/* gfrfov.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 doublereal c_b13 = 1e-6;
static logical c_false = FALSE_;

/* $Procedure      GFRFOV ( GF, is ray in FOV? ) */
/* Subroutine */ int gfrfov_(char *inst, doublereal *raydir, char *rframe, 
	char *abcorr, char *obsrvr, doublereal *step, doublereal *cnfine, 
	doublereal *result, ftnlen inst_len, ftnlen rframe_len, ftnlen 
	abcorr_len, ftnlen obsrvr_len)
{
    /* System generated locals */
    integer i__1;

    /* Local variables */
    extern /* Subroutine */ int chkin_(char *, ftnlen), errdp_(char *, 
	    doublereal *, ftnlen);
    extern integer sized_(doublereal *);
    extern logical gfbail_();
    extern /* Subroutine */ int gfrefn_(), gfrepf_(), gfrepi_();
    extern /* Subroutine */ int gffove_(char *, char *, doublereal *, char *, 
	    char *, char *, char *, doublereal *, U_fp, U_fp, logical *, U_fp,
	     U_fp, U_fp, logical *, L_fp, doublereal *, doublereal *, ftnlen, 
	    ftnlen, ftnlen, ftnlen, ftnlen, ftnlen);
    extern /* Subroutine */ int gfrepu_(), gfstep_();
    extern /* Subroutine */ int setmsg_(char *, ftnlen), errint_(char *, 
	    integer *, ftnlen), sigerr_(char *, ftnlen);
    extern logical return_(void);
    extern /* Subroutine */ int chkout_(char *, ftnlen), gfsstp_(doublereal *)
	    ;

/* $ Abstract */

/*     Determine time intervals when a specified ray intersects the */
/*     space bounded by the field-of-view (FOV) of a specified */
/*     instrument. */

/* $ 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 */

/*     CK */
/*     FRAMES */
/*     GF */
/*     KERNEL */
/*     NAIF_IDS */
/*     PCK */
/*     SPK */
/*     TIME */
/*     WINDOWS */

/* $ Keywords */

/*     EVENT */
/*     FOV */
/*     GEOMETRY */
/*     INSTRUMENT */
/*     SEARCH */
/*     WINDOW */

/* $ Declarations */
/* $ Abstract */

/*     This file contains public, global parameter declarations */
/*     for the SPICELIB Geometry Finder (GF) subsystem. */

/* $ 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 */

/*     GF */

/* $ Keywords */

/*     GEOMETRY */
/*     ROOT */

/* $ Restrictions */

/*     None. */

/* $ Author_and_Institution */

/*     N.J. Bachman      (JPL) */
/*     L.E. Elson        (JPL) */
/*     E.D. Wright       (JPL) */

/* $ Literature_References */

/*     None. */

/* $ Version */

/* -    SPICELIB Version 1.0.0, 21-FEB-2009 (NJB) (LSE) (EDW) */

/* -& */

/*     Root finding parameters: */

/*     CNVTOL is the default convergence tolerance used by the */
/*     high-level GF search API routines. This tolerance is */
/*     used to terminate searches for binary state transitions: */
/*     when the time at which a transition occurs is bracketed */
/*     by two times that differ by no more than CNVTOL, the */
/*     transition time is considered to have been found. */

/*     Units are TDB seconds. */


/*     NWMAX is the maximum number of windows allowed for user-defined */
/*     workspace array. */

/*        DOUBLE PRECISION      WORK   ( LBCELL : MW, NWMAX ) */

/*     Currently no more than twelve windows are required; the three */
/*     extra windows are spares. */

/*     Callers of GFEVNT can include this file and use the parameter */
/*     NWMAX to declare the second dimension of the workspace array */
/*     if necessary. */


/*     Callers of GFIDST should declare their workspace window */
/*     count using NWDIST. */


/*     Callers of GFSEP should declare their workspace window */
/*     count using NWSEP. */


/*     ADDWIN is a parameter used to expand each interval of the search */
/*     (confinement) window by a small amount at both ends in order to */
/*     accommodate searches using equality constraints. The loaded */
/*     kernel files must accommodate these expanded time intervals. */


/*     FRMNLN is a string length for frame names. */


/*     NVRMAX is the maximum number of vertices if FOV type is "POLYGON" */


/*     FOVTLN -- maximum length for FOV string. */


/*     Specify the character strings that are allowed in the */
/*     specification of field of view shapes. */


