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Index Page gfsep_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

       gfsep_c (GF, angular separation search)

       void gfsep_c (  ConstSpiceChar     * targ1,
                       ConstSpiceChar     * shape1,
                       ConstSpiceChar     * frame1,
                       ConstSpiceChar     * targ2,
                       ConstSpiceChar     * shape2,
                       ConstSpiceChar     * frame2,
                       ConstSpiceChar     * abcorr,
                       ConstSpiceChar     * obsrvr,
                       ConstSpiceChar     * relate,
                       SpiceDouble          refval,
                       SpiceDouble          adjust,
                       SpiceDouble          step,
                       SpiceInt             nintvls,
                       SpiceCell          * cnfine,
                       SpiceCell          * result  )

#### Abstract

       Determine time intervals when the angular separation between
       the position vectors of two target bodies relative to an observer
       satisfies a numerical relationship.

#### Required_Reading

       GF
       NAIF_IDS
       SPK
       TIME
       WINDOWS

#### Keywords

       EVENT
       GEOMETRY
       SEARCH
       SEPARATION

#### Brief_I/O

       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       SPICE_GF_CNVTOL
                  P   Convergence tolerance.
       targ1      I   Name of first body.
       shape1     I   Name of shape model describing the first body.
       frame1     I   The body-fixed reference frame of the first body.
       targ2      I   Name of second body.
       shape2     I   Name of the shape model describing the second body.
       frame2     I   The body-fixed reference frame of the second body.
       abcorr     I   Aberration correction flag.
       obsrvr     I   Name of the observing body.
       relate     I   Operator that either looks for an extreme value
                      (max, min, local, absolute) or compares the
                      angular separation value and `refval'.
       refval     I   Reference value.
       adjust     I   Absolute extremum adjustment value.
       step       I   Step size in seconds for finding angular separation
                      events.
       nintvls    I   Workspace window interval count.
       cnfine    I-O  SPICE window to which the search is restricted.
       result     O   SPICE window containing results.

#### Detailed_Input

       targ1       is the string naming the first body of interest. You can
                   also supply the integer ID code for the object as an
                   integer string. For example both "MOON" and "301"
                   are legitimate strings that indicate the moon is the
                   target body.

       shape1      is the string naming the geometric model used to
                   represent the shape of the `targ1' body. Models supported
                   by this routine:

                      "SPHERE"   Treat the body as a sphere with radius
                                 equal to the maximum value of
                                 BODYnnn_RADII.

                      "POINT"    Treat the body as a point; radius has value
                                 zero.

                   The `shape1' string lacks sensitivity to case, leading
                   and trailing blanks.

       frame1      is the string naming the body-fixed reference frame
                   corresponding to `targ1'. gfsep_c does not currently use
                   this argument's value, its use is reserved for future
                   shape models. The value "NULL" will suffice for
                   "POINT" and "SPHERE" shaped bodies.

       targ2       is the string naming the second body of interest. You can
                   also supply the integer ID code for the object as an
                   integer string. For example both "MOON" and "301"
                   are legitimate strings that indicate the moon is the
                   target body.

       shape2      is the string naming the geometric model used to
                   represent the shape of the `targ2'. Models supported by
                   this routine:

                      "SPHERE"   Treat the body as a sphere with radius
                                 equal to the maximum value of
                                 BODYnnn_RADII.

                      "POINT"    Treat the body as a single point; radius
                                 has value zero.

                   The `shape2' string lacks sensitivity to case, leading
                   and trailing blanks.

       frame2      is the string naming the body-fixed reference frame
                   corresponding to `targ2'. gfsep_c does not currently use
                   this argument's value, its use is reserved for future
                   shape models. The value "NULL" will suffice for
                   "POINT" and "SPHERE" shaped bodies.

       abcorr      is the string description of the aberration corrections
                   to apply to the state evaluations to account for
                   one-way light time and stellar aberration.

                   This routine accepts the same aberration corrections
                   as does the SPICE routine spkezr_c. See the header of
                   spkezr_c for a detailed description of the aberration
                   correction options. For convenience, the options are
                   listed below:

                      "NONE"     Apply no correction.

