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gftfov

Table of contents
Procedure
Abstract
Required_Reading
Keywords
Declarations
Brief_I/O
Detailed_Input
Detailed_Output
Parameters
Exceptions
Files
Particulars
Examples
Restrictions
Literature_References
Author_and_Institution
Version

Procedure

     GFTFOV ( GF, is target in FOV? )

     SUBROUTINE GFTFOV ( INST,   TARGET, TSHAPE, TFRAME,
    .                    ABCORR, OBSRVR, STEP,   CNFINE, RESULT )

Abstract

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

Required_Reading

     CK
     FRAMES
     GF
     KERNEL
     NAIF_IDS
     PCK
     SPK
     TIME
     WINDOWS

Keywords

     EVENT
     FOV
     GEOMETRY
     INSTRUMENT
     SEARCH
     WINDOW

Declarations

     IMPLICIT NONE

     INCLUDE               'gf.inc'
     INCLUDE               'zzholdd.inc'

     INTEGER               LBCELL
     PARAMETER           ( LBCELL = -5 )

     CHARACTER*(*)         INST
     CHARACTER*(*)         TARGET
     CHARACTER*(*)         TSHAPE
     CHARACTER*(*)         TFRAME
     CHARACTER*(*)         ABCORR
     CHARACTER*(*)         OBSRVR
     DOUBLE PRECISION      STEP
     DOUBLE PRECISION      CNFINE ( LBCELL : * )
     DOUBLE PRECISION      RESULT ( LBCELL : * )

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.
     TARGET     I   Name of the target body.
     TSHAPE     I   Type of shape model used for target body.
     TFRAME     I   Body-fixed, body-centered frame for target body.
     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    I-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 a target intersection
              search: times when the specified target intersects the
              region of space corresponding to 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.

     TARGET   is the name of the target body, the appearances of
              which in the specified instrument's field of view are
              sought. The body must be an ephemeris object.

              Optionally, you may supply the integer NAIF ID code
              for the body as a string. For example both 'MOON' and
              '301' are legitimate strings that designate the Moon.

              Case and leading or trailing blanks are not
              significant in the string TARGET.

     TSHAPE   is a string indicating the geometric model used to
              represent the shape of the target body. The supported
              options are:

                 'ELLIPSOID'     Use a triaxial ellipsoid model,
                                 with radius values provided via the
                                 kernel pool. A kernel variable
                                 having a name of the form

                                    BODYnnn_RADII

                                 where nnn represents the NAIF
                                 integer code associated with the
                                 body, must be present in the kernel
                                 pool. This variable must be
                                 associated with three numeric
                                 values giving the lengths of the
                                 ellipsoid's X, Y, and Z semi-axes.

                 'POINT'         Treat the body as a single point.

              Case and leading or trailing blanks are not
              significant in the string TSHAPE.

     TFRAME   is the name of the body-fixed, body-centered reference
              frame associated with the target body. Examples of
              such names are 'IAU_SATURN' (for Saturn) and 'ITRF93'
              (for the Earth).

              If the target body is modeled as a point, TFRAME
              is ignored and should be left blank.

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

     ABCORR   indicates the aberration corrections to be applied
              when computing the target's position and orientation.

              For remote sensing applications, where the apparent
              position and orientation of the target seen by the
              observer are desired, normally either of the
              corrections

                 'LT+S'
                 'CN+S'

              should be used. These and the other supported options
              are described below.

              Supported aberration correction options for
              observation (the case where radiation is received by
              observer at ET) are:

                 'NONE'         No correction.

                 'LT'           Light time only

                 'LT+S'         Light time and stellar aberration.

                 'CN'           Converged Newtonian (CN) light time.

                 'CN+S'         CN light time and stellar aberration.

              Supported aberration correction options for
              transmission (the case where radiation is emitted from
              observer at ET) are:

                 'XLT'          Light time only.

                 'XLT+S'        Light time and stellar aberration.

                 'XCN'          Converged Newtonian (CN) light time.

                 'XCN+S'        CN light time and stellar aberration.

              For detailed information, see the GF 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 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.

     RESULT   is a double precision SPICE window which will contain
              the search results. RESULT must be declared and
              initialized with sufficient size to capture the full
              set of time intervals within the search region on which
              the specified condition is satisfied.

              RESULT must be initialized by the caller via the
              SPICELIB routine SSIZED.

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

Detailed_Output

     RESULT   is a SPICE window representing the set of time intervals,
              within the confinement period, when the target body is
              visible; that is, when the target body intersects 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 no times within the confinement window satisfy the
              search criteria, RESULT will be returned with a
              cardinality of zero.