/*     Character strings that are allowed in the */
/*     specification of occultation types: */


/*     Occultation target shape specifications: */


/*     Specify the number of supported occultation types and occultation */
/*     type string length: */


/*     Instrument field-of-view (FOV) parameters */

/*     Maximum number of FOV boundary vectors: */


/*     FOV shape parameters: */

/*        circle */
/*        ellipse */
/*        polygon */
/*        rectangle */


/*     End of file gf.inc. */

/* $ Brief_I/O */

/*     VARIABLE  I/O  DESCRIPTION */
/*     --------  ---  -------------------------------------------------- */
/*     MARGIN     P   Minimum complement of FOV cone angle. */
/*     LBCELL     P   SPICE Cell lower bound. */
/*     CNVTOL     P   Convergence tolerance. */
/*     MAXVRT     P   Maximum number of FOV boundary vertices. */
/*     INST       I   Name of the instrument. */
/*     RAYDIR     I   Ray's direction vector. */
/*     RFRAME     I   Reference frame of ray's direction vector. */
/*     ABCORR     I   Aberration correction flag. */
/*     OBSRVR     I   Name of the observing body. */
/*     STEP       I   Step size in seconds for finding FOV events. */
/*     CNFINE     I   SPICE window to which the search is restricted. */
/*     RESULT     O   SPICE window containing results. */


/* $ Detailed_Input */


/*     INST       indicates the name of an instrument, such as a */
/*                spacecraft-mounted framing camera, the field of view */
/*                (FOV) of which is to be used for an target intersection */
/*                search: the direction from the observer to a target */
/*                is represented by a ray, and times when the specified */
/*                ray intersects the region of space bounded by the FOV */
/*                are sought. */

/*                The position of the instrument designated by INST is */
/*                considered to coincide with that of the ephemeris */
/*                object designated by the input argument OBSRVR (see */
/*                description below). */

/*                INST must have a corresponding NAIF ID and a frame */
/*                defined, as is normally done in a frame kernel. It */
/*                must also have an associated reference frame and a FOV */
/*                shape, boresight and boundary vertices (or reference */
/*                vector and reference angles) defined, as is usually */
/*                done in an instrument kernel. */

/*                See the header of the SPICELIB routine GETFOV for a */
/*                description of the required parameters associated with */
/*                an instrument. */


/*     RAYDIR     is the direction vector associated with a ray */
/*                representing a target. The ray emanates from the */
/*                location of the ephemeris object designated by the */
/*                input argument OBSRVR and is expressed relative to the */
/*                reference frame designated by RFRAME (see descriptions */
/*                below). */


/*     RFRAME     is the name of the reference frame associated with */
/*                the input ray's direction vector RAYDIR. */

/*                Since light time corrections are not supported for */
/*                rays, the orientation of the frame is always evaluated */
/*                at the epoch associated with the observer, as opposed */
/*                to the epoch associated with the light-time corrected */
/*                position of the frame center. */

/*                Case and leading or trailing blanks bracketing a */
/*                non-blank frame name are not significant in the string */
/*                RFRAME. */


/*     ABCORR     indicates the aberration corrections to be applied */
/*                when computing the ray's direction. */

/*                The supported aberration correction options are */

/*                   'NONE'          No correction. */
/*                   'S'             Stellar aberration correction, */
/*                                   reception case. */
/*                   'XS'            Stellar aberration correction, */
/*                                   transmission case. */

/*                For detailed information, see the geometry finder */
/*                required reading, gf.req. */

/*                Case, leading and trailing blanks are not significant */
/*                in the string ABCORR. */


/*     OBSRVR     is the name of the body from which the target */
/*                represented by RAYDIR is observed. The instrument */
/*                designated by INST is treated as if it were co-located */
/*                with the observer. */
/*                Optionally, you may supply the integer NAIF ID code */
/*                for the body as a string. */

/*                Case and leading or trailing blanks are not */
/*                significant in the string OBSRVR. */


/*     STEP       is the step size to be used in the search. STEP must */
/*                be shorter than any interval, within the confinement */
/*                window, over which the specified condition is met. In */
/*                other words, STEP must be shorter than the shortest */
/*                visibility event that the user wishes to detect. STEP */
/*                also must be shorter than the minimum duration */
/*                separating any two visibility events. However, STEP */
/*                must not be *too* short, or the search will take an */
/*                unreasonable amount of time. */

