/* $Procedure ZZSPKFAP ( SPK function, apparent inertial state ) */
/* Subroutine */ int zzspkfap_(U_fp trgsub, doublereal *et, char *ref, char *
abcorr, doublereal *stobs, doublereal *accobs, doublereal *starg,
doublereal *lt, doublereal *dlt, ftnlen ref_len, ftnlen abcorr_len)
{
/* Initialized data */
static logical pass1 = TRUE_;
static char prvcor[5] = " ";
/* Builtin functions */
integer s_cmp(char *, char *, ftnlen, ftnlen);
/* Subroutine */ int s_copy(char *, char *, ftnlen, ftnlen);
/* Local variables */
extern /* Subroutine */ int vadd_(doublereal *, doublereal *, doublereal *
), vequ_(doublereal *, doublereal *);
static logical xmit;
extern /* Subroutine */ int zzstelab_(logical *, doublereal *, doublereal
*, doublereal *, doublereal *, doublereal *), zzvalcor_(char *,
logical *, ftnlen), zzspkflt_(U_fp, doublereal *, char *, char *,
doublereal *, doublereal *, doublereal *, doublereal *, ftnlen,
ftnlen);
integer refid;
extern /* Subroutine */ int chkin_(char *, ftnlen), errch_(char *, char *,
ftnlen, ftnlen);
doublereal pcorr[3];
static logical uselt;
extern logical failed_(void);
logical attblk[15];
doublereal dpcorr[3], corvel[3];
extern /* Subroutine */ int sigerr_(char *, ftnlen), chkout_(char *,
ftnlen), irfnum_(char *, integer *, ftnlen), setmsg_(char *,
ftnlen);
doublereal corpos[3];
extern logical return_(void);
static logical usestl;
/* $ Abstract */
/* SPICE Private routine intended solely for the support of SPICE */
/* routines. Users should not call this routine directly due */
/* to the volatile nature of this routine. */
/* Given the state and acceleration of an observer relative to the */
/* solar system barycenter, return the state (position and velocity) */
/* of a target body relative to the observer, optionally corrected */
/* for light time and stellar aberration. All input and output */
/* vectors are expressed relative to an inertial reference frame. An */
/* input subroutine provides the state of the target relative to its */
/* center of motion. */
/* $ 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 */
/* SPK */
/* $ Keywords */
/* EPHEMERIS */
/* $ Declarations */
/* $ Abstract */
/* Include file zzabcorr.inc */
/* SPICE private file intended solely for the support of SPICE */
/* routines. Users should not include this file directly due */
/* to the volatile nature of this file */
/* The parameters below define the structure of an aberration */
/* correction attribute block. */
/* $ 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. */
/* $ Parameters */
/* An aberration correction attribute block is an array of logical */
/* flags indicating the attributes of the aberration correction */
/* specified by an aberration correction string. The attributes */
/* are: */
/* - Is the correction "geometric"? */
/* - Is light time correction indicated? */
/* - Is stellar aberration correction indicated? */
/* - Is the light time correction of the "converged */
/* Newtonian" variety? */
/* - Is the correction for the transmission case? */
/* - Is the correction relativistic? */
/* The parameters defining the structure of the block are as */
/* follows: */
/* NABCOR Number of aberration correction choices. */
/* ABATSZ Number of elements in the aberration correction */
/* block. */
/* GEOIDX Index in block of geometric correction flag. */
/* LTIDX Index of light time flag. */
/* STLIDX Index of stellar aberration flag. */
/* CNVIDX Index of converged Newtonian flag. */
/* XMTIDX Index of transmission flag. */
/* RELIDX Index of relativistic flag. */
/* The following parameter is not required to define the block */
/* structure, but it is convenient to include it here: */
/* CORLEN The maximum string length required by any aberration */
/* correction string */
/* $ Author_and_Institution */
/* N.J. Bachman (JPL) */
/* $ Literature_References */
/* None. */
/* $ Version */
/* - SPICELIB Version 1.0.0, 18-DEC-2004 (NJB) */
/* -& */
/* Number of aberration correction choices: */
/* Aberration correction attribute block size */
/* (number of aberration correction attributes): */
/* Indices of attributes within an aberration correction */
/* attribute block: */
/* Maximum length of an aberration correction string: */
/* End of include file zzabcorr.inc */
/* $ Brief_I/O */
/* Variable I/O Description */
/* -------- --- -------------------------------------------------- */
/* TRGSUB I Target body state subroutine. */
/* ET I Observer epoch. */
/* REF I Inertial reference frame of output state. */
/* ABCORR I Aberration correction flag. */
/* STOBS I State of the observer relative to the SSB. */
/* ACCOBS I Acceleration of the observer relative to the SSB. */
/* STARG O State of target. */
/* LT O One way light time between observer and target. */
/* DLT O Derivative of light time with respect to time. */
/* $ Detailed_Input */
/* TRGSUB is the name of an external subroutine that returns */
/* the geometric state of the target body relative to a */
/* center of motion, expressed in the inertial reference */
/* frame REF, at the epoch ET. */
/* The calling sequence of TRGSUB is */
/* SUBROUTINE TRGSUB ( ET, REF, TRGCTR, STATE ) */
/* DOUBLE PRECISION ET */
/* CHARACTER*(*) REF */
/* INTEGER TRGCTR */
/* DOUBLE PRECISION STATE ( 6 ) */
/* The inputs of TRGSUB are ET and REF; the outputs */
/* are TRGCTR and STATE. STATE is the geometric state */
/* of the target relative to the returned center of */
/* motion at ET, expressed in the frame REF. */
/* The target and observer define a state vector whose */
/* position component points from the observer to the */
/* target. */
/* ET is the ephemeris time, expressed as seconds past */
/* J2000 TDB, at which the state of the target body */
/* relative to the observer is to be computed. ET */
/* refers to time at the observer's location. */
/* REF is the inertial reference frame with respect to which */
/* the input state STOBS, the input acceleration ACCOBS, */
/* and the output state STARG are expressed. REF must be */
/* recognized by the SPICE Toolkit. The acceptable */
/* frames are listed in the Frames Required Reading, as */
/* well as in the SPICELIB routine CHGIRF. */
/* Case and blanks are not significant in the string */
/* REF. */
/* ABCORR indicates the aberration corrections to be applied */
/* to the state of the target body to account for one-way */
/* light time and stellar aberration. See the discussion */
/* in the header of SPKEZR for recommendations on */
/* how to choose aberration corrections. */
/* ABCORR may be any of the following: */
/* 'NONE' Apply no correction. Return the */
/* geometric state of the target body */
/* relative to the observer. */
/* The following values of ABCORR apply to the */
/* "reception" case in which photons depart from the */
/* target's location at the light-time corrected epoch */
/* ET-LT and *arrive* at the observer's location at ET: */
/* 'LT' Correct for one-way light time (also */
/* called "planetary aberration") using a */
/* Newtonian formulation. This correction */
/* yields the state of the target at the */
/* moment it emitted photons arriving at */
/* the observer at ET. */
/* The light time correction uses an */
/* iterative solution of the light time */
/* equation (see Particulars for details). */
/* The solution invoked by the 'LT' option */
/* uses one iteration. */
/* 'LT+S' Correct for one-way light time and */
/* stellar aberration using a Newtonian */
/* formulation. This option modifies the */
/* state obtained with the 'LT' option to */
/* account for the observer's velocity */
/* relative to the solar system */
/* barycenter. The result is the apparent */
/* state of the target---the position and */
/* velocity of the target as seen by the */
/* observer. */
/* 'CN' Converged Newtonian light time */
/* correction. In solving the light time */
/* equation, the 'CN' correction iterates */
/* until the solution converges (three */
/* iterations on all supported platforms). */
/* Whether the 'CN+S' solution is */
/* substantially more accurate than the */
/* 'LT' solution depends on the geometry */
/* of the participating objects and on the */
/* accuracy of the input data. In all */
/* cases this routine will execute more */
/* slowly when a converged solution is */