                      "LT"       "Reception" case: correct for
                                 one-way light time using a Newtonian
                                 formulation.

                      "LT+S"     "Reception" case: correct for
                                 one-way light time and stellar
                                 aberration using a Newtonian
                                 formulation.

                      "CN"       "Reception" case: converged
                                 Newtonian light time correction.

                      "CN+S"     "Reception" case: converged
                                 Newtonian light time and stellar
                                 aberration corrections.

                      "XLT"      "Transmission" case: correct for
                                 one-way light time using a Newtonian
                                 formulation.

                      "XLT+S"    "Transmission" case: correct for
                                 one-way light time and stellar
                                 aberration using a Newtonian
                                 formulation.

                      "XCN"      "Transmission" case: converged
                                 Newtonian light time correction.

                      "XCN+S"    "Transmission" case: converged
                                 Newtonian light time and stellar
                                 aberration corrections.

                   The `abcorr' string lacks sensitivity to case, leading
                   and trailing blanks.

       obsrvr      is the string naming the observing body. Optionally, you
                   may supply the ID code of the object as an integer
                   string. For example, both "EARTH" and "399" are
                   legitimate strings to supply to indicate the
                   observer is Earth.

       relate      is the string identifying the relational operator used to
                   define a constraint on the angular separation. The
                   result window found by this routine indicates the time
                   intervals where the constraint is satisfied. Supported
                   values of `relate' and corresponding meanings are shown
                   below:

                      ">"       Separation is greater than the reference
                                value `refval'.

                      "="       Separation is equal to the reference
                                value `refval'.

                      "<"       Separation is less than the reference
                                value `refval'.

                     "ABSMAX"   Separation is at an absolute maximum.

                     "ABSMIN"   Separation is at an absolute  minimum.

                     "LOCMAX"   Separation is at a local maximum.

                     "LOCMIN"   Separation is at a local minimum.

                   The caller may indicate that the region of interest
                   is the set of time intervals where the quantity is
                   within a specified angular separation of an absolute
                   extremum. The argument `adjust' (described below) is used
                   to specify this angular separation.

                   Local extrema are considered to exist only in the
                   interiors of the intervals comprising the confinement
                   window:  a local extremum cannot exist at a boundary
                   point of the confinement window.

                   The `relate' string lacks sensitivity to case, leading
                   and trailing blanks.

       refval      is the double precision reference value used together
                   with `relate' argument to define an equality or inequality
                   to be satisfied by the angular separation between the
                   specified target and observer. See the discussion of
                   `relate' above for further information.

                   The units of `refval' are radians.

       adjust      is a double precision value used to modify searches for
                   absolute extrema: when `relate' is set to "ABSMAX" or
                   "ABSMIN" and `adjust' is set to a positive value, gfsep_c
                   finds times when the angular separation between the
                   bodies is within `adjust' radians of the specified
                   extreme value.

                   For `relate' set to "ABSMAX", the `result' window contains
                   time intervals when the angular separation has
                   values between absmax - adjust and `absmax'.

                   For `relate' set to "ABSMIN", the `result' window contains
                   time intervals when the angular separation has
                   values between `absmin' and absmin + adjust.

                   `adjust' is not used for searches for local extrema,
                   equality or inequality conditions.

       step        is the double precision time step size to use in the
                   search.

                   `step' must be short enough to for a search using this
                   step size to locate the time intervals where the
                   specified angular separation function is monotone
                   increasing or decreasing. 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 SPICE_GF_CNVTOL for
                   details.

                   `step' has units of TDB seconds.

       nintvls     is an integer parameter specifying the number of intervals
                   that can be accommodated by each of the dynamically allocated
                   workspace windows used internally by this routine.

                   In many cases, it's not necessary to compute an accurate
                   estimate of how many intervals are needed; rather, the user
                   can pick a size considerably larger than what's really
                   required.