/*                The choice of STEP affects the completeness but not */
/*                the precision of solutions found by this routine; the */
/*                precision is controlled by the convergence tolerance. */
/*                See the discussion of the parameter CNVTOL for */
/*                details. */

/*                STEP has units of seconds. */


/*     CNFINE     is a SPICE window that confines the time period over */
/*                which the specified search is conducted. CNFINE may */
/*                consist of a single interval or a collection of */
/*                intervals. */

/*                The endpoints of the time intervals comprising CNFINE */
/*                are interpreted as seconds past J2000 TDB. */

/*                See the Examples section below for a code example */
/*                that shows how to create a confinement window. */

/*                CNFINE must be initialized by the caller via the */
/*                SPICELIB routine SSIZED. */

/* $ Detailed_Output */


/*     RESULT     is a SPICE window representing the set of time */
/*                intervals, within the confinement period, when the */
/*                input ray is "visible"; that is, when the ray is */
/*                contained in the space bounded by the specified */
/*                instrument's field of view. */

/*                The endpoints of the time intervals comprising RESULT */
/*                are interpreted as seconds past J2000 TDB. */

/*                If RESULT is non-empty on input, its contents */
/*                will be discarded before GFRFOV conducts its */
/*                search. */

/* $ Parameters */

/*     LBCELL     is the lower bound for SPICE cell arrays. */

/*     CNVTOL     is the convergence tolerance used for finding */
/*                endpoints of the intervals comprising the result */
/*                window. CNVTOL is used to determine when binary */
/*                searches for roots should terminate: when a root is */
/*                bracketed within an interval of length CNVTOL; the */
/*                root is considered to have been found. */

/*                The accuracy, as opposed to precision, of roots found */
/*                by this routine depends on the accuracy of the input */
/*                data. In most cases, the accuracy of solutions will be */
/*                inferior to their precision. */

/*     MAXVRT     is the maximum number of vertices that may be used */
/*                to define the boundary of the specified instrument's */
/*                field of view. */

/*     MARGIN     is a small positive number used to constrain the */
/*                orientation of the boundary vectors of polygonal */
/*                FOVs. Such FOVs must satisfy the following constraints: */

/*                   1)  The boundary vectors must be contained within */
/*                       a right circular cone of angular radius less */
/*                       than than (pi/2) - MARGIN radians; in other */
/*                       words, there must be a vector A such that all */
/*                       boundary vectors have angular separation from */
/*                       A of less than (pi/2)-MARGIN radians. */

/*                   2)  There must be a pair of boundary vectors U, V */
/*                       such that all other boundary vectors lie in */
/*                       the same half space bounded by the plane */
/*                       containing U and V. Furthermore, all other */
/*                       boundary vectors must have orthogonal */
/*                       projections onto a specific plane normal to */
/*                       this plane (the normal plane contains the angle */
/*                       bisector defined by U and V) such that the */
/*                       projections have angular separation of at least */
/*                       2*MARGIN radians from the plane spanned by U */
/*                       and V. */

/*                 MARGIN is currently set to 1.D-12. */


/*     See INCLUDE file gf.inc for declarations and descriptions of */
/*     parameters used throughout the GF system. */

/* $ Exceptions */


/*     1)  In order for this routine to produce correct results, */
/*         the step size must be appropriate for the problem at hand. */
/*         Step sizes that are too large may cause this routine to miss */
/*         roots; step sizes that are too small may cause this routine */
/*         to run unacceptably slowly and in some cases, find spurious */
/*         roots. */

/*         This routine does not diagnose invalid step sizes, except */
/*         that if the step size is non-positive, the error */
/*         SPICE(INVALIDSTEPSIZE) will be signaled. */

/*     2)  Due to numerical errors, in particular, */

/*            - Truncation error in time values */
/*            - Finite tolerance value */
/*            - Errors in computed geometric quantities */

/*         it is *normal* for the condition of interest to not always be */
/*         satisfied near the endpoints of the intervals comprising the */
/*         result window. */

/*         The result window may need to be contracted slightly by the */
/*         caller to achieve desired results. The SPICE window routine */
/*         WNCOND can be used to contract the result window. */

/*     3)  If the observer's name cannot be mapped to an ID code, the */
/*         error SPICE(IDCODENOTFOUND) is signaled. */

/*     4)  If the aberration correction flag calls for light time */
/*         correction, the error SPICE(INVALIDOPTION) is signaled. */

/*     5)  If the ray's direction vector is zero, the error */
/*         SPICE(ZEROVECTOR) is signaled. */

