ Brief_I/O */
/* Variable I/O Description */
/* -------- --- -------------------------------------------------- */
/* V1,V2 I Input vectors. */
/* $ Detailed_Input */
/* V1, V2 are two 3-dimensional vectors for which the */
/* relative difference is to be computed. */
/* $ Detailed_Output */
/* VREL is the relative difference between V1 and V2. */
/* It is defined as: */
/* || V1 - V2 || */
/* VREL = ---------------------- */
/* MAX ( ||V1||, ||V2|| ) */
/* where || X || indicates the Euclidean norm of */
/* the vector X. */
/* VREL assumes values in the range [0,2]. If both */
/* V1 and V2 are zero vectors then VREL is defined */
/* to be zero. */
/* $ Parameters */
/* None. */
/* $ Exceptions */
/* Error free. */
/* If both V1 and V2 are zero vectors then VREL is defined */
/* to be zero. */
/* $ Files */
/* None. */
/* $ Particulars */
/* This function computes the relative difference between two */
/* 3-dimensional vectors as defined above. */
/* The function VRELG may be used to find the relative difference */
/* for two vectors of general dimension. */
/* $ Examples */
/* This example code fragment computes the relative difference */
/* between the geometric and light time corrected state of Io */
/* with respect to Voyager 2 at a given UTC time. */
/* C */
/* C The NAIF integer code for Io is 501 and the code for */
/* C Voyager 2 is -32. */
/* C */
/* INTEGER IO */
/* PARAMETER ( IO = 501 ) */
/* INTEGER VG2 */
/* PARAMETER ( VG2 = -32 ) */
/* C */
/* C Spicelib function */
/* C */
/* DOUBLE PRECISION VREL */
/* C */
/* C Local variables */
/* C */
/* DOUBLE PRECISION STATE ( 6 ) */
/* DOUBLE PRECISION POS1 ( 3 ) */
/* DOUBLE PRECISION POS2 ( 3 ) */
/* DOUBLE PRECISION DIFF */
/* DOUBLE PRECISION LT */
/* DOUBLE PRECISION ET */
/* INTEGER HANDLE */
/* CHARACTER*(20) UTC */
/* DATA UTC / '1979 JUN 25 12:00:00' / */
/* C */
/* C Load the sample SPK ephemeris file. */
/* C */
/* CALL SPKLEF ( 'VG2_JUP.BSP', HANDLE ) */
/* C */
/* C Convert the UTC time string to ephemeris time. */
/* C */
/* CALL UTC2ET ( UTC, ET ) */
/* C */
/* C First calculate the geometric state and then the light */
/* C time corrected state. */
/* C */
/* CALL SPKEZ ( IO, ET, 'J2000', 'NONE', VG2, STATE, LT ) */
/* CALL VEQU ( STATE, POS1 ) */
/* CALL SPKEZ ( IO, ET, 'J2000', 'LT', VG2, STATE, LT ) */
/* CALL VEQU ( STATE, POS2 ) */
/* C */
/* C Call VREL to find the relative difference between the */
/* C two states. */
/* C */
/* DIFF = VREL ( POS1, POS2 ) */
/* . */
/* . */
/* . */
/* $ Restrictions */
/* None. */
/* $ Literature_References */
/* None. */
/* $ Author_and_Institution */
/* J.M. Lynch (JPL) */
/* $ Version */
/* - SPICELIB Version 1.0.0, 15-JUN-1992 (JML) */
/* -& */
/* $ Index_Entries */
/* relative difference of 3-dimensional vectors */
/* -& */
/* SPICELIB functions */
/* Local variables */
/* If the numerator is zero then set VREL equal to zero. Otherwise, */
/* perform the rest of the calculation. */
/* This handles the case where both vectors are zero vectors since */
/* the distance between them will be zero. */
nunorm = vdist_(v1, v2);
if (nunorm == 0.) {
ret_val = 0.;
} else {
/* Computing MAX */
d__1 = vnorm_(v1), d__2 = vnorm_(v2);
denorm = max(d__1,d__2);
ret_val = nunorm / denorm;
}
return ret_val;
} /* vrel_ */
/* $Procedure SUBPT ( Sub-observer point ) */
/* Subroutine */ int subpt_(char *method, char *target, doublereal *et, char *
abcorr, char *obsrvr, doublereal *spoint, doublereal *alt, ftnlen
method_len, ftnlen target_len, ftnlen abcorr_len, ftnlen obsrvr_len)
{
/* Initialized data */
static doublereal origin[3] = { 0.,0.,0. };
doublereal radii[3];
extern /* Subroutine */ int chkin_(char *, ftnlen), errch_(char *, char *,
ftnlen, ftnlen);
logical found;
extern doublereal vdist_(doublereal *, doublereal *);
extern /* Subroutine */ int spkez_(integer *, doublereal *, char *, char *
, integer *, doublereal *, doublereal *, ftnlen, ftnlen);
extern logical eqstr_(char *, char *, ftnlen, ftnlen);
