/* illum.f -- translated by f2c (version 19980913).
   You must link the resulting object file with the libraries:
	-lf2c -lm   (in that order)
*/

#include "f2c.h"

/* Table of constant values */

static integer c__10 = 10;
static integer c__3 = 3;

/* $Procedure ILLUM ( Illumination angles ) */
/* Subroutine */ int illum_(char *target, doublereal *et, char *abcorr, char *
	obsrvr, doublereal *spoint, doublereal *phase, doublereal *solar, 
	doublereal *emissn, ftnlen target_len, ftnlen abcorr_len, ftnlen 
	obsrvr_len)
{
    extern doublereal vsep_(doublereal *, doublereal *);
    extern /* Subroutine */ int vsub_(doublereal *, doublereal *, doublereal *
	    ), vequ_(doublereal *, doublereal *);
    integer n;
    doublereal radii[3];
    extern /* Subroutine */ int chkin_(char *, ftnlen), errch_(char *, char *,
	     ftnlen, ftnlen);
    logical found;
    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);
    char frname[80];
    integer trgcde;
    doublereal offobs[3], obsvec[3], tepoch, normal[3];
    extern /* Subroutine */ int sigerr_(char *, ftnlen), chkout_(char *, 
	    ftnlen);
    doublereal offsun[3];
    extern /* Subroutine */ int setmsg_(char *, ftnlen);
    doublereal sstate[6], sunvec[3], tstate[6];
    extern /* Subroutine */ int surfnm_(doublereal *, doublereal *, 
	    doublereal *, doublereal *, doublereal *);
    extern logical return_(void);
    extern /* Subroutine */ int vminus_(doublereal *, doublereal *);
    doublereal lts;

/* $ Abstract */

/*     Deprecated: This routine has been superseded by the SPICELIB */
/*     routine ILUMIN. This routine is supported for purposes of */
/*     backward compatibility only. */

/*     Find the illumination angles at a specified surface point of a */
/*     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 */

/*     KERNEL */
/*     NAIF_IDS */
/*     SPK */
/*     TIME */

/* $ Keywords */

/*     GEOMETRY */
/*     MOSPICE */

/* $ Declarations */
/* $ Brief_I/O */

/*     Variable  I/O  Description */
/*     --------  ---  -------------------------------------------------- */
/*     TARGET     I   Name of target body. */
/*     ET         I   Epoch in ephemeris seconds past J2000. */
/*     ABCORR     I   Desired aberration correction. */
/*     OBSRVR     I   Name of observing body. */
/*     SPOINT     I   Body-fixed coordinates of a target surface point. */
/*     PHASE      O   Phase angle at the surface point. */
/*     SOLAR      O   Solar incidence angle at the surface point. */
/*     EMISSN     O   Emission angle at the surface point. */

/* $ Detailed_Input */

/*     TARGET         is the name of the target body.  TARGET is */
/*                    case-insensitive, and leading and trailing blanks */
/*                    in TARGET are not significant. Optionally, you may */
/*                    supply a string containing the integer ID code for */
/*                    the object.  For example both 'MOON' and '301' are */
/*                    legitimate strings that indicate the moon is the */
/*                    target body. */

/*     ET             is the epoch, specified in ephemeris seconds past */
/*                    J2000, at which the apparent illumination angles at */
/*                    the specified surface point on the target body, as */
/*                    seen from the observing body, are to be computed. */

/*     ABCORR         is the aberration correction to be used in */
/*                    computing the location and orientation of the */
/*                    target body and the location of the Sun.  Possible */
/*                    values are: */

/*                       'NONE'        No aberration correction. */

/*                       'LT'          Correct the position and */
/*                                     orientation of target body for */
/*                                     light time, and correct the */
/*                                     position of the Sun for light */
/*                                     time. */

/*                       'LT+S'        Correct the observer-target vector */
/*                                     for light time and stellar */
/*                                     aberration, correct the */
/*                                     orientation of the target body */
/*                                     for light time, and correct the */
/*                                     target-Sun vector for light time */
/*                                     and stellar aberration. */

/*                          '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, typically a */
/*                    spacecraft, the earth, or a surface point on the */
/*                    earth.  OBSRVR is case-insensitive, and leading */
/*                    and trailing blanks in OBSRVR are not significant. */
/*                    Optionally, you may supply a string containing the */
/*                    integer ID code for the object.  For example both */
/*                    'EARTH' and '399' are legitimate strings that */
/*                    indicate the earth is the observer. */