/*     6)  If the instrument name INST does not have corresponding NAIF */
/*         ID code, the error will be diagnosed by a routine in the call */
/*         tree of this routine. */

/*     7)  If the FOV parameters of the instrument are not present in */
/*         the kernel pool, the error will be be diagnosed by routines */
/*         in the call tree of this routine. */

/*     8)  If the FOV boundary has more than MAXVRT vertices, the error */
/*         will be be diagnosed by routines in the call tree of this */
/*         routine. */

/*     9)  If the instrument FOV is polygonal, and this routine cannot */
/*         find a ray R emanating from the FOV vertex such that maximum */
/*         angular separation of R and any FOV boundary vector is within */
/*         the limit (pi/2)-MARGIN radians, the error will be diagnosed */
/*         by a routine in the call tree of this routine. If the FOV */
/*         is any other shape, the same error check will be applied with */
/*         the instrument boresight vector serving the role of R. */

/*     10) If the loaded kernels provide insufficient data to compute a */
/*         requested state vector, the error will be diagnosed by a */
/*         routine in the call tree of this routine. */

/*     11) If an error occurs while reading an SPK or other kernel file, */
/*         the error will be diagnosed by a routine in the call tree */
/*         of this routine. */

/*     12) If the output SPICE window RESULT has insufficient capacity */
/*         to contain the number of intervals on which the specified */
/*         visibility condition is met, the error will be diagnosed */
/*         by a routine in the call tree of this routine. If the result */
/*         window has size less than 2, the error SPICE(WINDOWTOOSMALL) */
/*         will be signaled by this routine. */

/* $ Files */

/*     Appropriate SPICE kernels must be loaded by the calling program */
/*     before this routine is called. */

/*     The following data are required: */

/*        - SPK data:  ephemeris data for the observer for the period */
/*          defined by the confinement window 'CNFINE' must be loaded. */
/*          If aberration corrections are used, the state of the */
/*          observer relative to the solar system barycenter must be */
/*          calculable from the available ephemeris data. Typically */
/*          ephemeris data are made available by loading one or more SPK */
/*          files via FURNSH. */

/*        - Data defining the reference frame associated with the */
/*          instrument designated by INST must be available in the kernel */
/*          pool. Additionally the name INST must be associated with an */
/*          ID code. Normally these data are  made available by loading */
/*          a frame kernel via FURNSH. */

/*        - IK data: the kernel pool must contain data such that */
/*          the SPICELIB routine GETFOV may be called to obtain */
/*          parameters for INST. Normally such data are provided by */
/*          an IK via FURNSH. */

/*     The following data may be required: */

/*        - CK data: if the instrument frame is fixed to a spacecraft, */
/*          at least one CK file will be needed to permit transformation */
/*          of vectors between that frame and the J2000 frame. */

/*        - SCLK data: if a CK file is needed, an associated SCLK */
/*          kernel is required to enable conversion between encoded SCLK */
/*          (used to time-tag CK data) and barycentric dynamical time */
/*          (TDB). */

/*        - Since the input ray direction may be expressed in any */
/*          frame, FKs, CKs, SCLK kernels, PCKs, and SPKs may be */
/*          required to map the direction to the J2000 frame. */

/*     Kernel data are normally loaded once per program run, NOT every */
/*     time this routine is called. */

/* $ Particulars */

/*     This routine determines a set of one or more time intervals when */
/*     the specified ray in contained within the field of view of a */
/*     specified instrument. We'll use the term "visibility event" to */
/*     designate such an appearance. The set of time intervals resulting */
/*     from the search is returned as a SPICE window. */

/*     This routine provides a simpler, but less flexible, interface */
/*     than does the SPICELIB routine GFFOVE for conducting searches for */
/*     visibility events. Applications that require support for progress */
/*     reporting, interrupt handling, non-default step or refinement */
/*     functions, or non-default convergence tolerance should call */
/*     GFFOVE rather than this routine. */

/*     Below we discuss in greater detail aspects of this routine's */
/*     solution process that are relevant to correct and efficient use */
/*     of this routine in user applications. */


/*     The Search Process */
/*     ================== */

/*     The search for visibility events is treated as a search for state */
/*     transitions: times are sought when the state of the ray */
/*     changes from "not visible" to "visible" or vice versa. */