                   However, since excessively large arrays can prevent
                   applications from compiling, linking, or running properly,
                   sometimes `nintvls' must be set according to the actual
                   workspace requirement. A rule of thumb for the number of
                   intervals needed is

                      nintvls  =  2*n  +  ( m / step )

                   where

                      n      is the number of intervals in the confinement
                             window.

                      m      is the measure of the confinement window, in units
                             of seconds.

                      step   is the search step size in seconds.

       cnfine      is a double precision 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.

                   In some cases the confinement window can be used to
                   greatly reduce the time period that must be searched
                   for the desired solution. See the -Particulars section
                   below for further discussion.

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

                   In some cases the observer's state may be computed at
                   times outside of `cnfine' by as much as 2 seconds. See
                   -Particulars for details.

                   `cnfine' must be declared as a double precision SpiceCell.

                   CSPICE provides the following macro, which declares and
                   initializes the cell

                      SPICEDOUBLE_CELL        ( cnfine, CNFINESZ );

                   where CNFINESZ is the maximum capacity of `cnfine'.

#### Detailed_Output

       cnfine      is the input confinement window, updated if necessary so the
                   control area of its data array indicates the window's size
                   and cardinality. The window data are unchanged.

       result      is the SPICE window of intervals, contained within the
                   confinement window `cnfine', on which the specified
                   constraint is satisfied.

                   `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.

                   If `result' is non-empty on input, its contents will be
                   discarded before gfsep_c conducts its search.

                   The endpoints of the time intervals comprising `result' are
                   interpreted as seconds past J2000 TDB.

                   If the search is for local extrema, or for absolute
                   extrema with `adjust' set to zero, then normally each
                   interval of `result' will be a singleton: the left and
                   right endpoints of each interval will be identical.

                   If no times within the confinement window satisfy the
                   search criteria, `result' will be returned with a
                   cardinality of zero.

                   `result' must be declared as a double precision SpiceCell.

                   CSPICE provides the following macro, which declares and
                   initializes the cell

                      SPICEDOUBLE_CELL        ( result, RESULTSZ );

                   where RESULTSZ is the maximum capacity of `result'.

#### Parameters

       SPICE_GF_CNVTOL

                  is the convergence tolerance used for finding endpoints
                  of the intervals comprising the result window.
                  SPICE_GF_CNVTOL is used to determine when binary searches
                  for roots should terminate: when a root is bracketed
                  within an interval of length SPICE_GF_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.

                  SPICE_GF_CNVTOL has the value 1.0e-6. Units are TDB
                  seconds.

#### 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. One technique to handle such a situation,
           slightly contract `result' using the window routine wncond_c.

       3)  If the number of intervals `nintvls' is less than 1, the error
           SPICE(VALUEOUTOFRANGE) is signaled.

       4)  If result window, `result', is not at least 2 and an even value,
           the error SPICE(INVALIDDIMENSION) is signaled by a routine in
           the call tree of this routine.

       5)  If `result' has insufficient capacity to contain the
           number of intervals on which the specified distance condition
           is met, an error is signaled by a routine in the call
           tree of this routine.

       6)  If an error (typically cell overflow) occurs during
           window arithmetic, the error is signaled by a routine
           in the call tree of this routine.

       7)  If the relational operator `relate' is not recognized, an
           error is signaled by a routine in the call tree of this
           routine.

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

       9)  If `adjust' is negative, an error is signaled by a routine in
           the call tree of this routine.

       10) If either of the input body names, `targ1', `targ2' do not map
           to NAIF ID codes, an error is signaled by a routine in the
           call tree of this routine.

       11) If either of the input body shape names, `shape1', `shape2',
           are not recognized by the GF subsystem, an error is signaled
           by a routine in the call tree of this routine.

       12) If either of the input body frame names, `frame1', `frame2',
           are not recognized by the frame subsystem, an error is
           signaled by a routine in the call tree of this routine.

       13) If either of the input body frames, `frame1', `frame2',
           are not centered on the corresponding body (`frame1' on `targ1',
           `frame2' on `targ2'), an error is signaled by a routine in the
           call tree of this routine.

       14) If required ephemerides or other kernel data are not
           available, an error is signaled by a routine in the call tree
           of this routine.

