Index Page gfrr_c
A B C D E F G H I J K L M N O P Q R S T U V W X
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
       void gfrr_c ( ConstSpiceChar     * target,
                     ConstSpiceChar     * abcorr,
                     ConstSpiceChar     * obsrvr,
                     ConstSpiceChar     * relate,
                     SpiceDouble          refval,
                     SpiceDouble          adjust,
                     SpiceDouble          step,
                     SpiceInt             nintvls,
                     SpiceCell          * cnfine,
                     SpiceCell          * result  )
#### Abstract
       Determine time intervals for which a specified constraint
       on the observer-target range rate is met.
#### Required_Reading
       GF
       NAIF_IDS
       SPK
       TIME
       WINDOWS
#### Keywords
       EVENT
       GEOMETRY
       EPHEMERIS
       SEARCH
       WINDOW
#### Brief_I/O
       Variable  I/O  Description
       --------  ---  --------------------------------------------------
       SPICE_GF_CNVTOL   P   Convergence tolerance
       target            I   Name of the target body.
       abcorr            I   Aberration correction flag.
       obsrvr            I   Name of the observing body.
       relate            I   Relational operator.
       refval            I   Reference value.
       adjust            I   Adjustment value for absolute extrema searches.
       step              I   Step size used for locating extrema and roots.
       nintvls           I   Workspace window interval count.
       cnfine           I-O  SPICE window to which the search is confined.
       result            O   SPICE window containing results.
#### Detailed_Input
       target      is the name of a target body. The target body is
                   an ephemeris object; its trajectory is given by
                   SPK data.

                   The string `target' is case-insensitive, and leading
                   and trailing blanks in `target' are not significant.
                   Optionally, you may supply a string containing the
                   integer ID code for the object. For example both
                   "MOON" and "301" are legitimate strings that indicate
                   the Moon is the target body.

                   The target and observer define a position vector which
                   points from the observer to the target; the time derivative
                   length of this vector is the "range rate" that serves as
                   the subject of the search performed by this routine.

       abcorr      indicates the aberration corrections to be applied to
                   the observer-target state vector to account for
                   one-way light time and stellar aberration.

                   Any aberration correction accepted by the SPICE
                   routine spkezr_c is accepted here. 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.

                   Case and blanks are not significant in the string
                   `abcorr'.

       obsrvr      is the name of the observing body. The observing body is
                   an ephemeris object; its trajectory is given by SPK
                   data. `obsrvr' is case-insensitive, and leading and
                   trailing blanks in `obsrvr' are not significant.
                   Optionally, you may supply a string containing the
                   integer ID code for the object. For example both "MOON"
                   and "301" are legitimate strings that indicate the Moon
                   is the observer.

       relate      is a relational operator used to define a constraint
                   on observer-target range rate. 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:

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

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

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

                     "ABSMAX"  Distance is at an absolute maximum.

                     "ABSMIN"  Distance is at an absolute  minimum.

                     "LOCMAX"  Distance is at a local maximum.

                     "LOCMIN"  Distance 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 distance of an absolute extremum.
                  The argument `adjust' (described below) is used to
                  specify this distance.

                  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.

                  Case is not significant in the string `relate'.

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

                  The units of `refval' are km/sec.

       adjust     is a parameter used to modify searches for absolute
                  extrema: when `relate' is set to "ABSMAX" or "ABSMIN" and
                  `adjust' is set to a positive value, gfdist_c will find
                  times when the observer-target range rate is within
                  `adjust' km/sec of the specified extreme value.

                  If `adjust' is non-zero and a search for an absolute
                  minimum `min' is performed, the result window contains
                  time intervals when the observer-target range rate has
                  values between `min' and min+adjust.

                  If the search is for an absolute maximum `max', the
                  corresponding range is from max-adjust to `max'.

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

       step       is the step size to be used in the search. `step' must
                  be short enough for a search using this step size
                  to locate the time intervals where the specified
                  range rate 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 a parameter specifying the number of intervals that
                  can be accommodated by each of the dynamically allocated
                  windows used internally by this routine. `nintvls' should
                  be at least as large as the number of intervals within
                  the search region on which the specified range rate
                  function is monotone increasing or decreasing. See
                  the Examples section below for code examples illustrating
                  the use of this parameter.

       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.

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

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

                  `result' must be declared with sufficient size to capture
                  the full set of time intervals within the search region
                  on which the specified constraint is satisfied.

