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Index Page gfstol_c

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Procedure Abstract Required_Reading Keywords Brief_I/O Detailed_Input | Detailed_Output Parameters Exceptions Files Particulars Examples | Restrictions Literature_References Author_and_Institution Version Index_Entries

#### Procedure

       gfstol_c ( GF, set a tolerance value for GF )

       void gfstol_c ( SpiceDouble value )

#### Abstract

       Override the default GF convergence value used in the high
       level GF routines.

#### Required_Reading

       GF

#### Keywords

       GEOMETRY

#### Brief_I/O

       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       value      I   Double precision value returned or to store.

#### Detailed_Input

       value       is the scalar double precision value to use as the GF subsystem
                   convergence tolerance. This value will override the default
                   tolerance, SPICE_GF_CNVTOL, defined in SpiceGF.h Units are
                   TDB seconds.

#### Detailed_Output

       None.

#### Parameters

       None.

#### Exceptions

       1)  If `value' is not strictly greater-than-zero, the error
           SPICE(INVALIDTOLERANCE) is signaled by a routine in the call
           tree of this routine.

#### Files

       None.

#### Particulars

       The high level GF routines (see gf.req for a listing) use a
       default value for the convergence tolerance, SPICE_GF_CNVTOL,
       defined in SpiceGF.h. It may occur that a GF search run needs a
       different convergence tolerance. gfstol_c programmatically changes
       the tolerance used by those routines.

#### 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) In 14 A.D., the Roman princeps Tiberius sent his son Drusus to subdue
          a revolt of a Roman Legion stationed in Pannonia. A Lunar eclipse
          occurred during this mission.

          Perform a search for occultation events of the sun by earth as
          observed from the Moon center. Search during the interval from
          14 A.D. SEP 1 to 14 A.D. SEP 30 (Julian).

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

             KPL/MK

             File name: gfstol_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
                ---------                     --------
                de408.bsp                     Planetary ephemeris covering
                                              year 14 AD
                pck00009.tpc                  Planet orientation and
                                              radii
                naif0009.tls                  Leapseconds

             \begindata

                KERNELS_TO_LOAD = ( 'de408.bsp',
                                    'pck00009.tpc',
                                    'naif0009.tls'  )

             \begintext

             End of meta-kernel

          Example code begins here.

          /.
             Program gfstol_ex1
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          int main()
             {
             /.
             Local constants
             ./

             #define TIMFMT          "YYYY ERA MON DD HR:MN:SC.#### ::JCAL"
             #define MAXWIN          200
             #define TIMLEN          41

             /.
             Local variables
             ./
             SPICEDOUBLE_CELL      ( cnfine, MAXWIN );
             SPICEDOUBLE_CELL      ( result, MAXWIN );

             SpiceChar             * win0;
             SpiceChar             * win1;
             SpiceChar               begstr [ TIMLEN ];
             SpiceChar               endstr [ TIMLEN ];

             SpiceDouble             et0;
             SpiceDouble             et1;
             SpiceDouble             left;
             SpiceDouble             right;
             SpiceDouble             step;

             SpiceInt                i;

             /.
             Load kernels.
             ./
             furnsh_c ( "gfstol_ex1.tm" );

             /.
             Obtain the TDB time bounds of the confinement
             window, which is a single interval in this case.
             ./
             win0 = "14 A.D. SEP 1  00:00:00";
             win1 = "14 A.D. SEP 30 00:00:00";

             str2et_c ( win0, &et0 );
             str2et_c ( win1, &et1 );

             /.
             Insert the time bounds into the confinement
             window.
             ./
             wninsd_c ( et0, et1, &cnfine );

             /.
             Select a 3-minute step. We'll ignore any occultations
             lasting less than 3 minutes.
             ./
             step = 180.0;

             /.
             Perform the search. 'et[0]' and 'et[1]' have values ~-6*10^10,
             SPICE_GF_CNVTOL has value 10^-6, so double precision addition or
             subtraction of 'et[0]' and 'et[1]' with SPICE_GF_CNVTOL returns
             a result indistinguishable from 'et[0]' and 'et[1]'.

             Reduce the GF convergence tolerance by an order of magnitude
             to resolve this condition.
             ./
             gfstol_c( 1.e-5 );

             gfoclt_c ( "any",
                        "earth",   "ellipsoid",  "iau_earth",
                        "sun",     "ellipsoid",  "iau_sun",
                        "lt",      "moon",      step,
                        &cnfine,   &result                 );

             if ( wncard_c(&result) == 0 )
                {
                printf ( "No occultation was found.\n" );
                }
             else
                {
                for ( i = 0;  i < wncard_c(&result); i++ )
                   {
                   /.
                   Fetch and display each occultation interval.
                   ./
                   wnfetd_c ( &result, i, &left, &right );

                   timout_c ( left,  TIMFMT, TIMLEN, begstr );
                   timout_c ( right, TIMFMT, TIMLEN, endstr );

                   printf ( "Interval %d\n"
                            "   Start time: %s\n"
                            "   Stop time:  %s\n",
                            (int)i, begstr, endstr      );
                   }
                }

             return ( 0 );
             }

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

          Interval 0
             Start time:   14 A.D. SEP 27 05:02:02.8250
             Stop time:    14 A.D. SEP 27 09:33:31.6995

#### Restrictions

       None.

#### Literature_References

       None.

#### Author_and_Institution

       J. Diaz del Rio     (ODC Space)
       E.D. Wright         (JPL)

#### Version

       -CSPICE Version 1.0.2, 06-AUG-2021 (JDR)

           Edited the header to comply with NAIF standard.

           Fixed short error message in -Exceptions section.

       -CSPICE Version 1.0.1, 28-JUN-2016 (EDW)

           Edit to header, correct Required Reading entry eliminating ".REQ"
           suffix.

           Edit to Example code, SpiceInts output as ints using
           explicit casting.

       -CSPICE Version 1.0.0, 27-SEP-2010 (EDW)

#### Index_Entries

       change default convergence tolerance for GF routines

#### Link to routine gfstol_c source file gfstol_c.c

    Fri Dec 31 18:41:07 2021