/*                    OBSRVR may be not be identical to TARGET. */

/*     SPOINT         is a surface point on the target body, expressed */
/*                    in rectangular body-fixed (body equator and prime */
/*                    meridian) coordinates.  SPOINT need not be visible */
/*                    from the observer's location at time ET. */

/* $ Detailed_Output */


/*     PHASE          is the phase angle at SPOINT, as seen from OBSRVR */
/*                    at time ET.  This is the angle between the */
/*                    SPOINT-OBSRVR vector and the SPOINT-Sun vector. */
/*                    Units are radians.  The range of  PHASE is [0, pi]. */
/*                    See Particulars below for a detailed discussion of */
/*                    the definition. */

/*     SOLAR          is the solar incidence angle at SPOINT, as seen */
/*                    from OBSRVR at time ET.  This is the angle */
/*                    between the surface normal vector at SPOINT and the */
/*                    SPOINT-Sun vector.  Units are radians.  The range */
/*                    of SOLAR is [0, pi]. See Particulars below for a */
/*                    detailed discussion of the definition. */

/*     EMISSN         is the emission angle at SPOINT, as seen from */
/*                    OBSRVR at time ET.  This is the angle between the */
/*                    surface normal vector at SPOINT and the */
/*                    SPOINT-observer vector.  Units are radians.  The */
/*                    range of EMISSN is [0, pi]. See Particulars below */
/*                    for a detailed discussion of the definition. */

/* $ Parameters */

/*     None. */

/* $ Exceptions */

/*     1)  If TARGET and OBSRVR are not distinct, the error */
/*         SPICE(BODIESNOTDISTINCT) will be signaled. */

/*     2)  If no SPK (ephemeris) data are available for the observer, */
/*         target, and Sun at the time specified by ET, the error will */
/*         be diagnosed by routines called by this routine.  If light */
/*         time corrections are used, SPK data for the target body must */
/*         be available at the time ET - LT, where LT is the one-way */
/*         light time from the target to the observer at ET. */
/*         Additionally, SPK data must be available for the Sun at the */
/*         time ET - LT - LT2, where LT2 is the light time from the Sun */
/*         to the target body at time ET - LT. */

/*     3)  If PCK data defining the orientation or shape of the target */
/*         body are unavailable, the error will be diagnosed by routines */
/*         called by this routine. */

/*     4)  If no body-fixed frame is associated with the target body, */
/*         the error SPICE(NOFRAME) is signaled. */

/*     5) If name of target or observer cannot be translated to its */
/*        NAIF ID code, the error SPICE(IDCODENOTFOUND) is signaled. */

/* $ Files */

/*     No files are input to this routine.  However, ILLUM expects */
/*     that the appropriate SPK and PCK files have been loaded via */
/*     FURNSH. */

/* $ Particulars */


/*     The term "illumination angles" refers to following set of */
/*     angles: */


/*        solar incidence angle    Angle between the surface normal at */
/*                                 the specified surface point and the */
/*                                 vector from the surface point to the */
/*                                 Sun. */

/*        emission angle           Angle between the surface normal at */
/*                                 the specified surface point and the */
/*                                 vector from the surface point to the */
/*                                 observer. */

/*        phase angle              Angle between the vectors from the */
/*                                 surface point to the observing body's */
/*                                 location and from the surface point */
/*                                 to the Sun. */


/*     The diagram below illustrates the geometrical relationships */
/*     defining these angles.  The labels for the solar incidence, */
/*     emission, and phase angles are "s.i.", "e.", and "phase". */


/*                                                      * */
/*                                                     Sun */

/*                    surface normal vector */
/*                              ._                 _. */
/*                              |\                 /|  Sun vector */
/*                                \    phase      / */
/*                                 \   .    .    / */
/*                                 .            . */
/*                                   \   ___   / */
/*                              .     \/     \/ */
/*                                    _\ s.i./ */
/*                             .    /   \   / */
/*                             .   |  e. \ / */
/*         *             <--------------- *  surface point on */
/*      viewing            vector            target body */
/*      location           to viewing */
/*      (observer)         location */


/*     Note that if the target-observer vector, the target normal vector */
/*     at the surface point, and the target-sun vector are coplanar, */
/*     then phase is the sum of incidence and emission.  This is rarely */
/*     true; usually */

/*        phase angle  <  solar incidence angle + emission angle */

/*     All of the above angles can be computed using light time */
/*     corrections, light time and stellar aberration corrections, or */
/*     no aberration corrections.  The way aberration corrections */
/*     are used is described below. */

