Procedure

     SPKR12 ( Read SPK record from segment, type 12 )

     SUBROUTINE SPKR12 ( HANDLE, DESCR, ET, RECORD )

Abstract

     Read a single data record from a type 12 SPK segment.

Required_Reading

     SPK

Keywords

     EPHEMERIS

Declarations

     IMPLICIT NONE

     INTEGER               MAXREC
     PARAMETER           ( MAXREC  = 129 )

     INTEGER               HANDLE
     DOUBLE PRECISION      DESCR    ( * )
     DOUBLE PRECISION      ET
     DOUBLE PRECISION      RECORD   ( * )

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     HANDLE     I   Handle of the open SPK file.
     DESCR      I   Descriptor of the segment with the desired record.
     ET         I   Epoch used to identify the desired record.
     RECORD     O   The desired type 12 SPK record.

Detailed_Input

     HANDLE   is the handle of the open SPK file which contains
              the segment of interest.

     DESCR    is the descriptor for a type 12 SPK segment that
              contains the record of interest.

     ET       is the target epoch used to determine the
              particular record to be obtained from the SPK
              segment.

Detailed_Output

     RECORD   is the record from the specified segment which,
              when evaluated at epoch ET, will give the state
              (position and velocity) of some body, relative
              to some center, in some inertial reference frame.

              The structure of the record is as follows:

                 +----------------------+
                 | number of states (n) |
                 +----------------------+
                 | start epoch          |
                 +----------------------+
                 | step size            |
                 +----------------------+
                 | state 1 (6 elts.)    |
                 +----------------------+
                 | state 2 (6 elts.)    |
                 +----------------------+
                             .
                             .
                             .
                 +----------------------+
                 | state n (6 elts.)    |
                 +----------------------+

Parameters

     None.

Exceptions

     1)  If an error occurs while looking up SPK data, the error is
         signaled by a routine in the call tree of this routine.

Files

     See argument HANDLE.

Particulars

     This subroutine will read a single record from a type 12 SPK
     segment. The record read will provide the data necessary to
     compute the state for the body designated by DESCR at epoch
     ET.

     The exact format and structure of a type 12 SPK segment is
     described in the SPK Required Reading.

Examples

     The data returned by the SPKRnn routine is in a raw form, taken
     directly from the segment. As such, it will be not be directly
     useful to a user unless they have a complete understanding of the
     structure of the data type. Given that understanding, however,
     the SPKRnn routines could be used to "dump" and check segment data
     for a particular epoch, as in the example which follows.


     C
     C     Get a segment applicable to a specified body and epoch.
     C
           CALL SPKSFS ( BODY, ET, HANDLE, DESCR, IDENT, FOUND )

     C
     C     Look at parts of the descriptor.
     C
           CALL DAFUS ( DESCR, 2, 6, DCD, ICD )
           CENTER = ICD( 2 )
           REF    = ICD( 3 )
           TYPE   = ICD( 4 )

           IF ( TYPE .EQ. 12 ) THEN
              CALL SPKR12 ( HANDLE, DESCR, ET, RECORD )
                  .
                  .  Look at the RECORD data.
                  .
           END IF

Restrictions

     1)  This subroutine should not be called directly by a casual
         user. It is intended for use by the subroutine SPKPVN, and
         certain tests for error conditions are not performed here, as
         SPKPVN will have already performed them.

Literature_References

     None.

Author_and_Institution

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

Version

    SPICELIB Version 1.0.1, 14-APR-2021 (JDR)

        Edited the header to comply with NAIF standard. Updated
        $Exceptions section. Moved SPK required reading from
        $Literature_References to $Required_Reading section.

    SPICELIB Version 1.0.0, 25-FEB-2000 (NJB)