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cspice_gfsep

Table of contents
Abstract
I/O
Parameters
Examples
Particulars
Exceptions
Files
Restrictions
Required_Reading
Literature_References
Author_and_Institution
Version
Index_Entries

Abstract


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

I/O


   Given:

      targ1    the name of the first body of interest.

               [1,c1] = size(targ1); char = class(targ1)

                  or

               [1,1] = size(targ1); cell = class(targ1)

               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   the name of the geometric model used to represent the shape
               of the `targ1' body.

               [1,c2] = size(shape1); char = class(shape1)

                  or

               [1,1] = size(shape1); cell = class(shape1)

               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   the name of the body-fixed reference frame corresponding
               to `targ1'.

               [1,c3] = size(frame1); char = class(frame1)

                  or

               [1,1] = size(frame1); cell = class(frame1)

               cspice_gfsep 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    the name of the second body of interest.

               [1,c4] = size(targ2); char = class(targ2)

                  or

               [1,1] = size(targ2); cell = class(targ2)

               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   the name of the geometric model used to represent
               the shape of the `targ2'.

               [1,c5] = size(shape2); char = class(shape2)

                  or

               [1,1] = size(shape2); cell = class(shape2)

               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   the name of the body-fixed reference frame corresponding
               to `targ2'.

               [1,c6] = size(frame2); char = class(frame2)

                  or

               [1,1] = size(frame2); cell = class(frame2)

               cspice_gfsep 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   describes the aberration corrections to apply to the state
               evaluations to account for one-way light time and stellar
               aberration.

               [1,c7] = size(abcorr); char = class(abcorr)

                  or

               [1,1] = size(abcorr); cell = class(abcorr)

               This routine accepts the same aberration corrections as does
               the routine cspice_spkezr. See the header of cspice_spkezr
               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, and to
               embedded, leading and trailing blanks.

      obsrvr   the name of the observing body.

               [1,c8] = size(obsrvr); char = class(obsrvr)

                  or

               [1,1] = size(obsrvr); cell = class(obsrvr)

               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   the constraint relational operator on the angular separation.

               [1,c9] = size(relate); char = class(relate)

                  or

               [1,1] = size(relate); cell = class(relate)

               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.

               Negative Angular Separation

                  For those searches using a SPHERE shape identifier for
                  either target body, the angular separation function
                  returns a negative value when the bodies overlap (occult).

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

      refval   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.

               [1,1] = size(refval); double = class(refval)

               See the discussion of `relate' above for further information.

               The units of 'refval' are radians.

      adjust   value used to modify searches for absolute extrema.

               [1,1] = size(adjust); double = class(adjust)

               When `relate' is set to 'ABSMAX' or 'ABSMIN' and `adjust' is
               set to a positive value, cspice_gfsep 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     time step size to use in the search.

               [1,1] = size(step); double = class(step)

               `step' must be short enough for a search using this step size
               to locate the time intervals where coordinate function of the
               observer-target vector 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  value specifying the number of intervals in the internal
               workspace array used by this routine.

               [1,1] = size(nintvls); int32 = class(nintvls)

               `nintvls' should be at least as large as the number of
               intervals within the search region on which the specified
               observer-target vector coordinate function is monotone
               increasing or decreasing. It does no harm to pick a value of
               `nintvls' larger than the minimum required to execute the
               specified search, but if chosen too small, the search will
               fail.

      cnfine   a SPICE window that confines the time period over which the
               specified search is conducted.

               [2m,1] = size(cnfine); double = class(cnfine)

               `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.

   the call:

      [result] = cspice_gfsep( targ1,  shape1, frame1,  targ2,  shape2,   ...
                               frame2, abcorr, obsrvr,  relate, refval,   ...
                               adjust, step,   nintvls, cnfine )

   returns:

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

               [2n,1] = size(result); double = class(result)

               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
               constraint, `result' will return with cardinality zero.