/*     Care must be used in computing light time corrections.  The */
/*     guiding principle used here is "describe what appears in */
/*     an image."  We ignore differential light time; the light times */
/*     from all points on the target to the observer are presumed to be */
/*     equal. */


/*        Observer-target body vector */
/*        --------------------------- */

/*        Let ET be the epoch at which an observation or remote */
/*        sensing measurement is made, and let ET - LT ("LT" stands */
/*        for "light time") be the epoch at which the photons received */
/*        at ET were emitted from the body (we use the term "emitted" */
/*        loosely here). */

/*        The correct observer-target vector points from the observer's */
/*        location at ET to the target body's location at ET - LT. */
/*        The target-observer vector points in the opposite direction. */

/*        Since light time corrections are not symmetric, the correct */
/*        target-observer vector CANNOT be found by computing the light */
/*        time corrected position of the observer as seen from the */
/*        target body. */


/*        Target body's orientation */
/*        ------------------------- */

/*        Using the definitions of ET and LT above, the target */
/*        body's orientation at ET - LT is used.  The surface */
/*        normal is dependent on the target body's orientation, so */
/*        the body's orientation model must be evaluated for the correct */
/*        epoch. */


/*        Target body -- Sun vector */
/*        ------------------------- */

/*        All surface features on the target body will appear in */
/*        a measurement made at ET as they were at ET-LT.  In */
/*        particular, lighting on the target body is dependent on */
/*        the apparent location of the Sun as seen from the target */
/*        body at ET-LT.  So, a second light time correction is used */
/*        in finding the apparent location of the Sun. */


/*     Stellar aberration corrections, when used, are applied as follows: */


/*        Observer-target body vector */
/*        --------------------------- */

/*        In addition to light time correction, stellar aberration is */
/*        used in computing the apparent target body position as seen */
/*        from the observer's location at time ET.  This apparent */
/*        position defines the observer-target body vector. */


/*        Target body-Sun vector */
/*        ---------------------- */

/*        The target body-Sun vector is the apparent position of the Sun, */
/*        corrected for light time and stellar aberration, as seen from */
/*        the target body at time ET-LT.  Note that the target body's */
/*        position is not affected by the stellar aberration correction */
/*        applied in finding its apparent position as seen by the */
/*        observer. */


/*     Once all of the vectors, as well as the target body's */
/*     orientation, have been computed with the proper aberration */
/*     corrections, the element of time is eliminated from the */
/*     computation.  The problem becomes a purely geometrical one, */
/*     and is described by the diagram above. */


/* $ 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 phase, solar incidence, and emission angles at the */
/*     sub-solar and sub-spacecraft points on Mars as seen from the */
/*     Mars Global Surveyor spacecraft at a specified UTC time. */
/*     Use light time and stellar aberration corrections. */

/*           PROGRAM ANGLES */
/*           IMPLICIT NONE */
/*     C */
/*     C     SPICELIB functions */
/*     C */
/*           DOUBLE PRECISION      DPR */

/*     C */
/*     C     Local parameters */
/*     C */
/*           INTEGER               NAMLEN */
/*           PARAMETER           ( NAMLEN = 32 ) */

/*           INTEGER               TIMLEN */
/*           PARAMETER           ( TIMLEN = 25 ) */

/*     C */
/*     C     Local variables */
/*     C */
/*           CHARACTER*(NAMLEN)    OBSRVR */
/*           CHARACTER*(NAMLEN)    TARGET */
/*           CHARACTER*(TIMLEN)    UTC */

/*           DOUBLE PRECISION      ALT */
/*           DOUBLE PRECISION      ET */
/*           DOUBLE PRECISION      SSCEMI */
/*           DOUBLE PRECISION      SSCPHS */
/*           DOUBLE PRECISION      SSCSOL */
/*           DOUBLE PRECISION      SSLEMI */
/*           DOUBLE PRECISION      SSLPHS */
/*           DOUBLE PRECISION      SSLSOL */
/*           DOUBLE PRECISION      SSOLPT ( 3 ) */
/*           DOUBLE PRECISION      SSCPT  ( 3 ) */

/*     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 our UTC time to ephemeris seconds past J2000. */
/*     C */
/*           UTC = '2004 JAN 1 12:00:00' */

/*           CALL UTC2ET ( UTC, ET ) */

/*     C */
/*     C     Assign observer and target names.  The acronym MGS */
/*     C     indicates Mars Global Surveyor.  See NAIF_IDS for a */
/*     C     list of names recognized by SPICE. */
/*     C */
/*           TARGET = 'Mars' */
/*           OBSRVR = 'MGS' */