extern /* Subroutine */ int bods2c_(char *, integer *, logical *, ftnlen);
integer obscde;
doublereal lt;
extern /* Subroutine */ int bodvcd_(integer *, char *, integer *, integer
*, doublereal *, ftnlen);
integer frcode;
extern /* Subroutine */ int cidfrm_(integer *, integer *, char *, logical
*, ftnlen);
integer nradii;
char frname[80];
integer trgcde;
extern /* Subroutine */ int nearpt_(doublereal *, doublereal *,
doublereal *, doublereal *, doublereal *, doublereal *), sigerr_(
char *, ftnlen), chkout_(char *, ftnlen), setmsg_(char *, ftnlen);
doublereal tstate[6];
extern logical return_(void);
extern /* Subroutine */ int vminus_(doublereal *, doublereal *), surfpt_(
doublereal *, doublereal *, doublereal *, doublereal *,
doublereal *, doublereal *, logical *);
doublereal pos[3];
/* $ Abstract */
/* Deprecated: This routine has been superseded by the SPICELIB */
/* routine SUBPNT. This routine is supported for purposes of */
/* backward compatibility only. */
/* Compute the rectangular coordinates of the sub-observer point on */
/* a target body at a particular epoch, optionally corrected for */
/* planetary (light time) and stellar aberration. Return these */
/* coordinates expressed in the body-fixed frame associated with the */
/* target body. Also, return the observer's altitude above the */
/* target body. */
/* $ Disclaimer */
/* THIS SOFTWARE AND ANY RELATED MATERIALS WERE CREATED BY THE */
/* CALIFORNIA INSTITUTE OF TECHNOLOGY (CALTECH) UNDER A U.S. */
/* GOVERNMENT CONTRACT WITH THE NATIONAL AERONAUTICS AND SPACE */
/* ADMINISTRATION (NASA). THE SOFTWARE IS TECHNOLOGY AND SOFTWARE */
/* PUBLICLY AVAILABLE UNDER U.S. EXPORT LAWS AND IS PROVIDED "AS-IS" */
/* TO THE RECIPIENT WITHOUT WARRANTY OF ANY KIND, INCLUDING ANY */
/* WARRANTIES OF PERFORMANCE OR MERCHANTABILITY OR FITNESS FOR A */
/* PARTICULAR USE OR PURPOSE (AS SET FORTH IN UNITED STATES UCC */
/* SECTIONS 2312-2313) OR FOR ANY PURPOSE WHATSOEVER, FOR THE */
/* SOFTWARE AND RELATED MATERIALS, HOWEVER USED. */
/* IN NO EVENT SHALL CALTECH, ITS JET PROPULSION LABORATORY, OR NASA */
/* BE LIABLE FOR ANY DAMAGES AND/OR COSTS, INCLUDING, BUT NOT */
/* LIMITED TO, INCIDENTAL OR CONSEQUENTIAL DAMAGES OF ANY KIND, */
/* INCLUDING ECONOMIC DAMAGE OR INJURY TO PROPERTY AND LOST PROFITS, */
/* REGARDLESS OF WHETHER CALTECH, JPL, OR NASA BE ADVISED, HAVE */
/* REASON TO KNOW, OR, IN FACT, SHALL KNOW OF THE POSSIBILITY. */
/* RECIPIENT BEARS ALL RISK RELATING TO QUALITY AND PERFORMANCE OF */
/* THE SOFTWARE AND ANY RELATED MATERIALS, AND AGREES TO INDEMNIFY */
/* CALTECH AND NASA FOR ALL THIRD-PARTY CLAIMS RESULTING FROM THE */
/* ACTIONS OF RECIPIENT IN THE USE OF THE SOFTWARE. */
/* $ Required_Reading */
/* FRAMES */
/* PCK */
/* SPK */
/* TIME */
/* $ Keywords */
/* GEOMETRY */
/* $ Declarations */
/* $ Brief_I/O */
/* Variable I/O Description */
/* -------- --- -------------------------------------------------- */
/* METHOD I Computation method. */
/* TARGET I Name of target body. */
/* ET I Epoch in ephemeris seconds past J2000 TDB. */
/* ABCORR I Aberration correction. */
/* OBSRVR I Name of observing body. */
/* SPOINT O Sub-observer point on the target body. */
/* ALT O Altitude of the observer above the target body. */
/* $ Detailed_Input */
/* METHOD is a short string specifying the computation method */
/* to be used. The choices are: */
/* 'Near point' The sub-observer point is */
/* defined as the nearest point on */
/* the target relative to the */
/* observer. */
/* 'Intercept' The sub-observer point is */
/* defined as the target surface */
/* intercept of the line */
/* containing the observer and the */
/* target's center. */
/* In both cases, the intercept computation treats the */
/* surface of the target body as a triaxial ellipsoid. */
/* The ellipsoid's radii must be available in the kernel */
/* pool. */
/* Neither case nor white space are significant in */