       15) If any of the `targ1', `shape1', `frame1', `targ2', `shape2',
           `frame2', `abcorr', `obsrvr' or `relate' input string pointers
           is null, the error SPICE(NULLPOINTER) is signaled.

       16) If any of the `targ1', `shape1', `frame1', `targ2', `shape2',
           `frame2', `abcorr', `obsrvr' or `relate' input strings has
           zero length, the error SPICE(EMPTYSTRING) is signaled.

       17) If any the `cnfine' or `result' cell arguments has a type
           other than SpiceDouble, the error SPICE(TYPEMISMATCH) is
           signaled.

       18) If memory cannot be allocated to create the temporary variable
           required for the execution of the underlying Fortran routine,
           the error SPICE(MALLOCFAILED) is signaled.

#### Files

       Appropriate SPK and PCK kernels must be loaded by the
       calling program before this routine is called.

       The following data are required:

       -  SPK data: the calling application must load ephemeris data
          for the targets, observer, and any intermediate objects in
          a chain connecting the targets and observer that cover the
          time period specified by the window `cnfine'. 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 using
          furnsh_c.

       -  PCK data: 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 using furnsh_c.

       -  If non-inertial reference frames are used, then PCK
          files, frame kernels, C-kernels, and SCLK kernels may be
          needed.

       -  In some cases the observer's state may be computed at times
          outside of `cnfine' by as much as 2 seconds; data required to
          compute this state must be provided by loaded kernels. See
          -Particulars for details.

       Such kernel data are normally loaded once per program
       run, NOT every time this routine is called.

#### Particulars

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

       This routine determines a set of one or more time intervals
       within the confinement window for which the angular separation
       between the two bodies satisfies some defined relationship.
       The resulting set of intervals is returned as a SPICE window.

       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
       ==================

       Regardless of the type of constraint selected by the caller, this
       routine starts the search for solutions by determining the time
       periods, within the confinement window, over which the specified
       angular separation function is monotone increasing and monotone
       decreasing. Each of these time periods is represented by a SPICE
       window. Having found these windows, all of the angular separation
       function's local extrema within the confinement window are known.
       Absolute extrema then can be found very easily.

       Within any interval of these "monotone" windows, there will be at
       most one solution of any equality constraint. Since the boundary
       of the solution set for any inequality constraint is contained in
       the union of

       -  the set of points where an equality constraint is met

       -  the boundary points of the confinement window

       the solutions of both equality and inequality constraints can be
       found easily once the monotone windows have been found.

       Step Size
       =========

       The monotone windows (described above) are found using a two-step
       search process. 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 sign of the rate of
       change of angular separation (angular separation rate) will be
       sampled. Starting at the left endpoint of an interval, samples
       will be taken at each step. If a change of sign is found, a
       root has been bracketed; at that point, the time at which the
       angular separation rate is zero can be found by a refinement
       process, for example, using a binary search.

       Note that the optimal choice of step size depends on the lengths
       of the intervals over which the distance function is monotone:
       the step size should be shorter than the shortest of these
       intervals (within the confinement window).

       The optimal step size is *not* necessarily related to the lengths
       of the intervals comprising the result window. For example, if
       the shortest monotone interval has length 10 days, and if the
       shortest result window interval has length 5 minutes, a step size
       of 9.9 days is still adequate to find all of the intervals in the
       result window. In situations like this, the technique of using
       monotone windows yields a dramatic efficiency improvement over a
       state-based search that simply tests at each step whether the
       specified constraint is satisfied. The latter type of search can
       miss solution intervals if the step size is longer than the
       shortest solution interval.

       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
       =====================

       As described above, the root-finding process used by this routine
       involves first bracketing roots and then using a search process
       to locate them. "Roots" are both times when local extrema are
       attained and times when the distance function is equal to a
       reference value. All endpoints of the intervals comprising the
       result window are either endpoints of intervals of the
       confinement window or roots.

       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 SPICE_GF_CNVTOL (defined
       in SpiceGF.h).

       The value of SPICE_GF_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
       SPICE_GF_CNVTOL value by calling the routine gfstol_c, e.g.

          gfstol_c ( tolerance value );

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

       Setting the tolerance tighter than SPICE_GF_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.