/* computed. See the Particulars section of */
/* SPKEZR for a discussion of precision of */
/* light time corrections. */
/* 'CN+S' Converged Newtonian light time */
/* correction and stellar aberration */
/* correction. */
/* The following values of ABCORR apply to the */
/* "transmission" case in which photons *depart* from */
/* the observer's location at ET and arrive at the */
/* target's location at the light-time corrected epoch */
/* ET+LT: */
/* 'XLT' "Transmission" case: correct for */
/* one-way light time using a Newtonian */
/* formulation. This correction yields the */
/* state of the target at the moment it */
/* receives photons emitted from the */
/* observer's location at ET. */
/* 'XLT+S' "Transmission" case: correct for */
/* one-way light time and stellar */
/* aberration using a Newtonian */
/* formulation This option modifies the */
/* state obtained with the 'XLT' option to */
/* account for the observer's velocity */
/* relative to the solar system */
/* barycenter. The position component of */
/* the computed target state indicates the */
/* direction that photons emitted from the */
/* observer's location must be "aimed" to */
/* hit the target. */
/* 'XCN' "Transmission" case: converged */
/* Newtonian light time correction. */
/* 'XCN+S' "Transmission" case: converged */
/* Newtonian light time correction and */
/* stellar aberration correction. */
/* Neither special nor general relativistic effects are */
/* accounted for in the aberration corrections applied */
/* by this routine. */
/* Case and blanks are not significant in the string */
/* ABCORR. */
/* STOBS is the geometric state of the observer relative to */
/* the solar system barycenter at ET. STOBS is expressed */
/* relative to the reference frame designated by REF. */
/* The target and observer define a state vector whose */
/* position component points from the observer to the */
/* target. */
/* ACCOBS is the geometric acceleration of the observer */
/* relative to the solar system barycenter at ET. This */
/* is the derivative with respect to time of the */
/* velocity portion of STOBS. ACCOBS is expressed */
/* relative to the reference frame designated by REF. */
/* ACCOBS is used for computing stellar aberration */
/* corrected velocity. If stellar aberration corrections */
/* are not specified by ABCORR, ACCOBS is ignored; the */
/* caller need not provide a valid input value in this */
/* case. */
/* $ Detailed_Output */
/* STARG is a Cartesian state vector representing the position */
/* and velocity of the target body relative to the */
/* specified observer. STARG is corrected for the */
/* specified aberrations, and is expressed with respect */
/* to the inertial reference frame designated by REF. */
/* The first three components of STARG represent the x-, */
/* y- and z-components of the target's position; last */
/* three components form the corresponding velocity */
/* vector. */
/* The position component of STARG points from the */
/* observer's location at ET to the aberration-corrected */
/* location of the target. Note that the sense of the */
/* position vector is independent of the direction of */
/* radiation travel implied by the aberration */
/* correction. */
/* Units are always km and km/sec. */
/* LT is the one-way light time between the observer and */
/* target in seconds. If the target state is corrected */
/* for light time, then LT is the one-way light time */
/* between the observer and the light time-corrected */
/* target location. */
/* DLT is the derivative with respect to barycentric */
/* dynamical time of the one way light time between */
/* target and observer: */
/* DLT = d(LT)/d(ET) */
/* DLT can also be described as the rate of change of */
/* one way light time. DLT is unitless, since LT and */
/* ET both have units of TDB seconds. */
/* If the observer and target are at the same position, */
/* then DLT is set to zero. */
/* $ Parameters */
/* None. */
/* $ Exceptions */
/* 1) If the value of ABCORR is not recognized, the error */
/* is diagnosed by a routine in the call tree of this */
/* routine. */
/* 2) If the reference frame requested is not a recognized */
/* inertial reference frame, the error SPICE(BADFRAME) */
/* is signaled. */
/* 3) If the state of the target relative to the solar system */
/* barycenter cannot be computed, the error will be diagnosed */
/* by routines in the call tree of this routine. */
/* 4) If the observer and target are at the same position, */
/* then DLT is set to zero. This situation could arise, */
/* for example, when the observer is Mars and the target */
/* is the Mars barycenter. */
/* $ Files */
/* This routine computes states using SPK files that have been */
/* loaded into the SPICE system, normally via the kernel loading */
/* interface routine FURNSH. Application programs typically load */
/* kernels once before this routine is called, for example during */
/* program initialization; kernels need not be loaded repeatedly. */
/* See the routine FURNSH and the SPK and KERNEL Required Reading */
/* for further information on loading (and unloading) kernels. */
/* If any of the ephemeris data used to compute STARG are expressed */
/* relative to a non-inertial frame in the SPK files providing those */
/* data, additional kernels may be needed to enable the reference */
/* frame transformations required to compute the state. Normally */
/* these additional kernels are PCK files or frame kernels. Any such */
/* kernels must already be loaded at the time this routine is */
/* called. */
/* $ Particulars */
/* This routine supports higher-level routines that can */
/* perform both light time and stellar aberration corrections */
/* and that use target states provided by subroutines rather */
/* than by the conventional, public SPK APIs. For example, this */
/* routine can be used for objects having fixed positions */
/* on the surfaces of planets. */
/* $ Examples */
/* None. */
/* $ Restrictions */
/* 1) This routine must not be called by routines of the SPICE */
/* frame subsystem. It must not be called by any portion of */
/* the SPK subsystem other than the private SPK function-based */
/* component. */
/* 2) The input subroutine TRGSUB must not call this routine */
/* or any of the supporting, private SPK routines */
/* ZZSPKFAT */
/* ZZSPKFAO */
/* ZZSPKFZO */
/* ZZSPKFZT */
/* 3) When possible, the routine SPKGEO should be used instead of */
/* this routine to compute geometric states. SPKGEO introduces */
/* less round-off error when the observer and target have common */
/* center that is closer to both objects than is the solar */
/* system barycenter. */
/* 4) Unlike most other SPK state computation routines, this */
/* routine requires that the output state be relative to an */
/* inertial reference frame. */
/* $ Literature_References */
/* None. */
/* $ Author_and_Institution */
/* N.J. Bachman (JPL) */
/* $ Version */
/* - SPICELIB Version 1.0.0, 04-JUL-2014 (NJB) */
/* Discussion of light time corrections was updated. Assertions */
/* that converged light time corrections are unlikely to be */
/* useful were removed. */
/* - SPICELIB Version 1.0.0, 09-JAN-2011 (NJB) */
/* -& */
/* $ Index_Entries */
/* low-level aberration-corrected state computation */
/* low-level light time and stellar aberration correction */
/* -& */
/* $ Revisions */
/* None. */
/* -& */
/* SPICELIB functions */
/* Local parameters */
/* Local variables */
/* Saved variables */
/* Initial values */
/* Standard SPICE error handling. */
if (return_()) {
return 0;
}
chkin_("ZZSPKFAP", (ftnlen)8);
if (pass1 || s_cmp(abcorr, prvcor, abcorr_len, (ftnlen)5) != 0) {
/* The aberration correction flag differs from the value it */
/* had on the previous call, if any. Analyze the new flag. */
zzvalcor_(abcorr, attblk, abcorr_len);
if (failed_()) {
chkout_("ZZSPKFAP", (ftnlen)8);
return 0;
}
/* The aberration correction flag is recognized; save it. */
s_copy(prvcor, abcorr, (ftnlen)5, abcorr_len);
/* Set logical flags indicating the attributes of the requested */
/* correction: */
/* XMIT is .TRUE. when the correction is for transmitted */
/* radiation. */
/* USELT is .TRUE. when any type of light time correction */
/* (normal or converged Newtonian) is specified. */