/* METHOD. For example, the string ' NEARPOINT' is */
/* valid. */
/* TARGET is the 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. This routine assumes */
/* that this body is modeled by a tri-axial ellipsoid, */
/* and that a PCK file containing its radii has been */
/* loaded into the kernel pool via FURNSH. */
/* ET is the epoch in ephemeris seconds past J2000 at which */
/* the sub-observer point on the target body is to be */
/* computed. */
/* ABCORR indicates the aberration corrections to be applied */
/* when computing the observer-target state. ABCORR */
/* may be any of the following. */
/* 'NONE' Apply no correction. Return the */
/* geometric sub-observer point on the */
/* target body. */
/* 'LT' Correct for planetary (light time) */
/* aberration. Both the state and rotation */
/* of the target body are corrected for */
/* light time. */
/* 'LT+S' Correct for planetary (light time) and */
/* stellar aberrations. Both the state and */
/* rotation of the target body are */
/* corrected for light time. */
/* 'CN' Converged Newtonian light time */
/* corrections. This is the same as LT */
/* corrections but with further iterations */
/* to a converged Newtonian light time */
/* solution. Given that relativistic */
/* effects may be as large as the higher */
/* accuracy achieved by this computation, */
/* this is correction is seldom worth the */
/* additional computations required unless */
/* the user incorporates additional */
/* relativistic corrections. Both the */
/* state and rotation of the target body */
/* are corrected for light time. */
/* 'CN+S' Converged Newtonian light time */
/* corrections and stellar aberration. */
/* Both the state and rotation of the */
/* target body are corrected for light */
/* time. */
/* OBSRVR is the name of the observing body. This is typically */
/* a spacecraft, the earth, or a surface point on the */
/* earth. 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. */
/* $ Detailed_Output */
/* SPOINT is the sub-observer point on the target body at ET */
/* expressed relative to the body-fixed frame of the */
/* target body. */
/* The sub-observer point is defined either as the point */
/* on the target body that is closest to the observer, */
/* or the target surface intercept of the line from the */
/* observer to the target's center; the input argument */
/* METHOD selects the definition to be used. */
/* The body-fixed frame, which is time-dependent, is */
/* evaluated at ET if ABCORR is 'NONE'; otherwise the */
/* frame is evaluated at ET-LT, where LT is the one-way */
/* light time from target to observer. */
/* The state of the target body is corrected for */
/* aberration as specified by ABCORR; the corrected */
/* state is used in the geometric computation. As */
/* indicated above, the rotation of the target is */
/* retarded by one-way light time if ABCORR specifies */
/* that light time correction is to be done. */
/* ALT is the "altitude" of the observer above the target */
/* body. When METHOD specifies a "near point" */
/* computation, ALT is truly altitude in the standard */
/* geometric sense: the length of a segment dropped from */
/* the observer to the target's surface, such that the */
/* segment is perpendicular to the surface at the */
/* contact point SPOINT. */
/* When METHOD specifies an "intercept" computation, ALT */
/* is still the length of the segment from the observer */
/* to the surface point SPOINT, but this segment in */
/* general is not perpendicular to the surface. */
/* $ Parameters */
/* None. */
/* $ Exceptions */
/* If any of the listed errors occur, the output arguments are */
/* left unchanged. */
/* 1) If the input argument METHOD is not recognized, the error */
/* SPICE(DUBIOUSMETHOD) is signaled. */
/* 2) If either of the input body names TARGET or OBSRVR cannot be */
/* mapped to NAIF integer codes, the error SPICE(IDCODENOTFOUND) */
/* is signaled. */
/* 3) If OBSRVR and TARGET map to the same NAIF integer ID codes, the */