/*     Step Size */
/*     ========= */

/*     Each interval of the confinement window is searched as follows: */
/*     first, the input step size is used to determine the time */
/*     separation at which the visibility state will be sampled. */
/*     Starting at the left endpoint of an interval, samples will be */
/*     taken at each step. If a state change is detected, a root has */
/*     been bracketed; at that point, the "root"--the time at which the */
/*     state change occurs---is found by a refinement process, for */
/*     example, via binary search. */

/*     Note that the optimal choice of step size depends on the lengths */
/*     of the intervals over which the visibility state is constant: */
/*     the step size should be shorter than the shortest visibility event */
/*     duration and the shortest period between visibility events, within */
/*     the confinement window. */

/*     Having some knowledge of the relative geometry of the ray and */
/*     observer can be a valuable aid in picking a reasonable step size. */
/*     In general, the user can compensate for lack of such knowledge by */
/*     picking a very short step size; the cost is increased computation */
/*     time. */

/*     Note that the step size is not related to the precision with which */
/*     the endpoints of the intervals of the result window are computed. */
/*     That precision level is controlled by the convergence tolerance. */


/*     Convergence Tolerance */
/*     ===================== */

/*     Once a root has been bracketed, a refinement process is used to */
/*     narrow down the time interval within which the root must lie. */
/*     This refinement process terminates when the location of the root */
/*     has been determined to within an error margin called the */
/*     "convergence tolerance." The convergence tolerance used by this */
/*     routine is set via the parameter CNVTOL. */

/*     The value of CNVTOL is set to a "tight" value so that the */
/*     tolerance doesn't become the limiting factor in the accuracy of */
/*     solutions found by this routine. In general the accuracy of input */
/*     data will be the limiting factor. */

/*     To use a different tolerance value, a lower-level GF routine such */
/*     as GFFOVE  must be called. Making the tolerance tighter than */
/*     CNVTOL is unlikely to be useful, since the results are unlikely */
/*     to be more accurate. Making the tolerance looser will speed up */
/*     searches somewhat, since a few convergence steps will be omitted. */
/*     However, in most cases, the step size is likely to have a much */
/*     greater effect on processing time than would the convergence */
/*     tolerance. */


/*     The Confinement Window */
/*     ====================== */

/*     The simplest use of the confinement window is to specify a time */
/*     interval within which a solution is sought. However, the */
/*     confinement window can, in some cases, be used to make searches */
/*     more efficient. Sometimes it's possible to do an efficient search */
/*     to reduce the size of the time period over which a relatively */
/*     slow search of interest must be performed. For an example, see */
/*     the program CASCADE in the GF Example Programs chapter of the GF */
/*     Required Reading, gf.req. */

/* $ Examples */


/*     The numerical results shown for these examples may differ across */
/*     platforms. The results depend on the SPICE kernels used as */
/*     input, the compiler and supporting libraries, and the machine */
/*     specific arithmetic implementation. */


/*     1) This example is an extension of example #1 in the */
/*        header of */

/*           GFTFOV */

/*        The problem statement for that example is */

/*           Search for times when Saturn's satellite Phoebe is within */
/*           the FOV of the Cassini narrow angle camera */
/*           (CASSINI_ISS_NAC). To simplify the problem, restrict the */
/*           search to a short time period where continuous Cassini bus */
/*           attitude data are available. */

/*           Use a step size of 10 seconds to reduce chances of missing */
/*           short visibility events. */

/*        Here we search the same confinement window for times when a */
/*        selected background star is visible. We use the FOV of the */
/*        Cassini ISS wide angle camera (CASSINI_ISS_WAC) to enhance the */
/*        probability of viewing the star. */

/*        The star we'll use has catalog number 6000 in the Hipparcos */
/*        Catalog. The star's J2000 right ascension and declination, */
/*        proper motion, and parallax are taken from that catalog. */

/*        Use the meta-kernel from the GFTFOV example: */


/*           KPL/MK */

/*           File name: gftfov_ex1.tm */

/*           This meta-kernel is intended to support operation of SPICE */
/*           example programs. The kernels shown here should not be */
/*           assumed to contain adequate or correct versions of data */
/*           required by SPICE-based user applications. */

/*           In order for an application to use this meta-kernel, the */
/*           kernels referenced here must be present in the user's */
/*           current working directory. */

/*           The names and contents of the kernels referenced */
/*           by this meta-kernel are as follows: */