/* USECN indicates converged Newtonian light time correction. */
/* The above definitions are consistent with those used by */
/* ZZVALCOR. */
xmit = attblk[4];
uselt = attblk[1];
usestl = attblk[2];
pass1 = FALSE_;
}
/* See if the reference frame is a recognized inertial frame. */
irfnum_(ref, &refid, ref_len);
if (refid == 0) {
setmsg_("The requested frame '#' is not a recognized inertial frame. "
, (ftnlen)60);
errch_("#", ref, (ftnlen)1, ref_len);
sigerr_("SPICE(BADFRAME)", (ftnlen)15);
chkout_("ZZSPKFAP", (ftnlen)8);
return 0;
}
/* Get the state of the target relative to the observer, */
/* optionally corrected for light time. */
zzspkflt_((U_fp)trgsub, et, ref, abcorr, stobs, starg, lt, dlt, ref_len,
abcorr_len);
if (failed_()) {
chkout_("ZZSPKFAP", (ftnlen)8);
return 0;
}
/* If stellar aberration corrections are not needed, we're */
/* already done. */
if (! usestl) {
chkout_("ZZSPKFAP", (ftnlen)8);
return 0;
}
/* Get the stellar aberration correction and its time derivative. */
zzstelab_(&xmit, accobs, &stobs[3], starg, pcorr, dpcorr);
/* Adding the stellar aberration correction to the light */
/* time-corrected target position yields the position corrected for */
/* both light time and stellar aberration. */
vadd_(pcorr, starg, corpos);
vequ_(corpos, starg);
/* Velocity is treated in an analogous manner. */
vadd_(dpcorr, &starg[3], corvel);
vequ_(corvel, &starg[3]);
chkout_("ZZSPKFAP", (ftnlen)8);
return 0;
} /* zzspkfap_ */
/* $Procedure ZZSPKFLT ( SPK function, light time and rate ) */
/* Subroutine */ int zzspkflt_(S_fp trgsub, doublereal *et, char *ref, char *
abcorr, doublereal *stobs, doublereal *starg, doublereal *lt,
doublereal *dlt, ftnlen ref_len, ftnlen abcorr_len)
{
/* Initialized data */
static logical pass1 = TRUE_;
static char prvcor[5] = " ";
/* System generated locals */
doublereal d__1, d__2, d__3, d__4;
/* Builtin functions */
integer s_cmp(char *, char *, ftnlen, ftnlen);
/* Subroutine */ int s_copy(char *, char *, ftnlen, ftnlen);
/* Local variables */
doublereal dist;
extern doublereal vdot_(doublereal *, doublereal *);
static logical xmit;
extern /* Subroutine */ int zzvalcor_(char *, logical *, ftnlen);
doublereal a, b, c__;
integer i__;
extern /* Subroutine */ int vaddg_(doublereal *, doublereal *, integer *,
doublereal *);
integer refid;
extern /* Subroutine */ int chkin_(char *, ftnlen);
doublereal epoch;
extern /* Subroutine */ int errch_(char *, char *, ftnlen, ftnlen);
static logical usecn;
extern /* Subroutine */ int vlcom_(doublereal *, doublereal *, doublereal
*, doublereal *, doublereal *), vsubg_(doublereal *, doublereal *,
integer *, doublereal *);
doublereal lterr;
static logical uselt;
extern doublereal vnorm_(doublereal *);
doublereal prvlt;
extern logical failed_(void);
extern doublereal clight_(void);
logical attblk[15];
extern doublereal touchd_(doublereal *);
extern /* Subroutine */ int sigerr_(char *, ftnlen), chkout_(char *,
ftnlen);
doublereal ctrssb[6];
integer ltsign;
extern /* Subroutine */ int irfnum_(char *, integer *, ftnlen), setmsg_(
char *, ftnlen);
doublereal ssbtrg[6];
integer trgctr;
extern /* Subroutine */ int spkssb_(integer *, doublereal *, char *,
doublereal *, ftnlen);
integer numitr;
extern logical return_(void);
logical usestl;
doublereal sttctr[6];
/* $ Abstract */
/* SPICE Private routine intended solely for the support of SPICE */
/* routines. Users should not call this routine directly due */
/* to the volatile nature of this routine. */
/* Return the state (position and velocity) of a target body */
/* relative to an observer, optionally corrected for light time, */
/* expressed relative to an inertial reference frame. An input */
/* subroutine provides the state of the target relative to its */
/* center of motion. */
/* $ 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 */
/* SPK */
/* $ Keywords */
/* EPHEMERIS */
/* $ Declarations */
/* $ Abstract */
/* Include file zzabcorr.inc */
/* SPICE private file intended solely for the support of SPICE */
/* routines. Users should not include this file directly due */
/* to the volatile nature of this file */
/* The parameters below define the structure of an aberration */
/* correction attribute block. */
/* $ 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. */
/* $ Parameters */
/* An aberration correction attribute block is an array of logical */
/* flags indicating the attributes of the aberration correction */
/* specified by an aberration correction string. The attributes */
/* are: */
/* - Is the correction "geometric"? */
/* - Is light time correction indicated? */
/* - Is stellar aberration correction indicated? */
/* - Is the light time correction of the "converged */
/* Newtonian" variety? */
/* - Is the correction for the transmission case? */
/* - Is the correction relativistic? */
/* The parameters defining the structure of the block are as */
/* follows: */
/* NABCOR Number of aberration correction choices. */
/* ABATSZ Number of elements in the aberration correction */
/* block. */
/* GEOIDX Index in block of geometric correction flag. */
/* LTIDX Index of light time flag. */
/* STLIDX Index of stellar aberration flag. */
/* CNVIDX Index of converged Newtonian flag. */
/* XMTIDX Index of transmission flag. */
/* RELIDX Index of relativistic flag. */
/* The following parameter is not required to define the block */
/* structure, but it is convenient to include it here: */
/* CORLEN The maximum string length required by any aberration */
/* correction string */
/* $ Author_and_Institution */
/* N.J. Bachman (JPL) */
/* $ Literature_References */
/* None. */
/* $ Version */
/* - SPICELIB Version 1.0.0, 18-DEC-2004 (NJB) */
/* -& */
/* Number of aberration correction choices: */
/* Aberration correction attribute block size */
/* (number of aberration correction attributes): */
/* Indices of attributes within an aberration correction */
/* attribute block: */
/* Maximum length of an aberration correction string: */
/* End of include file zzabcorr.inc */
/* $ Brief_I/O */
/* Variable I/O Description */
/* -------- --- -------------------------------------------------- */
/* TRGSUB I Target body state subroutine. */
/* ET I Observer epoch. */
/* REF I Inertial reference frame of output state. */
/* ABCORR I Aberration correction flag. */
/* STOBS I State of the observer relative to the SSB. */
/* STARG O State of target. */
/* LT O One way light time between observer and target. */
/* DLT O Derivative of light time with respect to time. */
/* $ Detailed_Input */
/* TRGSUB is the name of an external subroutine that returns */
/* the geometric state of the target body relative to a */
/* center of motion, expressed in the inertial reference */
/* frame REF, at the epoch ET. */
/* The calling sequence of TRGSUB is */
/* SUBROUTINE TRGSUB ( ET, REF, TRGCTR, STATE ) */
/* DOUBLE PRECISION ET */
/* CHARACTER*(*) REF */
/* INTEGER TRGCTR */
/* DOUBLE PRECISION STATE ( 6 ) */
/* The inputs of TRGSUB are ET and REF; the outputs */
/* are TRGCTR and STATE. STATE is the geometric state */
/* of the target relative to the returned center of */
/* motion at ET, expressed in the frame REF. */
/* The target and observer define a state vector whose */
/* position component points from the observer to the */
/* target. */
/* ET is the ephemeris time, expressed as seconds past */
/* J2000 TDB, at which the state of the target body */
/* relative to the observer is to be computed. ET */
/* refers to time at the observer's location. */
/* REF is the inertial reference frame with respect to which */
/* the input state STOBS and the output state STARG are */
/* expressed. REF must be recognized by the SPICE */
/* Toolkit. The acceptable frames are listed in the */
/* Frames Required Reading, as well as in the SPICELIB */
/* routine CHGIRF. */
/* Case and blanks are not significant in the string */
/* REF. */
/* ABCORR indicates the aberration corrections to be applied to */
/* the state of the target body to account for one-way */
/* light time. See the discussion in the Particulars */
/* section for recommendations on how to choose */
/* aberration corrections. */
/* If ABCORR includes the stellar aberration correction */
/* symbol '+S', this flag is simply ignored. Aside from */