/*     C */
/*     C     Find the sub-solar point on the Earth as seen from */
/*     C     the MGS spacecraft at ET.  Use the "surface intercept" */
/*     C     style of sub-point definition. This makes it easy */
/*     C     to verify the solar incidence angle. */
/*     C */
/*           CALL SUBSOL ( 'Near point', TARGET,  ET, */
/*          .              'LT+S',       OBSRVR,  SSOLPT  ) */

/*     C */
/*     C     Now find the sub-spacecraft point.  Use the */
/*     C     "nearest point" definition of the sub-point */
/*     C     here---this makes it easy to verify the emission angle. */
/*     C */
/*           CALL SUBPT ( 'Near point',  TARGET,  ET, */
/*          .             'LT+S',        OBSRVR,  SSCPT,  ALT ) */

/*     C */
/*     C     Find the phase, solar incidence, and emission */
/*     C     angles at the sub-solar point on the Earth as seen */
/*     C     from Mars Observer at time ET. */
/*     C */
/*           CALL ILLUM ( TARGET, ET,     'LT+S', OBSRVR, */
/*          .             SSOLPT, SSLPHS, SSLSOL, SSLEMI ) */

/*     C */
/*     C     Do the same for the sub-spacecraft point. */
/*     C */
/*           CALL ILLUM ( TARGET, ET,     'LT+S', OBSRVR, */
/*          .             SSCPT,  SSCPHS, SSCSOL, SSCEMI ) */

/*     C */
/*     C     Convert the angles to degrees and write them out. */
/*     C */
/*           SSLPHS = DPR() * SSLPHS */
/*           SSLSOL = DPR() * SSLSOL */
/*           SSLEMI = DPR() * SSLEMI */

/*           SSCPHS = DPR() * SSCPHS */
/*           SSCSOL = DPR() * SSCSOL */
/*           SSCEMI = DPR() * SSCEMI */

/*           WRITE (*,*) ' ' */
/*           WRITE (*,*) 'UTC epoch is ', UTC */
/*           WRITE (*,*) ' ' */
/*           WRITE (*,*) 'Illumination angles at the sub-solar point:' */
/*           WRITE (*,*) ' ' */
/*           WRITE (*,*) 'Phase angle           (deg.): ', SSLPHS */
/*           WRITE (*,*) 'Solar incidence angle (deg.): ', SSLSOL */
/*           WRITE (*,*) 'Emission angle        (deg.): ', SSLEMI */
/*           WRITE (*,*) ' ' */
/*           WRITE (*,*) 'The solar incidence angle should be 0.' */
/*           WRITE (*,*) 'The emission and phase angles should be equal.' */

/*           WRITE (*,*) ' ' */
/*           WRITE (*,*) 'Illumination angles at the sub-s/c point:' */
/*           WRITE (*,*) ' ' */
/*           WRITE (*,*) 'Phase angle           (deg.): ', SSCPHS */
/*           WRITE (*,*) 'Solar incidence angle (deg.): ', SSCSOL */
/*           WRITE (*,*) 'Emission angle        (deg.): ', SSCEMI */
/*           WRITE (*,*) ' ' */
/*           WRITE (*,*) 'The emission angle should be 0.' */
/*           WRITE (*,*) 'The solar incidence and phase angles should '// */
/*          .            'be equal.' */

/*           END */


/*     When this program is executed, the output will be: */


/*        UTC epoch is 2004 JAN 1 12:00:00 */

/*        Illumination angles at the sub-solar point: */

/*        Phase angle           (deg.):   150.210714 */
/*        Solar incidence angle (deg.):   6.3735213E-15 */
/*        Emission angle        (deg.):   150.210714 */

/*        The solar incidence angle should be 0. */
/*        The emission and phase angles should be equal. */

/*        Illumination angles at the sub-s/c point: */

/*        Phase angle           (deg.):   123.398202 */
/*        Solar incidence angle (deg.):   123.398202 */
/*        Emission angle        (deg.):   6.36110936E-15 */

/*        The emission angle should be 0. */
/*        The solar incidence and phase angles should be equal. */


/* $ Restrictions */

/*     None. */

/* $ Literature_References */

/*     None. */

/* $ Author_and_Institution */

/*     C.H. Acton     (JPL) */
/*     N.J. Bachman   (JPL) */

/* $ Version */

/* -    SPICELIB Version 1.2.1, 07-FEB-2008 (NJB) */

/*        Abstract now states that this routine is deprecated. */

/* -    SPICELIB Version 1.2.0, 23-OCT-2005 (NJB) */

/*        Updated to remove non-standard use of duplicate arguments */
/*        in VSUB calls.  Replaced call to BODVAR with call to BODVCD. */