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, an error is signaled by a
         routine in the call tree of this routine.

     2)  Due to numerical errors, in particular,

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

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

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

     3)  If the name of either the target or observer cannot be
         translated to a NAIF ID code, an error is signaled by
         a routine in the call tree of this routine.

     4)  If the specified aberration correction is an unrecognized
         value, an error is signaled by a routine
         in the call tree of this routine.

     5)  If the radii of a target body modeled as an ellipsoid cannot
         be determined by searching the kernel pool for a kernel
         variable having a name of the form

            'BODYnnn_RADII'

         where nnn represents the NAIF integer code associated with
         the body, an error is signaled by a routine in the
         call tree of this routine.

     6)  If the target body coincides with the observer body OBSRVR, an
         error is signaled by a routine in the call tree of this
         routine.

     7)  If the body model specifier TSHAPE is invalid, an error is
         signaled by either this routine or a routine in the call tree
         of this routine.

     8)  If a target body-fixed reference frame associated with a
         non-point target is not recognized, an error is signaled by a
         routine in the call tree of this routine.

     9)  If a target body-fixed reference frame is not centered at the
         corresponding target body, an error is signaled by a routine
         in the call tree of this routine.

     10) If the instrument name INST does not have corresponding NAIF
         ID code, an error is signaled by a routine in the call
         tree of this routine.

     11) If the FOV parameters of the instrument are not present in
         the kernel pool, an error is signaled by a routine
         in the call tree of this routine.

     12) If the FOV boundary has more than MAXVRT vertices, an error
         is signaled by a routine in the call tree of this
         routine.

     13) 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, an error is signaled
         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.

     14) If the loaded kernels provide insufficient data to compute a
         requested state vector, an error is signaled by a
         routine in the call tree of this routine.

     15) If an error occurs while reading an SPK or other kernel file,
         the error is signaled by a routine in the call tree
         of this routine.

     16) If the output SPICE window RESULT has size less than 2, the
         error SPICE(WINDOWTOOSMALL) is signaled.

     17) If the output SPICE window RESULT has insufficient capacity
         to contain the number of intervals on which the specified
         visibility condition is met, an error is signaled
         by a routine in the call tree of 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 target and observer that
        describes the ephemeris of these objects for the period
        defined by the confinement window, CNFINE must be
        loaded. If aberration corrections are used, the states of
        target and observer relative to the solar system barycenter
        must be calculable from the available ephemeris data.
        Typically ephemeris data are made available by loading one
        or more SPK files via FURNSH.

     -  Frame data: if a frame definition is required to convert
        the observer and target states to the body-fixed frame of
        the target, that definition must be available in the kernel
        pool. Typically the definitions of frames not already
        built-in to SPICE are supplied by loading a frame kernel.

        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:

     -  PCK data: bodies modeled as triaxial ellipsoids must have
        orientation data provided by variables in the kernel pool.
        Typically these data are made available by loading a text
        PCK file via FURNSH.

        Bodies modeled as triaxial ellipsoids must have semi-axis
        lengths provided by variables in the kernel pool. Typically
        these data are made available by loading a text PCK file via
        FURNSH.

     -  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 both J2000 and the target
        body-fixed 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).

     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
     within the confinement window when any portion of a specified
     target body appears 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.

     To treat the target as a ray rather than as an ephemeris object,
     use either the higher-level SPICELIB routine GFRFOV or GFFOVE.
     Those routines may be used to search for times when distant
     target objects such as stars are visible in an instrument FOV, as
     long the direction from the observer to the target can be modeled
     as a ray.

     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 target body
     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 target and
     observer can be a valuable aid in picking a reasonable step size.
     In general, the user can compensate for lack of such knowledge by
     picking a very short step size; the cost is increased computation
     time.

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


     Convergence Tolerance
     =====================

     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 default convergence tolerance
     used by this routine is set by the parameter CNVTOL (defined
     in gf.inc).

     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.

     The user may change the convergence tolerance from the default
     CNVTOL value by calling the routine GFSTOL, e.g.

        CALL GFSTOL( tolerance value )

     Call GFSTOL prior to calling this routine. All subsequent
     searches will use the updated tolerance value.

     Setting 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 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) 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.

        Use the meta-kernel shown below to load the required SPICE
        kernels.