/* the possible presence of this symbol, ABCORR may be */
/* any of the following: */
/* 'NONE' Apply no correction. Return the */
/* geometric state of the target body */
/* relative to the observer. */
/* The following values of ABCORR apply to the */
/* "reception" case in which photons depart from the */
/* target's location at the light-time corrected epoch */
/* ET-LT and *arrive* at the observer's location at ET: */
/* 'LT' Correct for one-way light time (also */
/* called "planetary aberration") using a */
/* Newtonian formulation. This correction */
/* yields the state of the target at the */
/* moment it emitted photons arriving at */
/* the observer at ET. */
/* The light time correction involves */
/* iterative solution of the light time */
/* equation. (See the Particulars section */
/* of SPKEZR for details.) The solution */
/* invoked by the 'LT' option uses one */
/* iteration. */
/* 'CN' Converged Newtonian light time */
/* correction. In solving the light time */
/* equation, the 'CN' correction iterates */
/* until the solution converges (three */
/* iterations on all supported platforms). */
/* Whether the 'CN+S' solution is */
/* substantially more accurate than the */
/* 'LT' solution depends on the geometry */
/* of the participating objects and on the */
/* accuracy of the input data. In all */
/* cases this routine will execute more */
/* slowly when a converged solution is */
/* computed. See the Particulars section of */
/* SPKEZR for a discussion of precision of */
/* light time corrections. */
/* The following values of ABCORR apply to the */
/* "transmission" case in which photons *depart* from */
/* the observer's location at ET and arrive at the */
/* target's location at the light-time corrected epoch */
/* ET+LT: */
/* 'XLT' "Transmission" case: correct for */
/* one-way light time using a Newtonian */
/* formulation. This correction yields the */
/* state of the target at the moment it */
/* receives photons emitted from the */
/* observer's location at ET. */
/* 'XCN' "Transmission" case: converged */
/* Newtonian light time correction. */
/* Neither special nor general relativistic effects are */
/* accounted for in the aberration corrections applied */
/* by this routine. */
/* Case and blanks are not significant in the string */
/* ABCORR. */
/* STOBS is the geometric (uncorrected) state of the observer */
/* relative to the solar system barycenter at epoch ET. */
/* STOBS is a 6-vector: the first three components of */
/* STOBS represent a Cartesian position vector; the last */
/* three components represent the corresponding velocity */
/* vector. STOBS is expressed relative to the inertial */
/* reference frame designated by REF. */
/* Units are always km and km/sec. */
/* $ Detailed_Output */
/* STARG is a Cartesian state vector representing the position */
/* and velocity of the target body relative to the */
/* specified observer. STARG is corrected for the */
/* specified aberration, and is expressed with respect */
/* to the specified inertial reference frame. The first */
/* three components of STARG represent the x-, y- and */
/* z-components of the target's position; last three */
/* components form the corresponding velocity vector. */
/* The position component of STARG points from the */
/* observer's location at ET to the aberration-corrected */
/* location of the target. Note that the sense of the */
/* position vector is independent of the direction of */
/* radiation travel implied by the aberration */
/* correction. */
/* Units are always km and km/sec. */
/* LT is the one-way light time between the observer and */
/* target in seconds. If the target state is corrected */
/* for light time, then LT is the one-way light time */
/* between the observer and the light time-corrected */
/* target location. */
/* DLT is the derivative with respect to barycentric */
/* dynamical time of the one way light time between */
/* target and observer: */
/* DLT = d(LT)/d(ET) */
/* DLT can also be described as the rate of change of */
/* one way light time. DLT is unitless, since LT and */
/* ET both have units of TDB seconds. */
/* If the observer and target are at the same position, */
/* then DLT is set to zero. */
/* $ Parameters */
/* None. */
/* $ Exceptions */
/* 1) For the convenience of the caller, the input aberration */
/* correction flag can call for stellar aberration correction via */
/* inclusion of the '+S' suffix. This portion of the aberration */
/* correction flag is ignored if present. */
/* 2) If ABCORR calls for stellar aberration but not light */
/* time corrections, the error SPICE(NOTSUPPORTED) is */
/* signaled. */
/* 3) If ABCORR calls for relativistic light time corrections, the */
/* error SPICE(NOTSUPPORTED) is signaled. */
/* 4) If the value of ABCORR is not recognized, the error */
/* is diagnosed by a routine in the call tree of this */
/* routine. */
/* 5) If the reference frame requested is not a recognized */
/* inertial reference frame, the error SPICE(UNKNOWNFRAME) */
/* is signaled. */
/* 6) If the state of the target relative to the solar system */
/* barycenter cannot be computed, the error will be diagnosed */
/* by routines in the call tree of this routine. */
/* 7) If the observer and target are at the same position, */
/* then DLT is set to zero. This situation could arise, */
/* for example, when the observer is Mars and the target */
/* is the Mars barycenter. */
/* 8) If a division by zero error would occur in the computation */
/* of DLT, the error SPICE(DIVIDEBYZERO) is signaled. */
/* $ Files */
/* This routine computes states using SPK files that have been */
/* loaded into the SPICE system, normally via the kernel loading */
/* interface routine FURNSH. Application programs typically load */
/* kernels once before this routine is called, for example during */
/* program initialization; kernels need not be loaded repeatedly. */
/* See the routine FURNSH and the SPK and KERNEL Required Reading */
/* for further information on loading (and unloading) kernels. */
/* If any of the ephemeris data used to compute STARG are expressed */
/* relative to a non-inertial frame in the SPK files providing those */
/* data, additional kernels may be needed to enable the reference */
/* frame transformations required to compute the state. Normally */
/* these additional kernels are PCK files or frame kernels. Any */
/* such kernels must already be loaded at the time this routine is */
/* called. */
/* $ Particulars */
/* This routine supports higher-level routines that can */
/* perform both light time and stellar aberration corrections */
/* and that use target states provided by subroutines rather */
/* than by the conventional, public SPK APIs. For example, this */
/* routine can be used for objects having fixed positions */
/* on the surfaces of planets. */
/* $ Examples */
/* See usage in ZZSPKFAP. */
/* $ Restrictions */
/* 1) This routine must not be called by routines of the SPICE */
/* frame subsystem. It must not be called by any portion of */
/* the SPK subsystem other than the private SPK function-based */
/* component. */
/* 2) The input subroutine TRGSUB must not call this routine. */
/* or any of the supporting, private SPK routines */
/* 3) When possible, the routine SPKGEO should be used instead of */
/* this routine to compute geometric states. SPKGEO introduces */
/* less round-off error when the observer and target have common */
/* center that is closer to both objects than is the solar */
/* system barycenter. */
/* 4) Unlike most other SPK state computation routines, this */
/* routine requires that the output state be relative to an */
/* inertial reference frame. */
/* $ Literature_References */
/* None. */
/* $ Author_and_Institution */
/* N.J. Bachman (JPL) */
/* $ Version */
/* - SPICELIB Version 1.0.0, 04-JUL-2014 (NJB) */
/* Discussion of light time corrections was updated. Assertions */
/* that converged light time corrections are unlikely to be */
/* useful were removed. */
/* Last update was 22-FEB-2012 (NJB) */
/* -& */
/* $ Index_Entries */
/* low-level light time correction */
/* light-time corrected state from spk file */
/* get light-time corrected state */
/* -& */
/* $ Revisions */
/* None. */