/*              File name                     Contents */
/*              ---------                     -------- */
/*              naif0009.tls                  Leapseconds */
/*              cpck05Mar2004.tpc             Satellite orientation and */
/*                                            radii */
/*              981005_PLTEPH-DE405S.bsp      Planetary ephemeris */
/*              020514_SE_SAT105.bsp          Satellite ephemeris */
/*              030201AP_SK_SM546_T45.bsp     Spacecraft ephemeris */
/*              cas_v37.tf                    Cassini FK */
/*              04135_04171pc_psiv2.bc        Cassini bus CK */
/*              cas00084.tsc                  Cassini SCLK kernel */
/*              cas_iss_v09.ti                Cassini IK */


/*           \begindata */

/*              KERNELS_TO_LOAD = ( 'naif0009.tls', */
/*                                  'cpck05Mar2004.tpc', */
/*                                  '981005_PLTEPH-DE405S.bsp', */
/*                                  '020514_SE_SAT105.bsp', */
/*                                  '030201AP_SK_SM546_T45.bsp', */
/*                                  'cas_v37.tf', */
/*                                  '04135_04171pc_psiv2.bc', */
/*                                  'cas00084.tsc', */
/*                                  'cas_iss_v09.ti'            ) */
/*           \begintext */



/*        Example code begins here. */


/*           PROGRAM EX1 */
/*           IMPLICIT NONE */
/*     C */
/*     C     SPICELIB functions */
/*     C */
/*           DOUBLE PRECISION      J1950 */
/*           DOUBLE PRECISION      J2000 */
/*           DOUBLE PRECISION      JYEAR */
/*           DOUBLE PRECISION      RPD */

/*           INTEGER               WNCARD */

/*     C */
/*     C     Local parameters */
/*     C */
/*           CHARACTER*(*)         META */
/*           PARAMETER           ( META   = 'gftfov_ex1.tm' ) */

/*           CHARACTER*(*)         TIMFMT */
/*           PARAMETER           ( TIMFMT = */
/*          .      'YYYY-MON-DD HR:MN:SC.######::TDB (TDB)' ) */


/*           DOUBLE PRECISION      AU */
/*           PARAMETER           ( AU     = 149597870.693D0 ) */

/*           INTEGER               LBCELL */
/*           PARAMETER           ( LBCELL = -5 ) */

/*           INTEGER               MAXWIN */
/*           PARAMETER           ( MAXWIN = 10000 ) */

/*           INTEGER               CORLEN */
/*           PARAMETER           ( CORLEN = 10 ) */

/*           INTEGER               BDNMLN */
/*           PARAMETER           ( BDNMLN = 36 ) */

/*           INTEGER               FRNMLN */
/*           PARAMETER           ( FRNMLN = 32 ) */

/*           INTEGER               TIMLEN */
/*           PARAMETER           ( TIMLEN = 35 ) */

/*           INTEGER               LNSIZE */
/*           PARAMETER           ( LNSIZE = 80 ) */

/*     C */
/*     C     Local variables */
/*     C */
/*           CHARACTER*(CORLEN)    ABCORR */
/*           CHARACTER*(BDNMLN)    INST */
/*           CHARACTER*(LNSIZE)    LINE */
/*           CHARACTER*(BDNMLN)    OBSRVR */
/*           CHARACTER*(FRNMLN)    RFRAME */
/*           CHARACTER*(TIMLEN)    TIMSTR ( 2 ) */

/*           DOUBLE PRECISION      CNFINE ( LBCELL : MAXWIN ) */
/*           DOUBLE PRECISION      DEC */
/*           DOUBLE PRECISION      DECEPC */
/*           DOUBLE PRECISION      DECPM */
/*           DOUBLE PRECISION      DECDEG */
/*           DOUBLE PRECISION      DECDG0 */
/*           DOUBLE PRECISION      DTDEC */
/*           DOUBLE PRECISION      DTRA */
/*           DOUBLE PRECISION      ENDPT  ( 2 ) */
/*           DOUBLE PRECISION      ET0 */
/*           DOUBLE PRECISION      ET1 */
/*           DOUBLE PRECISION      LT */
/*           DOUBLE PRECISION      PARLAX */
/*           DOUBLE PRECISION      PLXDEG */
/*           DOUBLE PRECISION      POS    ( 3 ) */
/*           DOUBLE PRECISION      PSTAR  ( 3 ) */
/*           DOUBLE PRECISION      RA */
/*           DOUBLE PRECISION      RADEG */
/*           DOUBLE PRECISION      RADEG0 */
/*           DOUBLE PRECISION      RAEPC */
/*           DOUBLE PRECISION      RAPM */
/*           DOUBLE PRECISION      RAYDIR ( 3 ) */
/*           DOUBLE PRECISION      RESULT ( LBCELL : MAXWIN ) */
/*           DOUBLE PRECISION      RSTAR */
/*           DOUBLE PRECISION      STEPSZ */
/*           DOUBLE PRECISION      T */

