Procedure

     SPKE18 ( S/P Kernel, evaluate, type 18 )

     SUBROUTINE SPKE18 ( ET, RECORD, STATE )

Abstract

     Evaluate a single data record from a type 18 SPK segment.

Required_Reading

     SPK

Keywords

     EPHEMERIS

Declarations

     IMPLICIT NONE

     INCLUDE 'spk18.inc'
     INCLUDE 'spkrec.inc'

     DOUBLE PRECISION      ET
     DOUBLE PRECISION      RECORD   ( * )
     DOUBLE PRECISION      STATE    ( 6 )

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     MAXREC     P   Maximum size of SPK record.
     ET         I   Epoch for which a state is desired.
     RECORD     I   Record from a type 18 SPK segment valid for ET.
     STATE      O   State (position and velocity) at epoch ET.

Detailed_Input

     ET       is the epoch for which a state vector is desired.

     RECORD   is a record from a type 18 SPK 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:

                 +----------------------+
                 | subtype code         |
                 +----------------------+
                 | number of packets (n)|
                 +----------------------+
                 | packet 1             |
                 +----------------------+
                 | packet 2             |
                 +----------------------+
                          .
                          .
                          .
                 +----------------------+
                 | packet n             |
                 +----------------------+
                 | epochs 1--n          |
                 +----------------------+

Detailed_Output

     STATE    is the state vector at epoch ET. Its contents are, in
              order, X, Y, Z, X', Y', and Z'. Units are km and km/sec.

Parameters

     MAXREC   is the maximum size of SPK record. See the SPICELIB
              routine SPKPVN for details.

Exceptions

     1)  This routine assumes that the input record is valid.

Files

     None.

Particulars

     The exact format and structure of type 18 (MEX/Rosetta Orbit
     file interpolation) SPK segments is described in the SPK
     Required Reading.

Examples

     The SPKEnn routines are almost always used in conjunction with
     the corresponding SPKRnn routines, which read the records from
     SPK files.

     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 before evaluating the record to obtain a
     state vector, 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. 18 ) THEN

              CALL SPKR18 ( HANDLE, DESCR, ET, RECORD )
                  .
                  .  Look at the RECORD data.
                  .
              CALL SPKE18 ( ET, RECORD, STATE )
                  .
                  .  Check out the evaluated state.
                  .
           END IF

Restrictions

     1)  This routine assumes that the input record is valid. Any
         checking of the input data is assumed to have been performed
         when the source SPK file was created.

Literature_References

     None.

Author_and_Institution

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

Version

    SPICELIB Version 1.1.1, 16-AUG-2021 (JDR)

        Edited the header to comply with NAIF standard. Removed
        unnecessary $Revisions section.

    SPICELIB Version 1.1.0, 05-NOV-2005 (NJB)

        Updated to remove non-standard use of duplicate arguments
        in XPOSEG and LGRINT calls.

    SPICELIB Version 1.0.0, 17-AUG-2002 (NJB)