       Certain types of searches require the state of the observer,
       relative to the solar system barycenter, to be computed at times
       slightly outside the confinement window `cnfine'. The time window
       that is actually used is the result of "expanding" `cnfine' by a
       specified amount "T": each time interval of `cnfine' is expanded by
       shifting the interval's left endpoint to the left and the right
       endpoint to the right by T seconds. Any overlapping intervals are
       merged. (The input argument `cnfine' is not modified.)

       The window expansions listed below are additive: if both
       conditions apply, the window expansion amount is the sum of the
       individual amounts.

       -  If a search uses an equality constraint, the time window
          over which the state of the observer is computed is expanded
          by 1 second at both ends of all of the time intervals
          comprising the window over which the search is conducted.

       -  If a search uses stellar aberration corrections, the time
          window over which the state of the observer is computed is
          expanded as described above.

       When light time corrections are used, expansion of the search
       window also affects the set of times at which the light time-
       corrected state of the target is computed.

       In addition to the possible 2 second expansion of the search
       window that occurs when both an equality constraint and stellar
       aberration corrections are used, round-off error should be taken
       into account when the need for data availability is analyzed.

       Negative Angular Separation
       ===========================

       For those searches using a SPHERE shape identifier for both
       target bodies, the angular separation function returns a
       negative value when the bodies overlap (occult), e.g.
       a search for an ABSMIN of angular separation in a
       confinement window covering an occultation event will
       return the time when the apparent center of the
       occulting body passes closest to the apparent center of
       the occulted body.

       Elongation
       ===========================

       The angular separation of two targets as seen from an observer
       where one of those targets is the sun is known as elongation.

#### 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) Determine the times of local maxima of the angular separation
          between the moon and earth as observed from the sun from
          January 1, 2007 UTC to July 1, 2007 UTC.

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

             KPL/MK

             File name: gfsep_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
                ---------                     --------
                de421.bsp                     Planetary ephemeris
                pck00009.tpc                  Planet orientation and
                                              radii
                naif0009.tls                  Leapseconds

             \begindata

                KERNELS_TO_LOAD = ( 'de421.bsp',
                                    'pck00009.tpc',
                                    'naif0009.tls'  )

             \begintext

             End of meta-kernel

          Example code begins here.

          /.
             Program gfsep_ex1
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          int main( )
             {

             #define BODYLN    21
             #define MAXWIN    1000
             #define TIMFMT    "YYYY-MON-DD HR:MN:SC.###### (TDB) ::TDB ::RND"
             #define TIMLEN    41

             /.
             Create the needed windows. Note, one window
             consists of two values, so the total number
             of cell values to allocate equals twice
             the number of windows.
             ./
             SPICEDOUBLE_CELL ( result, 2*MAXWIN );
             SPICEDOUBLE_CELL ( cnfine, 2       );

             SpiceDouble       begtim;
             SpiceDouble       endtim;
             SpiceDouble       step;
             SpiceDouble       adjust;
             SpiceDouble       refval;
             SpiceDouble       beg;
             SpiceDouble       end;

             SpiceChar         begstr [ TIMLEN ];
             SpiceChar         endstr [ TIMLEN ];

             SpiceChar         targ1  [ BODYLN ];
             SpiceChar         targ2  [ BODYLN ];
             SpiceChar         obsrvr [ BODYLN ];

             SpiceChar       * frame1 = "NULL";
             SpiceChar       * shape1 = "SPHERE";

             SpiceChar       * frame2 = "NULL";
             SpiceChar       * shape2 = "SPHERE";

             SpiceChar       * abcorr = "NONE";
             SpiceChar       * relate = "LOCMAX";

             SpiceInt          count;
             SpiceInt          i;

             /.
             Load kernels.
             ./
             furnsh_c( "gfsep_ex1.tm" );

             /.
             Store the time bounds of our search interval in
             the cnfine confinement window.
             ./
             str2et_c( "2007 JAN 01", &begtim );
             str2et_c( "2007 JUL 01", &endtim );

             wninsd_c ( begtim, endtim, &cnfine );

