Procedure

     SPKPVN ( S/P Kernel, position and velocity in native frame )

     SUBROUTINE SPKPVN ( HANDLE, DESCR, ET, REF, STATE, CENTER )

Abstract

     Return, for a specified SPK segment and time, the state (position
     and velocity) of the segment's target body relative to its center
     of motion.

Required_Reading

     SPK

Keywords

     EPHEMERIS

Declarations

     IMPLICIT NONE

     INCLUDE 'spkrec.inc'

     INTEGER               HANDLE
     DOUBLE PRECISION      DESCR    ( 5 )
     DOUBLE PRECISION      ET
     INTEGER               REF
     DOUBLE PRECISION      STATE    ( 6 )
     INTEGER               CENTER

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     HANDLE     I   File handle.
     DESCR      I   Segment descriptor.
     ET         I   Target epoch.
     REF        O   Target reference frame.
     STATE      O   Position, velocity.
     CENTER     O   Center of state.
     MAXREC     P   Maximum length of records returned by SPKRnn.

Detailed_Input

     HANDLE,
     DESCR    are the file handle assigned to a SPK file, and the
              descriptor for a segment within the file. Together
              they determine the ephemeris data from which the
              state of the body is to be computed.

     ET       is the epoch (ephemeris time) at which the state
              is to be computed.

Detailed_Output

     REF      is the id-code of the reference frame to
              which the vectors returned by the routine belong.

     STATE    is a 6-dimensional vector that contains the position and
              velocity, at epoch ET, for whatever body is covered by
              the specified segment. STATE has six elements: the first
              three contain the body's position; the last three contain
              the body's velocity. These vectors are rotated into the
              specified  reference frame, the origin of which is
              located at the center of motion for the body (see CENTER,
              below). Units are always km and km/sec.

     CENTER   is the integer ID code of the center of motion for
              the state.

Parameters

     MAXREC   is the maximum length of a record returned by any of
              data type-specific routines SPKRnn, which are called
              by SPKPVN (see $Particulars).

Exceptions

     1)  If the segment type is not supported by the current
         version of SPKPVN, the error SPICE(SPKTYPENOTSUPP)
         is signaled.

Files

     See argument HANDLE.

Particulars

     SPKPVN is the most basic of the SPK readers, the reader upon
     which SPKPV and SPKGEO, etc. are built. It should not normally
     be called directly except in cases where some optimization is
     required. (That is, where the calling program has prior knowledge
     of the center-barycenter shifts to be performed, or a non-standard
     method of determining the files and segments to be used when
     computing states.)

     This is the only reader which makes distinctions between the
     various segment types in the SPK format. The complete list
     of types currently supported is shown below.

        Type   Description
        ----   -----------------------
           1   Difference Lines
           2   Chebyshev (P)
           3   Chebyshev (P,V)
           5   Two body propagation between discrete states
           8   Lagrange interpolation, equally spaced discrete states
           9   Lagrange interpolation, unequally spaced discrete states
          12   Hermite interpolation, equally spaced discrete states
          13   Hermite interpolation, unequally spaced discrete states
          14   Chebyshev Unequally spaced
          15   Precessing Ellipse
          17   Equinoctial Elements
          18   ESOC/DDID Hermite/Lagrange Interpolation
          19   ESOC/DDID Piecewise Interpolation
          20   Chebyshev (V)
          21   Extended Modified Difference Array

     SPKPVN is the only reader that needs to be changed in order to
     add a new segment type to the SPK format. If a new data type is
     added, the following steps should be taken:

     1) Write two new routines, SPKRnn and SPKEnn, to read and
        evaluate, respectively, a record from a data type nn segment.

     2) Insert a new case into the body of SPKPVN to accommodate the
        new type.

     3) If necessary, adjust the parameter MAXREC, above, so that it
        is large enough to encompass the maximum size of a record
        returned by SPKRnn and passed to SPKEnn.

        The maximum record lengths for each data type currently
        supported are as follows:

                  Data type       Maximum record length
                  ---------       ---------------------
                      1                    71
                      2                    87
                      3                   171
                      5                    15
                      8                   171
                      9                   197
                     12                    87
                     13                    99
                     14                 Variable
                     15                    16
                     17                    12
                     18                   198
                     19                   198
                     20                   159
                     21                   112

Examples

     In the following code fragment, an entire SPK file is searched
     for segments containing a particular epoch. For each one found,
     the body, center, segment identifier, and range at the epoch
     are printed out.

        CALL DAFOPR ( 'TEST.SPK', HANDLE )
        CALL DAFBFS (             HANDLE )

        CALL DAFFNA ( FOUND  )

        DO WHILE ( FOUND )

           CALL DAFGS ( DESCR )
           CALL DAFUS ( DESCR, 2, 6, DC, IC )

           IF ( DC(1) .LE. ET  .AND.  ET .LE. DC(2) ) THEN
              CALL SPKPVN ( HANDLE, DESCR, ET, REF, STATE, CENTER )
              CALL DAFGN  ( IDENT )
              CALL FRMNAM ( REF, FRAME )
              WRITE (*,*)
              WRITE (*,*) 'Body   = ', IC(1)
              WRITE (*,*) 'Center = ', CENTER,
              WRITE (*,*) 'ID     = ', IDENT
              WRITE (*,*) 'Frame  = ', FRAME
              WRITE (*,*) 'Range  = ', VNORM ( STATE )
           END IF

           CALL DAFFNA ( FOUND )

        END DO

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

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

Version

    SPICELIB Version 4.0.1, 27-AUG-2021 (JDR)

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

    SPICELIB Version 4.0.0, 23-DEC-2013 (NJB)

        Added support for types 19, 20 and 21. Added header
        comments giving description for types 18, 19,
        and 21. Removed header reference to type 4.

    SPICELIB Version 3.0.0, 16-AUG-2002 (NJB)

        Added support for type 18. This routine now uses the
        include file spkrec.inc to declare the record size.

        Corrected header comments giving record sizes for types
        8, 9, 12, 13.

    SPICELIB Version 2.0.0, 06-NOV-1999 (NJB)

        Added support for types 12 and 13.

    SPICELIB Version 1.1.0, 07-JAN-1997 (WLT)

        Added support for type 17.

    SPICELIB Version 1.0.0, 19-SEP-1995 (WLT)