Parameters


   All parameters described here are declared in the Mice include file
   MiceGF.m. See that file for parameter values.

   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.

Examples


   Any numerical results shown for these examples may differ between
   platforms as the results depend on the SPICE kernels used as input
   and the machine specific arithmetic implementation.

   1) Determine the times of local maxima of the angular separation
      between the moon and sun as observed from earth from
      Jan 1, 2007 to Jan 1, 2008.

      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.


      function gfsep_ex1()

         MAXWIN  =  1000;
         TIMFMT  = 'YYYY-MON-DD HR:MN:SC.###### (TDB) ::TDB ::RND';

         %
         % Load kernels.
         %
         cspice_furnsh( 'gfsep_ex1.tm' );

         %
         % Store the time bounds of our search interval in
         % the cnfine confinement window.
         %
         et = cspice_str2et( { '2007 JAN 01', '2008 JAN 01'} );

         cnfine = cspice_wninsd( et(1), et(2) );

         %
         % Prompt for the inputs.
         %
         targ1  = input( 'First body     > ', 's' );
         targ2  = input( 'Second body    > ', 's' );
         obsrvr = input( 'Observing body > ', 's' );

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

         shape1 = 'SPHERE';
         frame1 = 'NULL';
         shape2 = 'SPHERE';
         frame2 = 'NULL';
         abcorr = 'NONE';
         relate = 'LOCMAX';
         nintvls = MAXWIN;

         result = cspice_gfsep( targ1,   shape1, frame1,                  ...
                                targ2,   shape2, frame2,                  ...
                                abcorr,  obsrvr, relate,                  ...
                                refval,  adjust, step,                    ...
                                nintvls, cnfine         );

         %
         % List the beginning and ending times in each interval
         % if result contains data.
         %
         for i=1:numel(result)/2

            [left, right] = cspice_wnfetd( result, i );

            output = cspice_timout( [left,right], TIMFMT );

            if( isequal( left, right) )

               disp( ['Event time: ' output(1,:)] )

            else

               disp( ['From : ' output(1,:)] )
               disp( ['To   : ' output(2,:)] )

            end

         end

         %
         % It's always good form to unload kernels after use,
         % particularly in Matlab due to data persistence.
         %
         cspice_kclear


      When this program was executed on a Mac/Intel/Octave6.x/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
      Event time: 2007-JAN-11 11:21:20.214305 (TDB)
      Event time: 2007-JAN-26 01:43:41.027309 (TDB)
      Event time: 2007-FEB-10 04:49:53.431964 (TDB)
      Event time: 2007-FEB-24 13:18:18.953256 (TDB)
      Event time: 2007-MAR-11 20:41:59.571964 (TDB)
      Event time: 2007-MAR-26 01:20:26.860201 (TDB)
      Event time: 2007-APR-10 10:24:39.017514 (TDB)
      Event time: 2007-APR-24 14:00:49.422728 (TDB)
      Event time: 2007-MAY-09 21:53:25.643532 (TDB)
      Event time: 2007-MAY-24 03:14:05.873982 (TDB)
      Event time: 2007-JUN-08 07:24:13.686616 (TDB)
      Event time: 2007-JUN-22 16:45:56.506850 (TDB)
      Event time: 2007-JUL-07 15:30:03.706532 (TDB)
      Event time: 2007-JUL-22 06:26:17.397353 (TDB)
      Event time: 2007-AUG-05 23:03:21.625229 (TDB)
      Event time: 2007-AUG-20 20:14:56.801678 (TDB)
      Event time: 2007-SEP-04 07:13:25.162360 (TDB)
      Event time: 2007-SEP-19 10:16:42.721117 (TDB)
      Event time: 2007-OCT-03 17:11:17.188939 (TDB)
      Event time: 2007-OCT-19 00:30:31.300060 (TDB)
      Event time: 2007-NOV-02 05:43:48.902220 (TDB)
      Event time: 2007-NOV-17 14:38:21.314771 (TDB)
      Event time: 2007-DEC-01 20:50:27.562519 (TDB)
      Event time: 2007-DEC-17 04:04:46.933247 (TDB)
      Event time: 2007-DEC-31 13:43:52.558812 (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/Octave6.x/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
      Event time: 2007-JAN-03 14:20:24.617627 (TDB)
      Event time: 2007-FEB-02 06:16:24.101517 (TDB)
      Event time: 2007-MAR-03 23:22:41.994972 (TDB)
      Event time: 2007-APR-02 16:49:16.135505 (TDB)
      Event time: 2007-MAY-02 09:41:43.830081 (TDB)
      Event time: 2007-JUN-01 01:03:44.527470 (TDB)
      Event time: 2007-JUN-30 14:15:26.576292 (TDB)
      Event time: 2007-JUL-30 01:14:49.000963 (TDB)
      Event time: 2007-AUG-28 10:39:01.388249 (TDB)
      Event time: 2007-SEP-26 19:25:51.509426 (TDB)
      Event time: 2007-OCT-26 04:30:56.625105 (TDB)
      Event time: 2007-NOV-24 14:31:04.331185 (TDB)
      Event time: 2007-DEC-24 01:40:12.235392 (TDB)


