Procedure

     SPKR21 ( Read SPK record from segment, type 21 )

     SUBROUTINE SPKR21 ( HANDLE, DESCR, ET, RECORD )

Abstract

     Read a single SPK data record from a segment of type 21
     (Extended Difference Lines).

Required_Reading

     SPK
     TIME

Keywords

     EPHEMERIS

Declarations

     IMPLICIT NONE

     INCLUDE 'spk21.inc'

     INTEGER               HANDLE
     DOUBLE PRECISION      DESCR    ( 5 )
     DOUBLE PRECISION      ET
     DOUBLE PRECISION      RECORD   ( * )

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     HANDLE     I   File handle.
     DESCR      I   Segment descriptor.
     ET         I   Evaluation epoch.
     RECORD     O   Data record.

Detailed_Input

     HANDLE,
     DESCR    are the file handle and segment descriptor for
              a SPK segment of type 21.

     ET       is an epoch for which a data record from a specific
              segment is required. The epoch is represented as
              seconds past J2000 TDB.

Detailed_Output

     RECORD   is a data record which, when evaluated at epoch ET,
              will give the state (position and velocity) of an
              ephemeris object, relative to its center of motion,
              in an inertial reference frame.

              The contents of RECORD are as follows:

                 RECORD(1):         The difference table size per
                                    Cartesian component. Call this
                                    size MAXDIM; then the difference
                                    line (MDA) size DLSIZE is

                                      ( 4 * MAXDIM ) + 11

                 RECORD(2)
                    ...
                 RECORD(1+DLSIZE):  An extended difference line.
                                    The contents are:

                    Dimension  Description
                    ---------  ----------------------------------
                    1          Reference epoch of difference line
                    MAXDIM     Stepsize function vector
                    1          Reference position vector,  x
                    1          Reference velocity vector,  x
                    1          Reference position vector,  y
                    1          Reference velocity vector,  y
                    1          Reference position vector,  z
                    1          Reference velocity vector,  z
                    MAXDIM,3   Modified divided difference
                               arrays (MDAs)
                    1          Maximum integration order plus 1
                    3          Integration order array

Parameters

     None.

Exceptions

     1)  If the maximum table size of the input record exceeds
         MAXTRM, the error SPICE(DIFFLINETOOLARGE) is signaled.

     2)  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

     See the SPK Required Reading file for a description of the
     structure of a data type 21 segment.

Examples

     The data returned by the SPKRnn routine is in its rawest form,
     taken directly from the segment. As such, it will be meaningless
     to a user unless he/she understands the structure of the data type
     completely. Given that understanding, however, the SPKRxx
     routines might be used to "dump" and check segment data for a
     particular epoch.


     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. 1 ) THEN
              CALL SPKR21 ( HANDLE, DESCR, ET, RECORD )
                  .
                  .  Look at the RECORD data.
                  .
           END IF

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     N.J. Bachman       (JPL)
     J. Diaz del Rio    (ODC Space)
     F.T. Krogh         (JPL)
     W.L. Taber         (JPL)
     I.M. Underwood     (JPL)

Version

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

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

    SPICELIB Version 1.0.0, 16-JAN-2014 (NJB) (FTK) (WLT) (IMU)