             /.
             Prompt for the inputs.
             ./
             prompt_c ( "First body     > ", BODYLN, targ1  );
             prompt_c ( "Second body    > ", BODYLN, targ2  );
             prompt_c ( "Observing body > ", BODYLN, obsrvr );

             /.
             Search using a step size of 6 days (in units of seconds).
             ./
             step   = 6.*spd_c();
             adjust = 0.;
             refval = 0.;

             /.
             List the beginning and ending points in each interval
             if result contains data.
             ./
             gfsep_c ( targ1,
                      shape1,
                      frame1,
                      targ2,
                      shape2,
                      frame2,
                      abcorr,
                      obsrvr,
                      relate,
                      refval,
                      adjust,
                      step,
                      MAXWIN,
                      &cnfine,
                      &result );

             count = wncard_c( &result );

             /.
             Display the results.
             ./
             if (count == 0 )
                {
                printf ( "Result window is empty.\n\n" );
                }
             else
                {
                for ( i = 0;  i < count;  i++ )
                   {

                   /.
                   Fetch the endpoints of the Ith interval
                   of the result window.
                   ./
                   wnfetd_c ( &result, i, &beg, &end );

                   timout_c ( beg, TIMFMT, TIMLEN, begstr );
                   timout_c ( end, TIMFMT, TIMLEN, endstr );

                   printf ( "Interval %d\n", i + 1);
                   printf ( "Beginning TDB %s \n", begstr );
                   printf ( "Ending TDB    %s \n", endstr );

                   }
                }

             kclear_c();
             return( 0 );
             }

          When this program was executed on a Mac/Intel/cc/64-bit
          platform, using "MOON" as first body, "EARTH" as second body
          and "SUN" as observing body, the output was:

          First body     > MOON
          Second body    > EARTH
          Observing body > SUN
          Interval 1
          Beginning TDB 2007-JAN-11 11:21:20.214305 (TDB)
          Ending TDB    2007-JAN-11 11:21:20.214305 (TDB)
          Interval 2
          Beginning TDB 2007-JAN-26 01:43:41.027309 (TDB)
          Ending TDB    2007-JAN-26 01:43:41.027309 (TDB)
          Interval 3
          Beginning TDB 2007-FEB-10 04:49:53.431964 (TDB)
          Ending TDB    2007-FEB-10 04:49:53.431964 (TDB)
          Interval 4
          Beginning TDB 2007-FEB-24 13:18:18.953256 (TDB)
          Ending TDB    2007-FEB-24 13:18:18.953256 (TDB)
          Interval 5
          Beginning TDB 2007-MAR-11 20:41:59.571964 (TDB)
          Ending TDB    2007-MAR-11 20:41:59.571964 (TDB)
          Interval 6
          Beginning TDB 2007-MAR-26 01:20:26.860201 (TDB)
          Ending TDB    2007-MAR-26 01:20:26.860201 (TDB)
          Interval 7
          Beginning TDB 2007-APR-10 10:24:39.017514 (TDB)
          Ending TDB    2007-APR-10 10:24:39.017514 (TDB)
          Interval 8
          Beginning TDB 2007-APR-24 14:00:49.422728 (TDB)
          Ending TDB    2007-APR-24 14:00:49.422728 (TDB)
          Interval 9
          Beginning TDB 2007-MAY-09 21:53:25.643532 (TDB)
          Ending TDB    2007-MAY-09 21:53:25.643532 (TDB)
          Interval 10
          Beginning TDB 2007-MAY-24 03:14:05.873982 (TDB)
          Ending TDB    2007-MAY-24 03:14:05.873982 (TDB)
          Interval 11
          Beginning TDB 2007-JUN-08 07:24:13.686616 (TDB)
          Ending TDB    2007-JUN-08 07:24:13.686616 (TDB)
          Interval 12
          Beginning TDB 2007-JUN-22 16:45:56.506850 (TDB)
          Ending TDB    2007-JUN-22 16:45:56.506850 (TDB)

       2) Determine the time of local maxima elongation of the
          Moon as seen from Earth for the same time interval
          as the previous example, i.e. find the local maxima of
          the angular separation between the Moon and the Sun as
          seen from the Earth, by running the code in example #1.

