Procedure

     SPKE20 ( SPK, evaluate Chebyshev polynomials, type 20 )

     SUBROUTINE SPKE20 ( ET, RECORD, XYZDOT )

Abstract

     Evaluate a single data record from an SPK or PCK segment of type
     20 (Chebyshev polynomials, velocity only).

Required_Reading

     SPK
     PCK

Keywords

     EPHEMERIS

Declarations

     IMPLICIT NONE

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

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     ET         I   Evaluation epoch.
     RECORD     I   Data record.
     XYZDOT     O   Three function components and their derivatives.

Detailed_Input

     ET       is the epoch at which a state vector or Euler angle
              state is to be computed. The epoch is represented as
              seconds past J2000 TDB.

     RECORD   is a data record which, when evaluated at epoch ET,
              will yield three function components and their
              derivatives with respect to time. The record
              structure for SPK type 20 data is:

                 +--------------------------------------+
                 | record size (excluding this element) |
                 +--------------------------------------+
                 | Coverage interval midpoint           |
                 +--------------------------------------+
                 | Coverage interval radius             |
                 +--------------------------------------+
                 | Coeffs for X velocity component      |
                 +--------------------------------------+
                 | Coeffs for Y velocity component      |
                 +--------------------------------------+
                 | Coeffs for Z velocity component      |
                 +--------------------------------------+
                 | X position component                 |
                 +--------------------------------------+
                 | Y position component                 |
                 +--------------------------------------+
                 | Z position component                 |
                 +--------------------------------------+

              In the above record

                 - Times are expressed as seconds past J2000 TDB.
                 - Position components have units of km.
                 - Velocity coefficients have units of km/s.

              See PCKE20 for a description of PCK type 20 records.

              PCK type 20 records contain coefficients for Euler
              angle rates and Euler angles corresponding to the
              interval midpoint. See PCKE20 for a more detailed
              description of the contents of PCK type 20 records.

Detailed_Output

     XYZDOT   is a 6-vector. In order, the components of XYZDOT are
              X, Y, Z, X', Y', and Z'. Units for state evaluations
              will be km and km/sec. Units for angles will be
              radians and radians/sec.

Parameters

     None.

Exceptions

     1)  If the input record contains an invalid coefficient count,
         the error SPICE(INVALIDCOUNT) is signaled.

     2)  If the input record contains invalid domain transformation
         parameters, an error is signaled by a routine in the
         call tree of this routine.

Files

     None.

Particulars

     This routine evaluates both type 20 SPK and PCK records.

     The exact format and structure of type 20 (Chebyshev polynomials,
     position only) segments are described in the SPK and PCK Required
     Reading files.

     A type 20 record contains three sets of Chebyshev coefficients---
     one set each for velocity components dX/dt, dY/dt, and dZ/dt. It
     also contains a position vector (or for a PCK record, Euler
     angles) associated with the midpoint of the record's coverage
     interval. The position (or orientation) is obtained from the
     indefinite integral of the velocity and the given vector.

Examples

     The data returned by the 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.

     The code fragment below demonstrates reading and evaluating
     a type 20 SPK record.


     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. 20 ) THEN

              CALL SPKR20 ( HANDLE, DESCR, ET, RECORD )
                  .
                  .  Look at the RECORD data.
                  .
              CALL SPKE20 ( ET, RECORD, XYZDOT )
                  .
                  .  Check out the evaluated state.
                  .
           END IF

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     N.J. Bachman       (JPL)
     J. Diaz del Rio    (ODC Space)
     R.E. Thurman       (JPL)
     K.S. Zukor         (JPL)

Version

    SPICELIB Version 1.1.0, 14-APR-2021 (JDR)

        Added IMPLICIT NONE statement.

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

    SPICELIB Version 1.0.0, 17-JAN-2014 (NJB) (RET) (KSZ)