/* -& */
/* SPICELIB functions */
/* Local parameters */
/* TOL is the tolerance used for a division-by-zero test */
/* performed prior to computation of DLT. */
/* Convergence limit: */
/* Maximum number of light time iterations for any */
/* aberration correction: */
/* Local variables */
/* Saved variables */
/* Initial values */
/* Standard SPICE error handling. */
if (return_()) {
return 0;
}
chkin_("ZZSPKFLT", (ftnlen)8);
if (pass1 || s_cmp(abcorr, prvcor, abcorr_len, (ftnlen)5) != 0) {
/* The aberration correction flag differs from the value it */
/* had on the previous call, if any. Analyze the new flag. */
zzvalcor_(abcorr, attblk, abcorr_len);
if (failed_()) {
chkout_("ZZSPKFLT", (ftnlen)8);
return 0;
}
/* The aberration correction flag is recognized; save it. */
s_copy(prvcor, abcorr, (ftnlen)5, abcorr_len);
/* Set logical flags indicating the attributes of the requested */
/* correction: */
/* XMIT is .TRUE. when the correction is for transmitted */
/* radiation. */
/* USELT is .TRUE. when any type of light time correction */
/* (normal or converged Newtonian) is specified. */
/* USECN indicates converged Newtonian light time correction. */
/* The above definitions are consistent with those used by */
/* ZZVALCOR. */
xmit = attblk[4];
uselt = attblk[1];
usecn = attblk[3];
usestl = attblk[2];
pass1 = FALSE_;
}
/* See if the reference frame is a recognized inertial frame. */
irfnum_(ref, &refid, ref_len);
if (refid == 0) {
setmsg_("The requested frame '#' is not a recognized inertial frame. "
, (ftnlen)60);
errch_("#", ref, (ftnlen)1, ref_len);
sigerr_("SPICE(UNKNOWNFRAME)", (ftnlen)19);
chkout_("ZZSPKFLT", (ftnlen)8);
return 0;
}
/* Find the geometric state of the target body with respect to */
/* the solar system barycenter. Subtract the state of the */
/* observer to get the relative state. Use this to compute the */
/* one-way light time. */
(*trgsub)(et, ref, &trgctr, sttctr, ref_len);
spkssb_(&trgctr, et, ref, ctrssb, ref_len);
if (failed_()) {
chkout_("ZZSPKFLT", (ftnlen)8);
return 0;
}
vaddg_(ctrssb, sttctr, &c__6, ssbtrg);
vsubg_(ssbtrg, stobs, &c__6, starg);
dist = vnorm_(starg);
*lt = dist / clight_();
if (*lt == 0.) {
/* This can happen only if the observer and target are at the */
/* same position. We don't consider this an error, but we're not */
/* going to compute the light time derivative. */
*dlt = 0.;
chkout_("ZZSPKFLT", (ftnlen)8);
return 0;
}
if (! uselt) {
/* This is a special case: we're not using light time */
/* corrections, so the derivative */
/* of light time is just */
/* (1/c) * d(VNORM(STARG))/dt */
*dlt = vdot_(starg, &starg[3]) / (dist * clight_());
/* LT and DLT are both set, so we can return. */
chkout_("ZZSPKFLT", (ftnlen)8);
return 0;
}
/* To correct for light time, find the state of the target body */
/* at the current epoch minus the one-way light time. Note that */
/* the observer remains where it is. */
/* Determine the sign of the light time offset. */
if (xmit) {
ltsign = 1;
} else {
ltsign = -1;
}
/* Let NUMITR be the number of iterations we'll perform to */
/* compute the light time. */
if (usecn) {
numitr = 5;
} else {
numitr = 1;
}
i__ = 0;
lterr = 1.;
while(i__ < numitr && lterr > 1e-17) {
/* LT was set either prior to this loop or */
/* during the previous loop iteration. */
d__1 = *et + ltsign * *lt;
epoch = touchd_(&d__1);
(*trgsub)(&epoch, ref, &trgctr, sttctr, ref_len);
spkssb_(&trgctr, &epoch, ref, ctrssb, ref_len);
if (failed_()) {
chkout_("ZZSPKFLT", (ftnlen)8);
return 0;
}
vaddg_(ctrssb, sttctr, &c__6, ssbtrg);
vsubg_(ssbtrg, stobs, &c__6, starg);
prvlt = *lt;
d__1 = vnorm_(starg) / clight_();
*lt = touchd_(&d__1);
/* LTERR is the magnitude of the change between the current */
/* estimate of light time and the previous estimate, relative to */
/* the previous light time corrected epoch. */
/* Computing MAX */
d__3 = 1., d__4 = abs(epoch);
d__2 = (d__1 = *lt - prvlt, abs(d__1)) / max(d__3,d__4);
lterr = touchd_(&d__2);
++i__;
}
/* At this point, STARG contains the light time corrected */
/* state of the target relative to the observer. */
/* Compute the derivative of light time with respect */
/* to time: dLT/dt. Below we derive the formula for */
/* this quantity for the reception case. Let */
/* POBS be the position of the observer relative to the */
/* solar system barycenter. */
/* VOBS be the velocity of the observer relative to the */
/* solar system barycenter. */
/* PTARG be the position of the target relative to the */
/* solar system barycenter. */
/* VTARG be the velocity of the target relative to the */
/* solar system barycenter. */
/* S be the sign of the light time correction. S is */
/* negative for the reception case. */
/* The light-time corrected position of the target relative to */
/* the observer at observation time ET, given the one-way */
/* light time LT is: */
/* PTARG(ET+S*LT) - POBS(ET) */
/* The light-time corrected velocity of the target relative to */
/* the observer at observation time ET is */
/* VTARG(ET+S*LT)*( 1 + S*d(LT)/d(ET) ) - VOBS(ET) */
/* We need to compute dLT/dt. Below, we use the facts that, */
/* for a time-dependent vector X(t), */
/* ||X|| = <X,X> ** (1/2) */
/* d(||X||)/dt = (1/2)<X,X>**(-1/2) * 2 * <X,dX/dt> */
/* = <X,X>**(-1/2) * <X,dX/dt> */
/* = <X,dX/dt> / ||X|| */
/* Newtonian light time equation: */
/* LT = (1/c) * || PTARG(ET+S*LT) - POBS(ET)|| */
/* Differentiate both sides: */
/* dLT/dt = (1/c) * ( 1 / || PTARG(ET+S*LT) - POBS(ET) || ) */
/* * < PTARG(ET+S*LT) - POBS(ET), */
/* VTARG(ET+S*LT)*(1+S*d(LT)/d(ET)) - VOBS(ET) > */
/* = (1/c) * ( 1 / || PTARG(ET+S*LT) - POBS(ET) || ) */
/* * ( < PTARG(ET+S*LT) - POBS(ET), */
/* VTARG(ET+S*LT) - VOBS(ET) > */
/* + < PTARG(ET+S*LT) - POBS(ET), */
/* VTARG(ET+S*LT) > * (S*d(LT)/d(ET)) ) */
/* Let */
/* A = (1/c) * ( 1 / || PTARG(ET+S*LT) - POBS(ET) || ) */
/* B = < PTARG(ET+S*LT) - POBS(ET), VTARG(ET+S*LT) - VOBS(ET) > */
/* C = < PTARG(ET+S*LT) - POBS(ET), VTARG(ET+S*LT) > */
/* Then */
/* d(LT)/d(ET) = A * ( B + C * S*d(LT)/d(ET) ) */
/* which implies */
/* d(LT)/d(ET) = A*B / ( 1 - S*C*A ) */
a = 1. / (clight_() * vnorm_(starg));
b = vdot_(starg, &starg[3]);
c__ = vdot_(starg, &ssbtrg[3]);
/* For physically realistic target velocities, S*C*A cannot equal 1. */
/* We'll check for this case anyway. */
if (ltsign * c__ * a > .99999999989999999) {
setmsg_("Target range rate magnitude is approximately the speed of l"
"ight. The light time derivative cannot be computed.", (ftnlen)
110);
sigerr_("SPICE(DIVIDEBYZERO)", (ftnlen)19);
chkout_("ZZSPKFLT", (ftnlen)8);
return 0;
}
/* Compute DLT: the rate of change of light time. */
*dlt = a * b / (1. - ltsign * c__ * a);
/* Overwrite the velocity portion of the output state */
/* with the light-time corrected velocity. */
d__1 = ltsign * *dlt + 1.;
vlcom_(&d__1, &ssbtrg[3], &c_b19, &stobs[3], &starg[3]);
chkout_("ZZSPKFLT", (ftnlen)8);
return 0;
} /* zzspkflt_ */
/* $Procedure SPKLTC ( S/P Kernel, light time corrected state ) */
/* Subroutine */ int spkltc_(integer *targ, doublereal *et, char *ref, char *
abcorr, doublereal *stobs, doublereal *starg, doublereal *lt,
doublereal *dlt, ftnlen ref_len, ftnlen abcorr_len)
{
/* Initialized data */
static logical pass1 = TRUE_;
static char prvcor[5] = " ";
/* System generated locals */
doublereal d__1, d__2, d__3, d__4;
/* Builtin functions */
integer s_cmp(char *, char *, ftnlen, ftnlen);
/* Subroutine */ int s_copy(char *, char *, ftnlen, ftnlen);
/* Local variables */
doublereal dist;
extern doublereal vdot_(doublereal *, doublereal *);
static logical xmit;
extern /* Subroutine */ int zzvalcor_(char *, logical *, ftnlen);
doublereal a, b, c__;
integer i__, refid;
extern /* Subroutine */ int chkin_(char *, ftnlen);
doublereal epoch;
extern /* Subroutine */ int errch_(char *, char *, ftnlen, ftnlen);
static logical usecn;
extern /* Subroutine */ int vlcom_(doublereal *, doublereal *, doublereal
*, doublereal *, doublereal *), vsubg_(doublereal *, doublereal *,
integer *, doublereal *);
doublereal ssblt, lterr;
static logical uselt;
extern doublereal vnorm_(doublereal *);
doublereal prvlt;
extern logical failed_(void);
extern doublereal clight_(void);
logical attblk[15];
extern doublereal touchd_(doublereal *);
extern /* Subroutine */ int spkgeo_(integer *, doublereal *, char *,