/*           INTEGER               CATNO */
/*           INTEGER               I */
/*           INTEGER               J */
/*           INTEGER               N */

/*     C */
/*     C     Load kernels. */
/*     C */
/*           CALL FURNSH ( META ) */

/*     C */
/*     C     Initialize windows. */
/*     C */
/*           CALL SSIZED ( MAXWIN, CNFINE ) */
/*           CALL SSIZED ( MAXWIN, RESULT ) */

/*     C */
/*     C     Insert search time interval bounds into the */
/*     C     confinement window. */
/*     C */
/*           CALL STR2ET ( '2004 JUN 11 06:30:00 TDB', ET0 ) */
/*           CALL STR2ET ( '2004 JUN 11 12:00:00 TDB', ET1 ) */

/*           CALL WNINSD ( ET0, ET1, CNFINE ) */

/*     C */
/*     C     Initialize inputs for the search. */
/*     C */
/*           INST   = 'CASSINI_ISS_WAC' */

/*     C */
/*     C     Create a unit direction vector pointing from */
/*     c     observer to star. We'll assume the direction */
/*     C     is constant during the confinement window, and */
/*     C     we'll use et0 as the epoch at which to compute the */
/*     C     direction from the spacecraft to the star. */
/*     C */
/*     C     The data below are for the star with catalog */
/*     C     number 6000 in the Hipparcos catalog. Angular */
/*     C     units are degrees; epochs have units of Julian */
/*     C     years and have a reference epoch of J1950. */
/*     C     The reference frame is J2000. */
/*     C */
/*           CATNO  = 6000 */

/*           PLXDEG = 0.000001056D0 */

/*           RADEG0 = 19.290789927D0 */
/*           RAPM   = -0.000000720D0 */
/*           RAEPC  = 41.2000D0 */

/*           DECDG0 =  2.015271007D0 */
/*           DECPM  =  0.000001814D0 */
/*           DECEPC = 41.1300D0 */

/*           RFRAME = 'J2000' */

/*     C */
/*     C     Correct the star's direction for proper motion. */
/*     C */
/*     C     The argument t represents et0 as Julian years */
/*     C     past J1950. */
/*     C */
/*           T      =      ET0/JYEAR() */
/*          .         +  ( J2000()- J1950() ) / 365.25D0 */

/*           DTRA   = T - RAEPC */
/*           DTDEC  = T - DECEPC */

/*           RADEG  = RADEG0  +  DTRA  * RAPM */
/*           DECDEG = DECDG0  +  DTDEC * DECPM */

/*           RA     = RADEG  * RPD() */
/*           DEC    = DECDEG * RPD() */

/*           CALL RADREC ( 1.D0, RA, DEC, PSTAR ) */

/*     C */
/*     C     Correct star position for parallax applicable at */
/*     C     the Cassini orbiter's position. (The parallax effect */
/*     C     is negligible in this case; we're simply demonstrating */
/*     C     the computation.) */
/*     C */
/*           PARLAX = PLXDEG * RPD() */
/*           RSTAR  = AU / TAN(PARLAX) */

/*     C */
/*     C     Scale the star's direction vector by its distance from */
/*     C     the solar system barycenter. Subtract off the position */
/*     C     of the spacecraft relative to the solar system barycenter; */
/*     C     the result is the ray's direction vector. */
/*     C */
/*           CALL VSCLIP ( RSTAR, PSTAR ) */

/*           CALL SPKPOS ( 'CASSINI', ET0, 'J2000',  'NONE', */
/*          .              'SOLAR SYSTEM BARYCENTER', POS,  LT ) */

/*           CALL VSUB   ( PSTAR, POS, RAYDIR ) */

/*     C */
/*     C     Correct the star direction for stellar aberration when */
/*     C     we conduct the search. */
/*     C */
/*           ABCORR = 'S' */
/*           OBSRVR = 'CASSINI' */
/*           STEPSZ = 10.D0 */

/*           WRITE (*,*) ' ' */
/*           WRITE (*,*) 'Instrument:              '//INST */
/*           WRITE (*,*) 'Star''s catalog number:  ', CATNO */
/*           WRITE (*,*) ' ' */