/* -    SPICELIB Version 1.1.0, 22-JUL-2004 (NJB) */

/*        Updated to support representations of integers in the input */
/*        arguments TARGET and OBSRVR. */

/* -    SPICELIB Version 1.0.2, 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 1.0.1, 10-JUL-2002 (NJB) */

/*        Updated Index_Entries header section. */

/* -    SPICELIB Version 1.0.0, 21-MAR-1999 (NJB) */

/*        Adapted from the MGSSPICE version dated 10-MAR-1992. */
/* -& */
/* $ Index_Entries */

/*     illumination angles */
/*     lighting angles */
/*     phase angle */
/*     solar incidence angle */
/*     emission angle */

/* -& */
/* $ Revisions */

/* -    SPICELIB Version 1.2.0, 23-OCT-2005 (NJB) */

/*        Updated to remove non-standard use of duplicate arguments */
/*        in VSUB calls.  Replaced call to BODVAR with call to BODVCD. */

/* -    SPICELIB Version 1.1.0, 22-JUL-2004 (NJB) */

/*        Updated to support representations of integers in the */
/*        input arguments TARGET and OBSRVR:  calls to BODN2C */
/*        were replaced by calls to BODS2C. */

/* -& */

/*     SPICELIB functions */


/*     Local parameters */


/*     Local variables */


/*     Standard SPICE error handling. */

    if (return_()) {
	return 0;
    } else {
	chkin_("ILLUM", (ftnlen)5);
    }

/*     Obtain integer codes for the target and observer. */

    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_("ILLUM", (ftnlen)5);
	return 0;
    }
    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_("ILLUM", (ftnlen)5);
	return 0;
    }

/*     The observer and target must be distinct. */

    if (trgcde == obscde) {
	setmsg_("Target is #; observer is #.", (ftnlen)27);
	errch_("#", target, (ftnlen)1, target_len);
	errch_("#", obsrvr, (ftnlen)1, obsrvr_len);
	sigerr_("SPICE(BODIESNOTDISTINCT)", (ftnlen)24);
	chkout_("ILLUM", (ftnlen)5);
	return 0;
    }

/*     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_("ILLUM", (ftnlen)5);
	return 0;
    }

/*     Find the body-fixed state of the target as seen from the observer */
/*     at ET.  The appropriate aberration corrections will be used in */
/*     evaluating this state. */

    spkez_(&trgcde, et, frname, abcorr, &obscde, tstate, &lt, (ftnlen)80, 
	    abcorr_len);

/*     Determine the epoch to be used in computing the target-Sun vector. */

    if (eqstr_(abcorr, "NONE", abcorr_len, (ftnlen)4)) {
	tepoch = *et;
    } else {
	tepoch = *et - lt;
    }

/*     Find the body-fixed state of the Sun as seen from the target at */
/*     TEPOCH. */

    spkez_(&c__10, &tepoch, frname, abcorr, &trgcde, sstate, &lts, (ftnlen)80,
	     abcorr_len);

/*     Grab the position portions of the states (the first three */
/*     elements of each state).  Negate the observer-target vector, */
/*     since the vector required for the illumination angle */
/*     computation is the target-observer vector.  The vectors we've */
/*     found point from the target body center to the observer and */
/*     Sun, and already take light time corrections into account. */

    vminus_(tstate, obsvec);
    vequ_(sstate, sunvec);

/*     Now we'll modify target-observer and target-Sun vectors to */
/*     take into account the offset between the target center and the */
/*     surface point of interest; we want the vectors to point from */
/*     the surface point to the observer and Sun respectively. */

    vsub_(obsvec, spoint, offobs);
    vsub_(sunvec, spoint, offsun);

/*     Find the surface normal at SPOINT.  We'll need the radii of the */
/*     target body. */

    bodvcd_(&trgcde, "RADII", &c__3, &n, radii, (ftnlen)5);
    surfnm_(radii, &radii[1], &radii[2], spoint, normal);

/*     Find the illumination angles.  VSEP will give us angular */
/*     separation in radians. */

    *phase = vsep_(offsun, offobs);
    *solar = vsep_(normal, offsun);
    *emissn = vsep_(normal, offobs);
    chkout_("ILLUM", (ftnlen)5);
    return 0;
} /* illum_ */