           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
              -----------------------------   ----------------------
              naif0012.tls                    Leapseconds
              pck00010.tpc                    Satellite orientation
                                              and radii
              041014R_SCPSE_01066_04199.bsp   CASSINI, planetary and
                                              Saturn satellite
                                              ephemeris
              cas_v40.tf                      Cassini FK
              04161_04164ra.bc                Cassini bus CK
              cas00071.tsc                    Cassini SCLK kernel
              cas_iss_v10.ti                  Cassini IK


           \begindata

              KERNELS_TO_LOAD = ( 'naif0012.tls',
                                  'pck00010.tpc',
                                  '041014R_SCPSE_01066_04199.bsp',
                                  'cas_v40.tf',
                                  '04161_04164ra.bc',
                                  'cas00071.tsc',
                                  'cas_iss_v10.ti'            )
           \begintext

           End of meta-kernel


        Example code begins here.


              PROGRAM GFTFOV_EX1
              IMPLICIT NONE

        C
        C     SPICELIB functions
        C
              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' )

              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               SHPLEN
              PARAMETER           ( SHPLEN = 25 )

              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*(BDNMLN)    TARGET
              CHARACTER*(FRNMLN)    TFRAME
              CHARACTER*(TIMLEN)    TIMSTR ( 2 )
              CHARACTER*(SHPLEN)    TSHAPE

              DOUBLE PRECISION      CNFINE ( LBCELL : 2 )
              DOUBLE PRECISION      ENDPT  ( 2 )
              DOUBLE PRECISION      ET0
              DOUBLE PRECISION      ET1
              DOUBLE PRECISION      RESULT ( LBCELL : MAXWIN )
              DOUBLE PRECISION      STEPSZ

              INTEGER               I
              INTEGER               J
              INTEGER               N

        C
        C     Saved variables
        C
        C     The confinement and result windows CNFINE and RESULT are
        C     saved because this practice helps to prevent stack
        C     overflow.
        C
              SAVE                  CNFINE
              SAVE                  RESULT

        C
        C     Load kernels.
        C
              CALL FURNSH ( META )

        C
        C     Initialize windows.
        C
              CALL SSIZED ( 2,      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_NAC'
              TARGET = 'PHOEBE'
              TSHAPE = 'ELLIPSOID'
              TFRAME = 'IAU_PHOEBE'
              ABCORR = 'LT+S'
              OBSRVR = 'CASSINI'
              STEPSZ = 10.D0

              WRITE (*,*) ' '
              WRITE (*,*) 'Instrument: '//INST
              WRITE (*,*) 'Target:     '//TARGET
              WRITE (*,*) ' '

        C
        C     Perform the search.
        C
              CALL GFTFOV ( INST,   TARGET, TSHAPE, TFRAME,
             .              ABCORR, OBSRVR, STEPSZ, CNFINE, RESULT )

              N = WNCARD( RESULT )

              IF ( N .EQ. 0 ) THEN

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

              ELSE

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

                 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(34:) = TIMSTR(2)

                    WRITE (*,*) LINE

                 END DO

              END IF

              WRITE (*,*) ' '
              END


        When this program was executed on a Mac/Intel/gfortran/64-bit
        platform, the output was:


         Instrument: CASSINI_ISS_NAC
         Target:     PHOEBE

          Visibility start time (TDB)           Stop time (TDB)
          ---------------------------     ---------------------------
          2004-JUN-11 07:35:27.066980     2004-JUN-11 08:48:03.954696
          2004-JUN-11 09:02:56.580045     2004-JUN-11 09:35:04.038509
          2004-JUN-11 09:49:56.476397     2004-JUN-11 10:22:04.242879
          2004-JUN-11 10:36:56.283772     2004-JUN-11 11:09:04.397165
          2004-JUN-11 11:23:56.020645     2004-JUN-11 11:56:04.733535

Restrictions

     1)  The reference frame associated with INST must be
         centered at the observer or must be inertial. No check is done
         to ensure this.

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

Literature_References

     None.

Author_and_Institution

     N.J. Bachman       (JPL)
     J. Diaz del Rio    (ODC Space)
     L.S. Elson         (JPL)
     E.D. Wright        (JPL)

Version

    SPICELIB Version 1.1.1, 06-AUG-2021 (JDR)

        Edited the header to comply with NAIF standard.

        Modified code example's output to comply with maximum line
        length of header comments. Updated Example's kernels set to use
        PDS archived data. Added SAVE statements for CNFINE and RESULT
        variables in code example.

        Updated description of RESULT argument in $Brief_I/O,
        $Detailed_Input and $Detailed_Output.

    SPICELIB Version 1.1.0, 28-FEB-2012 (EDW)

        Implemented use of ZZHOLDD to allow user to alter convergence
        tolerance.

        Removed the STEP > 0 error check. The GFSSTP call includes
        the check.

    SPICELIB Version 1.0.0, 15-APR-2009 (NJB) (LSE) (EDW)
Fri Dec 31 18:36:25 2021