integer *, doublereal *, doublereal *, ftnlen), sigerr_(char *,
ftnlen), chkout_(char *, ftnlen);
integer ltsign;
extern /* Subroutine */ int irfnum_(char *, integer *, ftnlen), setmsg_(
char *, ftnlen);
doublereal ssbtrg[6];
integer numitr;
extern logical return_(void);
logical usestl;
/* $ Abstract */
/* Return the state (position and velocity) of a target body */
/* relative to an observer, optionally corrected for light time, */
/* expressed relative to an inertial reference frame. */
/* $ 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 */
/* SPK */
/* $ Keywords */
/* EPHEMERIS */
/* $ Declarations */
/* $ Abstract */
/* Include file zzabcorr.inc */
/* SPICE private file intended solely for the support of SPICE */
/* routines. Users should not include this file directly due */
/* to the volatile nature of this file */
/* The parameters below define the structure of an aberration */
/* correction attribute block. */
/* $ 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. */
/* $ Parameters */
/* An aberration correction attribute block is an array of logical */
/* flags indicating the attributes of the aberration correction */
/* specified by an aberration correction string. The attributes */
/* are: */
/* - Is the correction "geometric"? */
/* - Is light time correction indicated? */
/* - Is stellar aberration correction indicated? */
/* - Is the light time correction of the "converged */
/* Newtonian" variety? */
/* - Is the correction for the transmission case? */
/* - Is the correction relativistic? */
/* The parameters defining the structure of the block are as */
/* follows: */
/* NABCOR Number of aberration correction choices. */
/* ABATSZ Number of elements in the aberration correction */
/* block. */
/* GEOIDX Index in block of geometric correction flag. */
/* LTIDX Index of light time flag. */
/* STLIDX Index of stellar aberration flag. */
/* CNVIDX Index of converged Newtonian flag. */
/* XMTIDX Index of transmission flag. */
/* RELIDX Index of relativistic flag. */
/* The following parameter is not required to define the block */
/* structure, but it is convenient to include it here: */
/* CORLEN The maximum string length required by any aberration */
/* correction string */
/* $ Author_and_Institution */
/* N.J. Bachman (JPL) */
/* $ Literature_References */
/* None. */
/* $ Version */
/* - SPICELIB Version 1.0.0, 18-DEC-2004 (NJB) */
/* -& */
/* Number of aberration correction choices: */
/* Aberration correction attribute block size */
/* (number of aberration correction attributes): */
/* Indices of attributes within an aberration correction */
/* attribute block: */
/* Maximum length of an aberration correction string: */
/* End of include file zzabcorr.inc */
/* $ Brief_I/O */
/* Variable I/O Description */
/* -------- --- -------------------------------------------------- */
/* TARG I Target body. */
/* ET I Observer epoch. */
/* REF I Inertial reference frame of output state. */
/* ABCORR I Aberration correction flag. */
/* STOBS I State of the observer relative to the SSB. */
/* STARG O State of target. */
/* LT O One way light time between observer and target. */
/* DLT O Derivative of light time with respect to time. */
/* $ Detailed_Input */
/* TARG is the NAIF ID code for a target body. The target */
/* and observer define a state vector whose position */
/* component points from the observer to the target. */
/* ET is the ephemeris time, expressed as seconds past */
/* J2000 TDB, at which the state of the target body */
/* relative to the observer is to be computed. ET */
/* refers to time at the observer's location. */
/* REF is the inertial reference frame with respect to which */
/* the input state STOBS and the output state STARG are */
/* expressed. REF must be recognized by the SPICE */
/* Toolkit. The acceptable frames are listed in the */
/* Frames Required Reading, as well as in the SPICELIB */
/* routine CHGIRF. */
/* Case and blanks are not significant in the string */
/* REF. */
/* ABCORR indicates the aberration corrections to be applied to */
/* the state of the target body to account for one-way */
/* light time. See the discussion in the Particulars */
/* section for recommendations on how to choose */
/* aberration corrections. */
/* If ABCORR includes the stellar aberration correction */
/* symbol '+S', this flag is simply ignored. Aside from */
/* the possible presence of this symbol, ABCORR may be */
/* any of the following: */
/* 'NONE' Apply no correction. Return the */
/* geometric state of the target body */
/* relative to the observer. */
/* The following values of ABCORR apply to the */
/* "reception" case in which photons depart from the */
/* target's location at the light-time corrected epoch */
/* ET-LT and *arrive* at the observer's location at ET: */
/* 'LT' Correct for one-way light time (also */
/* called "planetary aberration") using a */
/* Newtonian formulation. This correction */
/* yields the state of the target at the */
/* moment it emitted photons arriving at */
/* the observer at ET. */
/* The light time correction involves */
/* iterative solution of the light time */
/* equation (see Particulars for details). */
/* The solution invoked by the 'LT' option */
/* uses one iteration. */
/* 'CN' Converged Newtonian light time */
/* correction. In solving the light time */
/* equation, the 'CN' correction iterates */
/* until the solution converges (three */
/* iterations on all supported platforms). */
/* Whether the 'CN+S' solution is */
/* substantially more accurate than the */
/* 'LT' solution depends on the geometry */
/* of the participating objects and on the */
/* accuracy of the input data. In all */
/* cases this routine will execute more */
/* slowly when a converged solution is */
/* computed. See the Particulars section of */
/* SPKEZR for a discussion of precision of */
/* light time corrections. */
/* The following values of ABCORR apply to the */
/* "transmission" case in which photons *depart* from */
/* the observer's location at ET and arrive at the */
/* target's location at the light-time corrected epoch */
/* ET+LT: */
/* 'XLT' "Transmission" case: correct for */
/* one-way light time using a Newtonian */
/* formulation. This correction yields the */
/* state of the target at the moment it */
/* receives photons emitted from the */
/* observer's location at ET. */
/* 'XCN' "Transmission" case: converged */
/* Newtonian light time correction. */
/* Neither special nor general relativistic effects are */
/* accounted for in the aberration corrections applied */
/* by this routine. */
/* Case and blanks are not significant in the string */
/* ABCORR. */
/* STOBS is the geometric (uncorrected) state of the observer */
/* relative to the solar system barycenter at epoch ET. */
/* STOBS is a 6-vector: the first three components of */
/* STOBS represent a Cartesian position vector; the last */
/* three components represent the corresponding velocity */
/* vector. STOBS is expressed relative to the inertial */
/* reference frame designated by REF. */
/* Units are always km and km/sec. */
/* $ Detailed_Output */
/* STARG is a Cartesian state vector representing the position */
/* and velocity of the target body relative to the */
/* specified observer. STARG is corrected for the */
/* specified aberration, and is expressed with respect */
/* to the specified inertial reference frame. The first */
/* three components of STARG represent the x-, y- and */
/* z-components of the target's position; last three */
/* components form the corresponding velocity vector. */
/* The position component of STARG points from the */
/* observer's location at ET to the aberration-corrected */
/* location of the target. Note that the sense of the */
/* position vector is independent of the direction of */
/* radiation travel implied by the aberration */
/* correction. */
/* Units are always km and km/sec. */
/* LT is the one-way light time between the observer and */
/* target in seconds. If the target state is corrected */
/* for light time, then LT is the one-way light time */
/* between the observer and the light time-corrected */
/* target location. */
/* DLT is the derivative with respect to barycentric */