/*     C */
/*     C     Perform the search. */
/*     C */
/*           CALL GFRFOV ( INST,   RAYDIR, RFRAME, ABCORR, */
/*          .              OBSRVR, STEPSZ, CNFINE, RESULT ) */

/*           N = WNCARD( RESULT ) */

/*           IF ( N .EQ. 0 ) THEN */

/*              WRITE (*,*) 'No FOV intersection found.' */

/*           ELSE */

/*              WRITE (*,*) */
/*          .   ' Visibility start time              Stop time' */

/*              DO I = 1, N */

/*                 CALL WNFETD ( RESULT, I, ENDPT(1), ENDPT(2) ) */

/*                 DO J = 1, 2 */
/*                    CALL TIMOUT ( ENDPT(J), TIMFMT, TIMSTR(J) ) */
/*                 END DO */

/*                 LINE( :3) = ' ' */
/*                 LINE(2: ) = TIMSTR(1) */
/*                 LINE(37:) = TIMSTR(2) */

/*                 WRITE (*,*) LINE */

/*              END DO */

/*           END IF */

/*           WRITE (*,*) ' ' */
/*           END */


/*        When this program was executed on a PC/Linux/g77 platform, the */
/*        output was: */


/*  Instrument:              CASSINI_ISS_WAC */
/*  Star's catalog number:   6000 */

/*   Visibility start time              Stop time */
/*   2004-JUN-11 06:30:00.000000 (TDB)  2004-JUN-11 12:00:00.000000 (TDB) */


/*     The star is visible throughout the confinement window. */


/* $ Restrictions */

/*     The kernel files to be used by GFRFOV must be loaded (normally via */
/*     the SPICELIB routine FURNSH) before GFRFOV is called. */

/* $ Literature_References */

/*     None. */

/* $ Author_and_Institution */

/*     N.J. Bachman  (JPL) */
/*     L.S. Elson    (JPL) */
/*     E.D. Wright   (JPL) */

/* $ Version */

/* -    SPICELIB Version 1.0.0  15-APR-2009 (NJB) (LSE) (EDW) */

/* -& */
/* $ Index_Entries */

/*     GF ray in instrument FOV search */

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

/*     None. */

/* -& */

/*     SPICELIB functions */


/*     External routines */


/*     Interrupt handler: */


/*     Routines to set step size, refine transition times */
/*     and report work: */


/*     Local parameters */


/*     Geometric quantity  bail switch: */


/*     Progress report switch: */


/*     Local variables */


/*     Standard SPICE error handling. */

    if (return_()) {
	return 0;
    }
    chkin_("GFRFOV", (ftnlen)6);

/*     Note to maintenance programmer: input exception checks */
/*     are delegated to GFFOVE. If the implementation of that */
/*     routine changes, or if this routine is modified to call */
/*     a different routine in place of GFFOVE, then the error */
/*     handling performed by GFFOVE will have to be performed */
/*     here or in a routine called by this routine. */

/*     Check the result window's size. */

    if (sized_(result) < 2) {
	setmsg_("Result window size must be at least 2 but was #.", (ftnlen)
		48);
	i__1 = sized_(result);
	errint_("#", &i__1, (ftnlen)1);
	sigerr_("SPICE(WINDOWTOOSMALL)", (ftnlen)21);
	chkout_("GFRFOV", (ftnlen)6);
	return 0;
    }

/*     Check step size. */

    if (*step <= 0.) {
	setmsg_("Step size must be positive but was #.", (ftnlen)37);
	errdp_("#", step, (ftnlen)1);
	sigerr_("SPICE(INVALIDSTEP)", (ftnlen)18);
	chkout_("GFRFOV", (ftnlen)6);
	return 0;
    }

/*     Set the step size. */

    gfsstp_(step);

/*     Look for solutions. */

    gffove_(inst, "RAY", raydir, " ", rframe, abcorr, obsrvr, &c_b13, (U_fp)
	    gfstep_, (U_fp)gfrefn_, &c_false, (U_fp)gfrepi_, (U_fp)gfrepu_, (
	    U_fp)gfrepf_, &c_false, (L_fp)gfbail_, cnfine, result, inst_len, (
	    ftnlen)3, (ftnlen)1, rframe_len, abcorr_len, obsrvr_len);
    chkout_("GFRFOV", (ftnlen)6);
    return 0;
} /* gfrfov_ */