/* error SPICE(BODIESNOTDISTINCT) is signaled. */
/* 4) If frame definition data enabling the evaluation of the state */
/* of the target relative to the observer in target body-fixed */
/* coordinates have not been loaded prior to calling SUBPT, the */
/* error will be diagnosed and signaled by a routine in the call */
/* tree of this routine. */
/* 5) If the specified aberration correction is not recognized, the */
/* error will be diagnosed and signaled by a routine in the call */
/* tree of this routine. */
/* 6) If insufficient ephemeris data have been loaded prior to */
/* calling SUBPT, the error will be diagnosed and signaled by a */
/* routine in the call tree of this routine. */
/* 7) If the triaxial radii of the target body have not been loaded */
/* into the kernel pool prior to calling SUBPT, the error will be */
/* diagnosed and signaled by a routine in the call tree of this */
/* routine. */
/* 8) The target must be an extended body: if any of the radii of */
/* the target body are non-positive, the error will be diagnosed */
/* and signaled by routines in the call tree of this routine. */
/* 9) If PCK data supplying a rotation model for the target body */
/* have not been loaded prior to calling SUBPT, the error will be */
/* diagnosed and signaled by a routine in the call tree of this */
/* routine. */
/* $ Files */
/* Appropriate SPK, PCK, and frame kernels must be loaded */
/* prior by the calling program before this routine is called. */
/* The following data are required: */
/* - SPK data: ephemeris data for target and observer 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. */
/* - PCK data: triaxial radii for the target body must be loaded */
/* into the kernel pool. Typically this is done by loading a */
/* text PCK file via FURNSH. */
/* - Further PCK data: rotation data for the target body must */
/* be loaded. These may be provided in a text or binary PCK */
/* file. Either type of file may be loaded via FURNSH. */
/* - Frame data: if a frame definition is required to convert */
/* the observer and target states to the body-fixed frame of */
/* the target, that definition must be available in the kernel */
/* pool. Typically the definition is supplied by loading a */
/* frame kernel via FURNSH. */
/* In all cases, kernel data are normally loaded once per program */
/* run, NOT every time this routine is called. */
/* $ Particulars */
/* SUBPT computes the sub-observer point on a target body. */
/* (The sub-observer point is commonly called the sub-spacecraft */
/* point when the observer is a spacecraft.) SUBPT also */
/* determines the altitude of the observer above the target body. */
/* There are two different popular ways to define the sub-observer */
/* point: "nearest point on target to observer" or "target surface */
/* intercept of line containing observer and target." These */
/* coincide when the target is spherical and generally are distinct */
/* otherwise. */
/* When comparing sub-point computations with results from sources */
/* other than SPICE, it's essential to make sure the same geometric */
/* definitions are used. */
/* $ Examples */
/* The numerical results shown for this example 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. */
/* In the following example program, the file */
/* spk_m_031103-040201_030502.bsp */
/* is a binary SPK file containing data for Mars Global Surveyor, */
/* Mars, and the Sun for a time interval bracketing the date */
/* 2004 JAN 1 12:00:00 UTC. */
/* pck00007.tpc is a planetary constants kernel file containing */
/* radii and rotation model constants. naif0007.tls is a */
/* leapseconds kernel. */
/* Find the sub-observer point of the Mars Global Surveyor (MGS) */
/* spacecraft on Mars for a specified time. Perform the computation */
/* twice, using both the "intercept" and "near point" options. */
/* IMPLICIT NONE */
/* CHARACTER*25 METHOD ( 2 ) */
/* INTEGER I */