          When Example #1 was executed on a Mac/Intel/cc/64-bit
          platform, using "MOON" as first body, "SUN" as second body
          and "EARTH" as observing body, the output was:

          First body     > MOON
          Second body    > SUN
          Observing body > EARTH
          Interval 1
          Beginning TDB 2007-JAN-03 14:20:24.617627 (TDB)
          Ending TDB    2007-JAN-03 14:20:24.617627 (TDB)
          Interval 2
          Beginning TDB 2007-FEB-02 06:16:24.101517 (TDB)
          Ending TDB    2007-FEB-02 06:16:24.101517 (TDB)
          Interval 3
          Beginning TDB 2007-MAR-03 23:22:41.994972 (TDB)
          Ending TDB    2007-MAR-03 23:22:41.994972 (TDB)
          Interval 4
          Beginning TDB 2007-APR-02 16:49:16.135505 (TDB)
          Ending TDB    2007-APR-02 16:49:16.135505 (TDB)
          Interval 5
          Beginning TDB 2007-MAY-02 09:41:43.830081 (TDB)
          Ending TDB    2007-MAY-02 09:41:43.830081 (TDB)
          Interval 6
          Beginning TDB 2007-JUN-01 01:03:44.527470 (TDB)
          Ending TDB    2007-JUN-01 01:03:44.527470 (TDB)
          Interval 7
          Beginning TDB 2007-JUN-30 14:15:26.576292 (TDB)
          Ending TDB    2007-JUN-30 14:15:26.576292 (TDB)

#### Restrictions

       1)  The kernel files to be used by this routine must be loaded
           (normally via the CSPICE routine furnsh_c) before this routine
           is called.

       2)  This routine has the side effect of re-initializing the
           angular separation quantity utility package. Callers may
           need to re-initialize the package after calling this routine.

       3)  Due to the current logic implemented in zzgfspu, a direct
           search for zero angular separation of two point targets will
           always fails, i.e.,

                'relate' has value "="
                'refval' has value 0.

             Use 'relate' values of "ABSMIN" or "LOCMIN" to detect such an
             event(s).

#### Literature_References

       None.

#### Author_and_Institution

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

#### Version

       -CSPICE Version 1.1.0, 01-NOV-2021 (JDR) (EDW)

           Added use of ALLOC_CHECK_INTRA to check net null effect on
           alloc count.

           Updated header to describe use of expanded confinement window.

           Edited the header to comply with NAIF standard.

           Reduced the search interval to limit the length of the solutions
           and modified the example code to prompt for the required inputs.

           Updated the description of "nintvls", "cnfine" and "result"
           arguments.

           Added entries #4, #5 and #17 in -Exceptions section.

       -CSPICE Version 1.0.2, 30-JUL-2014 (EDW)

           Edit to argument I/O 'frame1' and 'frame2' to mention use of
           "NULL."

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

       -CSPICE Version 1.0.1, 28-FEB-2013 (NJB) (EDW)

           Header was updated to discuss use of gfstol_c.

           Edit to comments to correct search description.

           Edited argument descriptions. Removed mention of "ELLIPSOID"
           shape from 'shape1' and 'shape2' as that option is not yet
           implemented.

           Typo corrected in -Version: entry 1.0.1 updated: replaced
           "gfrr_c" with "gfsep_c."

           Small text edit for clarity on example code description; full date
           strings replaced abbreviated versions.

           Edits to Example section, proper description of "standard.tm"
           meta kernel.

           Edits to -Exceptions section to improve description of
           exceptions and error signals.

       -CSPICE Version 1.0.1, 19-AUG-2009 (EDW)

           Corrected typo in the VALUEOUTOFRANGE error message. Corrected
           the routine name in "chkout_c" call, "gfposc_c", with correct
           name "gfsep_c."

       -CSPICE Version 1.0.0, 10-FEB-2009 (NJB) (EDW)

#### Index_Entries

       GF angular separation search

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

    Fri Dec 31 18:41:07 2021