/* dynamical time of the one way light time between */
/* target and observer: */
/* DLT = d(LT)/d(ET) */
/* DLT can also be described as the rate of change of */
/* one way light time. DLT is unitless, since LT and */
/* ET both have units of TDB seconds. */
/* If the observer and target are at the same position, */
/* then DLT is set to zero. */
/* $ Parameters */
/* None. */
/* $ Exceptions */
/* 1) For the convenience of the caller, the input aberration */
/* correction flag can call for stellar aberration correction via */
/* inclusion of the '+S' suffix. This portion of the aberration */
/* correction flag is ignored if present. */
/* 2) If the value of ABCORR is not recognized, the error */
/* is diagnosed by a routine in the call tree of this */
/* routine. */
/* 3) If the reference frame requested is not a recognized */
/* inertial reference frame, the error SPICE(BADFRAME) */
/* is signaled. */
/* 4) If the state of the target relative to the solar system */
/* barycenter cannot be computed, the error will be diagnosed */
/* by routines in the call tree of this routine. */
/* 5) If the observer and target are at the same position, */
/* then DLT is set to zero. This situation could arise, */
/* for example, when the observer is Mars and the target */
/* is the Mars barycenter. */
/* 6) If a division by zero error would occur in the computation */
/* of DLT, the error SPICE(DIVIDEBYZERO) is signaled. */
/* $ Files */
/* This routine computes states using SPK files that have been */
/* loaded into the SPICE system, normally via the kernel loading */
/* interface routine FURNSH. Application programs typically load */
/* kernels once before this routine is called, for example during */
/* program initialization; kernels need not be loaded repeatedly. */
/* See the routine FURNSH and the SPK and KERNEL Required Reading */
/* for further information on loading (and unloading) kernels. */
/* If any of the ephemeris data used to compute STARG are expressed */
/* relative to a non-inertial frame in the SPK files providing those */
/* data, additional kernels may be needed to enable the reference */
/* frame transformations required to compute the state. Normally */
/* these additional kernels are PCK files or frame kernels. Any */
/* such kernels must already be loaded at the time this routine is */
/* called. */
/* $ Particulars */
/* This routine supports higher-level SPK API routines that can */
/* perform both light time and stellar aberration corrections. */
/* User applications normally will not need to call this routine */
/* directly. */
/* See the header of the routine SPKEZR for a detailed discussion */
/* of aberration corrections. */
/* $ 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. */
/* 1) Look up a sequence of states of the Moon as seen from the */
/* Earth. Use light time corrections. Compute the first state for */
/* the epoch 2000 JAN 1 12:00:00 TDB; compute subsequent states at */
/* intervals of 1 hour. For each epoch, display the states, the */
/* one way light time between target and observer, and the rate of */
/* change of the one way light time. */
/* Use the following meta-kernel to specify the kernels to */
/* load: */
/* KPL/MK */
/* File name: spkltc.tm */
/* This meta-kernel is intended to support operation of SPICE */
/* example programs. The kernels shown here should not be */
/* assumed to contain adequate or correct versions of data */
/* required by SPICE-based user applications. */
/* In order for an application to use this meta-kernel, the */
/* kernels referenced here must be present in the user's */
/* current working directory. */
/* \begindata */
/* KERNELS_TO_LOAD = ( 'de421.bsp', */
/* 'pck00010.tpc', */
/* 'naif0010.tls' ) */
/* \begintext */
/* The code example follows: */
/* PROGRAM EX1 */
/* IMPLICIT NONE */
/* C */
/* C Local constants */
/* C */
/* C The meta-kernel name shown here refers to a file whose */
/* C contents are those shown above. This file and the kernels */
/* C it references must exist in your current working directory. */
/* C */
/* CHARACTER*(*) META */
/* PARAMETER ( META = 'spkltc.tm' ) */
/* C */
/* C Use a time step of 1 hour; look up 5 states. */
/* C */
/* DOUBLE PRECISION STEP */
/* PARAMETER ( STEP = 3600.0D0 ) */
/* INTEGER MAXITR */
/* PARAMETER ( MAXITR = 5 ) */
/* C */
/* C Local variables */
/* C */
/* DOUBLE PRECISION DLT */
/* DOUBLE PRECISION ET */
/* DOUBLE PRECISION ET0 */
/* DOUBLE PRECISION LT */
/* DOUBLE PRECISION STATE ( 6 ) */
/* DOUBLE PRECISION STOBS ( 6 ) */
/* INTEGER I */
/* C */
/* C Load the SPK and LSK kernels via the meta-kernel. */
/* C */
/* CALL FURNSH ( META ) */
/* C */
/* C Convert the start time to seconds past J2000 TDB. */
/* C */
/* CALL STR2ET ( '2000 JAN 1 12:00:00 TDB', ET0 ) */
/* C */
/* C Step through a series of epochs, looking up a */
/* C state vector at each one. */
/* C */
/* DO I = 1, MAXITR */
/* ET = ET0 + (I-1)*STEP */
/* C */
/* C Look up a state vector at epoch ET using the */
/* C following inputs: */
/* C */
/* C Target: Moon (NAIF ID code 301) */
/* C Reference frame: J2000 */
/* C Aberration correction: Light time ('LT') */
/* C Observer: Earth (NAIF ID code 399) */
/* C */
/* C Before we can execute this computation, we'll need the */
/* C geometric state of the observer relative to the solar */
/* C system barycenter at ET, expressed relative to the */
/* C J2000 reference frame: */
/* C */
/* CALL SPKSSB ( 399, ET, 'J2000', STOBS ) */
/* C */
/* C Now compute the desired state vector: */
/* C */
/* CALL SPKLTC ( 301, ET, 'J2000', 'LT', */
/* . STOBS, STATE, LT, DLT ) */
/* WRITE (*,*) 'ET = ', ET */
/* WRITE (*,*) 'J2000 x-position (km): ', STATE(1) */
/* WRITE (*,*) 'J2000 y-position (km): ', STATE(2) */
/* WRITE (*,*) 'J2000 z-position (km): ', STATE(3) */
/* WRITE (*,*) 'J2000 x-velocity (km/s): ', STATE(4) */
/* WRITE (*,*) 'J2000 y-velocity (km/s): ', STATE(5) */
/* WRITE (*,*) 'J2000 z-velocity (km/s): ', STATE(6) */
/* WRITE (*,*) 'One-way light time (s): ', LT */
/* WRITE (*,*) 'Light time rate: ', DLT */
/* WRITE (*,*) ' ' */
/* END DO */
/* END */
/* On a PC/Linux/gfortran platform, the following output was */
/* produced: */
/* ET = 0.0000000000000000 */
/* J2000 x-position (km): -291569.26541282982 */
/* J2000 y-position (km): -266709.18647825718 */
/* J2000 z-position (km): -76099.155118763447 */
/* J2000 x-velocity (km/s): 0.64353061322177041 */
/* J2000 y-velocity (km/s): -0.66608181700820079 */
/* J2000 z-velocity (km/s): -0.30132283179625752 */
/* One-way light time (s): 1.3423106103251679 */
/* Light time rate: 1.07316908698977495E-007 */
/* ET = 3600.0000000000000 */
/* J2000 x-position (km): -289240.78128184378 */
/* J2000 y-position (km): -269096.44087958336 */
/* J2000 z-position (km): -77180.899725757539 */
/* J2000 x-velocity (km/s): 0.65006211520087476 */
/* J2000 y-velocity (km/s): -0.66016273921695667 */
/* J2000 z-velocity (km/s): -0.29964267390571342 */
/* One-way light time (s): 1.3426939548635302 */
/* Light time rate: 1.05652598952224259E-007 */
/* ET = 7200.0000000000000 */
/* J2000 x-position (km): -286888.88736709207 */
/* J2000 y-position (km): -271462.30170547962 */
/* J2000 z-position (km): -78256.555682137609 */
/* J2000 x-velocity (km/s): 0.65653599154284592 */
/* J2000 y-velocity (km/s): -0.65419657680401588 */
/* J2000 z-velocity (km/s): -0.29794027307420823 */
/* One-way light time (s): 1.3430713117337547 */
/* Light time rate: 1.03990456898758609E-007 */
/* ET = 10800.000000000000 */
/* J2000 x-position (km): -284513.79173691198 */
/* J2000 y-position (km): -273806.60031034052 */
/* J2000 z-position (km): -79326.043183274567 */
/* J2000 x-velocity (km/s): 0.66295190054599118 */
/* J2000 y-velocity (km/s): -0.64818380709706158 */
/* J2000 z-velocity (km/s): -0.29621577937090349 */
/* One-way light time (s): 1.3434426890693671 */
/* Light time rate: 1.02330665243423737E-007 */
/* ET = 14400.000000000000 */
/* J2000 x-position (km): -282115.70368389413 */
/* J2000 y-position (km): -276129.16976799071 */
/* J2000 z-position (km): -80389.282965712249 */
/* J2000 x-velocity (km/s): 0.66930950377548726 */
/* J2000 y-velocity (km/s): -0.64212490805688027 */
/* J2000 z-velocity (km/s): -0.29446934336246899 */