/* DOUBLE PRECISION ALT */
/* DOUBLE PRECISION DPR */
/* DOUBLE PRECISION ET */
/* DOUBLE PRECISION LAT */
/* DOUBLE PRECISION LON */
/* DOUBLE PRECISION RADIUS */
/* DOUBLE PRECISION SPOINT ( 3 ) */
/* DATA METHOD / 'Intercept', 'Near point' / */
/* C */
/* C Load kernel files. */
/* C */
/* CALL FURNSH ( 'naif0007.tls' ) */
/* CALL FURNSH ( 'pck00007.tpc' ) */
/* CALL FURNSH ( 'spk_m_031103-040201_030502.bsp' ) */
/* C */
/* C Convert the UTC request time to ET (seconds past */
/* C J2000, TDB). */
/* C */
/* CALL STR2ET ( '2004 JAN 1 12:00:00', ET ) */
/* C */
/* C Compute sub-spacecraft point using light time and stellar */
/* C aberration corrections. Use the "target surface intercept" */
/* C definition of sub-spacecraft point on the first loop */
/* C iteration, and use the "near point" definition on the */
/* C second. */
/* C */
/* DO I = 1, 2 */
/* CALL SUBPT ( METHOD(I), */
/* . 'MARS', ET, 'LT+S', */
/* . 'MGS', SPOINT, ALT ) */
/* C */
/* C Convert rectangular coordinates to planetocentric */
/* C latitude and longitude. Convert radians to degrees. */
/* C */
/* CALL RECLAT ( SPOINT, RADIUS, LON, LAT ) */
/* LON = LON * DPR () */
/* LAT = LAT * DPR () */
/* C */
/* C Write the results. */
/* C */
/* WRITE (*,*) ' ' */
/* WRITE (*,*) 'Computation method: ', METHOD(I) */
/* WRITE (*,*) ' ' */
/* WRITE (*,*) ' Radius (km) = ', RADIUS */
/* WRITE (*,*) ' Planetocentric Latitude (deg) = ', LAT */
/* WRITE (*,*) ' Planetocentric Longitude (deg) = ', LON */
/* WRITE (*,*) ' Altitude (km) = ', ALT */
/* WRITE (*,*) ' ' */
/* END DO */
/* END */
/* When this program is executed, the output will be: */
/* Computation method: Intercept */
/* Radius (km) = 3387.97077 */
/* Planetocentric Latitude (deg) = -39.7022724 */
/* Planetocentric Longitude (deg) = -159.226663 */
/* Altitude (km) = 373.173506 */
/* Computation method: Near point */
/* Radius (km) = 3387.9845 */
/* Planetocentric Latitude (deg) = -39.6659329 */
/* Planetocentric Longitude (deg) = -159.226663 */
/* Altitude (km) = 373.166636 */
/* $ Restrictions */
/* None. */
/* $ Literature_References */
/* None. */
/* $ Author_and_Institution */
/* C.H. Acton (JPL) */
/* N.J. Bachman (JPL) */
/* J.E. McLean (JPL) */
/* $ Version */
/* - SPICELIB Version 1.2.3, 18-MAY-2010 (BVS) */
/* Index line now states that this routine is deprecated. */
/* - SPICELIB Version 1.2.2, 17-MAR-2009 (EDW) */
/* Typo correction in Required_Reading, changed */
/* FRAME to FRAMES. */
/* - SPICELIB Version 1.2.1, 07-FEB-2008 (NJB) */
/* Abstract now states that this routine is deprecated. */
/* - SPICELIB Version 1.2.0, 24-OCT-2005 (NJB) */
/* Replaced call to BODVAR with call to BODVCD. */
/* - SPICELIB Version 1.1.0, 21-JUL-2004 (EDW) */
/* Changed BODN2C call to BODS2C giving the routine */
/* the capability to accept string representations of */
/* interger IDs for TARGET and OBSRVR. */
/* - SPICELIB Version 1.0.1, 27-JUL-2003 (NJB) (CHA) */
/* Various header corrections were made. The example program */
/* was upgraded to use real kernels, and the program's output is */
/* shown. */
/* - SPICELIB Version 1.0.0, 03-SEP-1999 (NJB) (JEM) */
/* -& */
/* $ Index_Entries */
/* DEPRECATED sub-observer point */
/* -& */
/* SPICELIB functions */
/* Local parameters */
/* Local variables */
/* Saved variables */
/* Initial values */
/* Standard SPICE error handling. */
if (return_()) {
return 0;
} else {
chkin_("SUBPT", (ftnlen)5);
}
/* Obtain integer codes for the target and observer. */
/* Target... */
bods2c_(target, &trgcde, &found, target_len);
if (! found) {
setmsg_("The target, '#', is not a recognized name for an ephemeris "
"object. The cause of this problem may be that you need an up"
"dated version of the SPICE Toolkit. ", (ftnlen)155);
errch_("#", target, (ftnlen)1, target_len);
sigerr_("SPICE(IDCODENOTFOUND)", (ftnlen)21);
chkout_("SUBPT", (ftnlen)5);
return 0;
}
/* ...observer. */
bods2c_(obsrvr, &obscde, &found, obsrvr_len);
if (! found) {