                  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 be returned with a cardinality
                  of zero.
#### 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 is declared in the header file SpiceGF.h.
#### 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_c can be used to contract the result window.

       3)  If an error (typically cell overflow) occurs while performing
           window arithmetic, the error will be diagnosed by a routine
           in the call tree of this routine.

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

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

       6)  If 'adjust' is negative, the error SPICE(VALUEOUTOFRANGE) will
           signal from a routine in the call tree of this routine.

           A non-zero value for 'adjust' when 'relate' has any value other than
           "ABSMIN" or "ABSMAX" causes the error SPICE(INVALIDVALUE) to
           signal from a routine in the call tree of this routine.

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

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

       9)  If the workspace interval count is less than 1, the error
           SPICE(VALUEOUTOFRANGE) will be signaled.

       10) If the required amount of workspace memory cannot be
           allocated, the error SPICE(MALLOCFAILURE) will be
           signaled.

       11) If any input string argument pointer is null, the error
           SPICE(NULLPOINTER) will be signaled.

       12) If any input string argument is empty, the error
           SPICE(EMPTYSTRING) will be signaled.

       13) If either input cell has type other than SpiceDouble,
           the error SPICE(TYPEMISMATCH) is signaled.
#### Files
       Appropriate 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 for the
            time period defined by the confinement window 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_c.

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

       In all cases, kernel data are normally loaded once per program
       run, NOT every time this routine is called.
#### Particulars
       This routine determines if the caller-specified constraint condition
       on the geometric event (range rate) is satisfied for any time intervals
       within the confinement window 'cnfine'. If one or more such time
       intervals exist, those intervals are added to the 'result' window.

       This routine provides a simpler, but less flexible interface
       than does the routine gfevnt_c for conducting the searches for
       observer-target range rate value 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.

       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
       range rate 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 range rate 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 the set
       of points where an equality constraint is met, 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 via 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 range 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 range rate is zero can be
       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 range rate 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 shorter 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 either times when local extrema are
       attained or times when the range rate 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 convergence tolerance used by this
       routine is set via the parameter SPICE_GF_CNVTOL.

       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.

       To use a different tolerance value, a lower-level GF routine such
       as gfevnt_c  must be called. Making 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 affect 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.

       Consider the following example: suppose one wishes to find the
       times when the range rate between Io and the Earth attains a global
       minimum over some (lengthy) time interval. There is one local
       minimum every few days. The required step size for this search
       must be smaller than the shortest interval on which the range rate
       is monotone increasing or decreasing; this step size will be less
       than half the average time between local minima. However, we know
       that a global minimum can't occur when the Jupiter-Sun-Earth
       angle is greater than 90 degrees. We can use a step size of a
       half year to find the time period, within our original time
       interval, during which this angle is less than 90 degrees; this
       time period becomes the confinement window for our Earth-Io
       range rate search. This way we've used a quick (due to the large
       step size) search to cut out about half of the search period over
       which we must perform a slower search using a small step size.
#### 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.

       The examples shown below require a "standard" set of SPICE
       kernels. We list these kernels in a meta kernel named
       'standard.tm'.

       #include <stdio.h>
       #include <stdlib.h>
       #include <string.h>

       #include "SpiceUsr.h"

       #define       MAXWIN    20000
       #define       TIMFMT    "YYYY-MON-DD HR:MN:SC.###"
       #define       TIMLEN    41
       #define       NLOOPS    7

       int main( int argc, char **argv )
          {

          /.
          Create the needed windows. Note, one window
          consists of two values, so the total number
          of cell values to allocate is twice
          the number of intervals.
          ./
          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       * target = "MOON";
          SpiceChar       * abcorr = "NONE";
          SpiceChar       * obsrvr = "SUN";

          SpiceInt          count;
          SpiceInt          i;
          SpiceInt          j;

          ConstSpiceChar * relate [NLOOPS] = { "=",
                                               "<",
                                               ">",
                                               "LOCMIN",
                                               "ABSMIN",
                                               "LOCMAX",
                                               "ABSMAX",
                                             };

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

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

          wninsd_c ( begtim, endtim, &cnfine );

          /.
          Search using a step size of 1 day (in units of seconds).
          The reference value is .3365 km/s. We're not using the
          adjustment feature, so we set 'adjust' to zero.
          ./
          step   = spd_c();
          adjust = 0.;
          refval = .3365;

          for ( j = 0;  j < NLOOPS;  j++ )
             {

             printf ( "Relation condition: %s \n",  relate[j] );