/* One-way light time (s): 1.3438080956559786 */
/* Light time rate: 1.00673403630050830E-007 */
/* $ Restrictions */
/* 1) The routine SPKGEO should be used instead of this routine */
/* to compute geometric states. SPKGEO introduces less */
/* round-off error when the observer and target have common */
/* center that is closer to both objects than is the solar */
/* system barycenter. */
/* 2) The kernel files to be used by SPKLTC must be loaded */
/* (normally by the SPICELIB kernel loader FURNSH) before */
/* this routine is called. */
/* 3) Unlike most other SPK state computation routines, this */
/* routine requires that the output state be relative to an */
/* inertial reference frame. */
/* $ Literature_References */
/* None. */
/* $ Author_and_Institution */
/* N.J. Bachman (JPL) */
/* $ Version */
/* - SPICELIB Version 2.0.0, 04-JUL-2014 (NJB) */
/* Discussion of light time corrections was updated. Assertions */
/* that converged light time corrections are unlikely to be */
/* useful were removed. */
/* Last update was 02-MAY-2012 (NJB) */
/* Updated to ensure convergence when CN or XCN light time */
/* corrections are used. The new algorithm also terminates early */
/* (after fewer than three iterations) when convergence is */
/* attained. */
/* Call to ZZPRSCOR was replaced by a call to ZZVALCOR. */
/* - SPICELIB Version 1.0.0, 11-JAN-2008 (NJB) */
/* -& */
/* $ Index_Entries */
/* low-level light time correction */
/* light-time corrected state from spk file */
/* get light-time corrected state */
/* -& */
/* $ Revisions */
/* None. */
/* -& */
/* SPICELIB functions */
/* Local parameters */
/* TOL is the tolerance used for a division-by-zero test */
/* performed prior to computation of DLT. */
/* Convergence limit: */
/* Maximum number of light time iterations for any */
/* aberration correction: */
/* Local variables */
/* Saved variables */
/* Initial values */
/* Standard SPICE error handling. */
if (return_()) {
return 0;
} else {
chkin_("SPKLTC", (ftnlen)6);
}
if (pass1 || s_cmp(abcorr, prvcor, abcorr_len, (ftnlen)5) != 0) {
/* The aberration correction flag differs from the value it */
/* had on the previous call, if any. Analyze the new flag. */
zzvalcor_(abcorr, attblk, abcorr_len);
if (failed_()) {
chkout_("SPKLTC", (ftnlen)6);
return 0;
}
/* The aberration correction flag is recognized; save it. */
s_copy(prvcor, abcorr, (ftnlen)5, abcorr_len);
/* Set logical flags indicating the attributes of the requested */
/* correction: */
/* XMIT is .TRUE. when the correction is for transmitted */
/* radiation. */
/* USELT is .TRUE. when any type of light time correction */
/* (normal or converged Newtonian) is specified. */
/* USECN indicates converged Newtonian light time correction. */
/* The above definitions are consistent with those used by */
/* ZZVALCOR. */
xmit = attblk[4];
uselt = attblk[1];
usecn = attblk[3];
usestl = attblk[2];
pass1 = FALSE_;
}
/* See if the reference frame is a recognized inertial frame. */
irfnum_(ref, &refid, ref_len);
if (refid == 0) {
setmsg_("The requested frame '#' is not a recognized inertial frame. "
, (ftnlen)60);
errch_("#", ref, (ftnlen)1, ref_len);
sigerr_("SPICE(BADFRAME)", (ftnlen)15);
chkout_("SPKLTC", (ftnlen)6);
return 0;
}
/* Find the geometric state of the target body with respect to */
/* the solar system barycenter. Subtract the state of the */
/* observer to get the relative state. Use this to compute the */
/* one-way light time. */
spkgeo_(targ, et, ref, &c__0, ssbtrg, &ssblt, ref_len);
if (failed_()) {
chkout_("SPKLTC", (ftnlen)6);
return 0;
}
vsubg_(ssbtrg, stobs, &c__6, starg);
dist = vnorm_(starg);
*lt = dist / clight_();
if (*lt == 0.) {
/* This can happen only if the observer and target are at the */
/* same position. We don't consider this an error, but we're not */
/* going to compute the light time derivative. */
*dlt = 0.;
chkout_("SPKLTC", (ftnlen)6);
return 0;
}
if (! uselt) {
/* This is a special case: we're not using light time */
/* corrections, so the derivative */
/* of light time is just */
/* (1/c) * d(VNORM(STARG))/dt */
*dlt = vdot_(starg, &starg[3]) / (dist * clight_());
/* LT and DLT are both set, so we can return. */
chkout_("SPKLTC", (ftnlen)6);
return 0;
}
/* To correct for light time, find the state of the target body */
/* at the current epoch minus the one-way light time. Note that */
/* the observer remains where it is. */
/* Determine the sign of the light time offset. */
if (xmit) {
ltsign = 1;
} else {
ltsign = -1;
}
/* Let NUMITR be the number of iterations we'll perform to */
/* compute the light time. */
if (usecn) {
numitr = 5;
} else {
numitr = 1;
}
i__ = 0;
lterr = 1.;
while(i__ < numitr && lterr > 1e-17) {
/* LT was set either prior to this loop or */
/* during the previous loop iteration. */
epoch = *et + ltsign * *lt;
spkgeo_(targ, &epoch, ref, &c__0, ssbtrg, &ssblt, ref_len);
if (failed_()) {
chkout_("SPKLTC", (ftnlen)6);
return 0;
}
vsubg_(ssbtrg, stobs, &c__6, starg);
prvlt = *lt;
d__1 = vnorm_(starg) / clight_();
*lt = touchd_(&d__1);
/* LTERR is the magnitude of the change between the current */
/* estimate of light time and the previous estimate, relative to */
/* the previous light time corrected epoch. */
/* Computing MAX */
d__3 = 1., d__4 = abs(epoch);
d__2 = (d__1 = *lt - prvlt, abs(d__1)) / max(d__3,d__4);
lterr = touchd_(&d__2);
++i__;
}
/* At this point, STARG contains the light time corrected */
/* state of the target relative to the observer. */
/* Compute the derivative of light time with respect */
/* to time: dLT/dt. Below we derive the formula for */
/* this quantity for the reception case. Let */
/* POBS be the position of the observer relative to the */
/* solar system barycenter. */
/* VOBS be the velocity of the observer relative to the */
/* solar system barycenter. */
/* PTARG be the position of the target relative to the */
/* solar system barycenter. */
/* VTARG be the velocity of the target relative to the */
/* solar system barycenter. */
/* S be the sign of the light time correction. S is */
/* negative for the reception case. */
/* The light-time corrected position of the target relative to */
/* the observer at observation time ET, given the one-way */
/* light time LT is: */
/* PTARG(ET+S*LT) - POBS(ET) */
/* The light-time corrected velocity of the target relative to */
/* the observer at observation time ET is */
/* VTARG(ET+S*LT)*( 1 + S*d(LT)/d(ET) ) - VOBS(ET) */
/* We need to compute dLT/dt. Below, we use the facts that, */
/* for a time-dependent vector X(t), */
/* ||X|| = <X,X> ** (1/2) */
/* d(||X||)/dt = (1/2)<X,X>**(-1/2) * 2 * <X,dX/dt> */
/* = <X,X>**(-1/2) * <X,dX/dt> */
/* = <X,dX/dt> / ||X|| */
/* Newtonian light time equation: */
/* LT = (1/c) * || PTARG(ET+S*LT) - POBS(ET)|| */
/* Differentiate both sides: */
/* dLT/dt = (1/c) * ( 1 / || PTARG(ET+S*LT) - POBS(ET) || ) */
/* * < PTARG(ET+S*LT) - POBS(ET), */
/* VTARG(ET+S*LT)*(1+S*d(LT)/d(ET)) - VOBS(ET) > */
/* = (1/c) * ( 1 / || PTARG(ET+S*LT) - POBS(ET) || ) */
/* * ( < PTARG(ET+S*LT) - POBS(ET), */
/* VTARG(ET+S*LT) - VOBS(ET) > */
/* + < PTARG(ET+S*LT) - POBS(ET), */
/* VTARG(ET+S*LT) > * (S*d(LT)/d(ET)) ) */
/* Let */
/* A = (1/c) * ( 1 / || PTARG(ET+S*LT) - POBS(ET) || ) */
/* B = < PTARG(ET+S*LT) - POBS(ET), VTARG(ET+S*LT) - VOBS(ET) > */
/* C = < PTARG(ET+S*LT) - POBS(ET), VTARG(ET+S*LT) > */
/* Then */
/* d(LT)/d(ET) = A * ( B + C * S*d(LT)/d(ET) ) */
/* which implies */
/* d(LT)/d(ET) = A*B / ( 1 - S*C*A ) */
a = 1. / (clight_() * vnorm_(starg));
b = vdot_(starg, &starg[3]);
c__ = vdot_(starg, &ssbtrg[3]);
/* For physically realistic target velocities, S*C*A cannot equal 1. */
/* We'll check for this case anyway. */
if (ltsign * c__ * a > .99999999989999999) {
setmsg_("Target range rate magnitude is approximately the speed of l"
"ight. The light time derivative cannot be computed.", (ftnlen)
110);
sigerr_("SPICE(DIVIDEBYZERO)", (ftnlen)19);
chkout_("SPKLTC", (ftnlen)6);
return 0;
}
/* Compute DLT: the rate of change of light time. */
*dlt = a * b / (1. - ltsign * c__ * a);
/* Overwrite the velocity portion of the output state */
/* with the light-time corrected velocity. */
d__1 = ltsign * *dlt + 1.;
vlcom_(&d__1, &ssbtrg[3], &c_b19, &stobs[3], &starg[3]);
chkout_("SPKLTC", (ftnlen)6);
return 0;
} /* spkltc_ */