setmsg_("The observer, '#', is not a recognized name for an ephemeri"
"s object. The cause of this problem may be that you need an "
"updated version of the SPICE Toolkit. ", (ftnlen)157);
errch_("#", obsrvr, (ftnlen)1, obsrvr_len);
sigerr_("SPICE(IDCODENOTFOUND)", (ftnlen)21);
chkout_("SUBPT", (ftnlen)5);
return 0;
}
/* Check the input body codes. If they are equal, signal */
/* an error. */
if (obscde == trgcde) {
setmsg_("In computing the sub-observer point, the observing body and"
" target body are the same. Both are #.", (ftnlen)97);
errch_("#", obsrvr, (ftnlen)1, obsrvr_len);
sigerr_("SPICE(BODIESNOTDISTINCT)", (ftnlen)24);
chkout_("SUBPT", (ftnlen)5);
return 0;
}
/* Get the radii of the target body from the kernel pool. */
bodvcd_(&trgcde, "RADII", &c__3, &nradii, radii, (ftnlen)5);
/* Find the name of the body-fixed frame associated with the */
/* target body. We'll want the state of the target relative to */
/* the observer in this body-fixed frame. */
cidfrm_(&trgcde, &frcode, frname, &found, (ftnlen)80);
if (! found) {
setmsg_("No body-fixed frame is associated with target body #; a fra"
"me kernel must be loaded to make this association. Consult "
"the FRAMES Required Reading for details.", (ftnlen)159);
errch_("#", target, (ftnlen)1, target_len);
sigerr_("SPICE(NOFRAME)", (ftnlen)14);
chkout_("SUBPT", (ftnlen)5);
return 0;
}
/* Determine the position of the observer in target */
/* body-fixed coordinates. */
/* - Call SPKEZR to compute the position of the target */
/* body as seen from the observing body and the light time */
/* (LT) between them. SPKEZR returns a state which is */
/* the position and velocity, but we'll only use the position */
/* which is the first three elements. We request that the */
/* coordinates of POS be returned relative to the body fixed */
/* reference frame associated with the target body, using */
/* aberration corrections specified by the input argument */
/* ABCORR. */
/* - Call VMINUS to negate the direction of the vector (POS) */
/* so it will be the position of the observer as seen from */
/* the target body in target body fixed coordinates. */
/* Note that this result is not the same as the result of */
/* calling SPKEZR with the target and observer switched. We */
/* computed the vector FROM the observer TO the target in */
/* order to get the proper light time and stellar aberration */
/* corrections (if requested). Now we need the inverse of */
/* that corrected vector in order to compute the sub-point. */
spkez_(&trgcde, et, frname, abcorr, &obscde, tstate, <, (ftnlen)80,
abcorr_len);
/* Negate the target's state to obtain the position of the observer */
/* relative to the target. */
vminus_(tstate, pos);
/* Find the sub-point and "altitude" (distance from observer to */
/* sub-point) using the specified geometric definition. */
if (eqstr_(method, "Near point", method_len, (ftnlen)10)) {
/* Locate the nearest point to the observer on the target. */
nearpt_(pos, radii, &radii[1], &radii[2], spoint, alt);
} else if (eqstr_(method, "Intercept", method_len, (ftnlen)9)) {
surfpt_(origin, pos, radii, &radii[1], &radii[2], spoint, &found);
/* Since the line in question passes through the center of the */
/* target, there will always be a surface intercept. So we should */
/* never have FOUND = .FALSE. */
if (! found) {
setmsg_("Call to SURFPT returned FOUND=FALSE even though vertex "
"of ray is at target center. This indicates a bug. Please"
" contact NAIF.", (ftnlen)125);
sigerr_("SPICE(BUG)", (ftnlen)10);
chkout_("SUBPT", (ftnlen)5);
return 0;
}
/* SURFPT doesn't compute altitude, so do it here. */
*alt = vdist_(pos, spoint);
} else {
setmsg_("The computation method # was not recognized. Allowed values"
" are \"Near point\" and \"Intercept.\"", (ftnlen)93);
errch_("#", method, (ftnlen)1, method_len);
sigerr_("SPICE(DUBIOUSMETHOD)", (ftnlen)20);
chkout_("SUBPT", (ftnlen)5);
return 0;
}
chkout_("SUBPT", (ftnlen)5);
return 0;
} /* subpt_ */