Particulars


   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 MiceGF.m).

   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 cspice_gfstol, e.g.

      cspice_gfstol( tolerance value );

   Call cspice_gfstol 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.

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 cspice_wncond.

   3)  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.

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

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

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

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

   8)  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.

   9)  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.

   10) 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.

   11) 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.

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

   13) If any of the input arguments, `targ1', `shape1', `frame1',
       `targ2', `shape2', `frame2', `abcorr', `obsrvr', `relate',
       `refval', `adjust', `step', `nintvls' or `cnfine', is
       undefined, an error is signaled by the Matlab error handling
       system.

   14) If any of the input arguments, `targ1', `shape1', `frame1',
       `targ2', `shape2', `frame2', `abcorr', `obsrvr', `relate',
       `refval', `adjust', `step', `nintvls' or `cnfine', is not of
       the expected type, or it does not have the expected dimensions
       and size, an error is signaled by the Mice interface.

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
      cspice_furnsh.

   -  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 cspice_furnsh.

   -  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.

Restrictions


   1)  The kernel files to be used by this routine must be loaded
       (normally using the Mice routine cspice_furnsh) 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 SPICE, a direct
       search for zero angular separation of two point targets will
       always fails, i.e.,

          relate = '='
          refval = 0.0

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

Required_Reading


   MICE.REQ
   GF.REQ
   SPK.REQ
   CK.REQ
   TIME.REQ
   WINDOWS.REQ

Literature_References


   None.

Author_and_Institution


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

Version


   -Mice Version 1.1.0, 03-NOV-2021 (EDW) (JDR)

       Updated header to describe use of expanded confinement window.

       Edited the header to comply with NAIF standard. Added
       example's meta-kernel, modified example code to prompt for
       the required inputs and added a second example.

       Added -Parameters, -Exceptions, -Files, -Restrictions,
       -Literature_References and -Author_and_Institution sections.

       Eliminated use of "lasterror" in rethrow.

       Removed reference to the function's corresponding CSPICE header from
       -Required_Reading section.

   -Mice Version 1.0.3, 17-MAR-2015 (EDW)

       Edited -I/O section to conform to NAIF standard for Mice
       documentation.

       Typo correction in version IDs in -Version section.

   -Mice Version 1.0.2, 05-SEP-2012 (EDW)

       Edit to comments to correct search description.

       Header updated to describe use of cspice_gfstol.

   -Mice Version 1.0.1, 29-DEC-2009 (EDW)

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

   -Mice Version 1.0.0, 15-APR-2009 (NJB) (EDW)

Index_Entries


   GF angular separation search


Fri Dec 31 18:44:25 2021