             /.
             Perform the search. The SPICE window 'result' contains
             the set of times when the condition is met.
             ./
             gfrr_c ( target,
                      abcorr,
                      obsrvr,
                      relate[j],
                      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 ( "Start time, drdt = %s \n", begstr );
                   printf ( "Stop time,  drdt = %s \n", endstr );

                   }

                }

             printf("\n");

             }

          /.
          It's always good form to unload kernels after use,
          particularly in IDL due to data persistence.
          ./
          kclear_c();

          return( 0 );
          }

       The program outputs:

       Relation condition: =
       Start time, drdt = 2007-JAN-02 00:35:19.574
       Stop time,  drdt = 2007-JAN-02 00:35:19.574
       Start time, drdt = 2007-JAN-19 22:04:54.899
       Stop time,  drdt = 2007-JAN-19 22:04:54.899
       Start time, drdt = 2007-FEB-01 23:30:13.428
       Stop time,  drdt = 2007-FEB-01 23:30:13.428
       Start time, drdt = 2007-FEB-17 11:10:46.540
       Stop time,  drdt = 2007-FEB-17 11:10:46.540
       Start time, drdt = 2007-MAR-04 15:50:19.929
       Stop time,  drdt = 2007-MAR-04 15:50:19.929
       Start time, drdt = 2007-MAR-18 09:59:05.959
       Stop time,  drdt = 2007-MAR-18 09:59:05.959

       Relation condition: <
       Start time, drdt = 2007-JAN-02 00:35:19.574
       Stop time,  drdt = 2007-JAN-19 22:04:54.899
       Start time, drdt = 2007-FEB-01 23:30:13.428
       Stop time,  drdt = 2007-FEB-17 11:10:46.540
       Start time, drdt = 2007-MAR-04 15:50:19.929
       Stop time,  drdt = 2007-MAR-18 09:59:05.959

       Relation condition: >
       Start time, drdt = 2007-JAN-01 00:00:00.000
       Stop time,  drdt = 2007-JAN-02 00:35:19.574
       Start time, drdt = 2007-JAN-19 22:04:54.899
       Stop time,  drdt = 2007-FEB-01 23:30:13.428
       Start time, drdt = 2007-FEB-17 11:10:46.540
       Stop time,  drdt = 2007-MAR-04 15:50:19.929
       Start time, drdt = 2007-MAR-18 09:59:05.959
       Stop time,  drdt = 2007-APR-01 00:00:00.000

       Relation condition: LOCMIN
       Start time, drdt = 2007-JAN-11 07:03:58.988
       Stop time,  drdt = 2007-JAN-11 07:03:58.988
       Start time, drdt = 2007-FEB-10 06:26:15.439
       Stop time,  drdt = 2007-FEB-10 06:26:15.439
       Start time, drdt = 2007-MAR-12 03:28:36.404
       Stop time,  drdt = 2007-MAR-12 03:28:36.404

       Relation condition: ABSMIN
       Start time, drdt = 2007-JAN-11 07:03:58.988
       Stop time,  drdt = 2007-JAN-11 07:03:58.988

       Relation condition: LOCMAX
       Start time, drdt = 2007-JAN-26 02:27:33.766
       Stop time,  drdt = 2007-JAN-26 02:27:33.766
       Start time, drdt = 2007-FEB-24 09:35:07.816
       Stop time,  drdt = 2007-FEB-24 09:35:07.816
       Start time, drdt = 2007-MAR-25 17:26:56.150
       Stop time,  drdt = 2007-MAR-25 17:26:56.150

       Relation condition: ABSMAX
       Start time, drdt = 2007-MAR-25 17:26:56.150
       Stop time,  drdt = 2007-MAR-25 17:26:56.150
#### Restrictions
       1) The kernel files to be used by this routine must be loaded
          (normally using the CSPICE routine furnsh_c) before this
          routine is called.

       2) This routine has the side effect of re-initializing the
          range rate quantity utility package. Callers may themselves
          need to re-initialize the range rate quantity utility
          package after calling this routine.
#### Literature_References
       None.
#### Author_and_Institution
       N.J. Bachman   (JPL)
       E.D. Wright    (JPL)
#### Version
       -CSPICE Version 1.0.0, 26-AUG-2009 (EDW)
#### Index_Entries
     GF range rate search
#### Link to routine gfrr_c source file gfrr_c.c

    Wed Jun  9 13:05:24 2010