Procedure

     CKE02 ( C-kernel, evaluate pointing record, data type 2 )

     SUBROUTINE CKE02 ( NEEDAV, RECORD, CMAT, AV, CLKOUT )

Abstract

     Evaluate a pointing record returned by CKR02 from a CK data type 2
     segment. Return the C-matrix and angular velocity vector
     associated with the time CLKOUT.

Required_Reading

     CK
     ROTATION

Keywords

     POINTING

Declarations

     IMPLICIT NONE

     LOGICAL               NEEDAV
     DOUBLE PRECISION      RECORD ( *    )
     DOUBLE PRECISION      CMAT   ( 3, 3 )
     DOUBLE PRECISION      AV     ( 3    )
     DOUBLE PRECISION      CLKOUT

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     NEEDAV     I   .TRUE. if angular velocity is requested.
     RECORD     I   Data type 2 pointing record.
     CMAT       O   C-matrix.
     AV         O   Angular velocity vector.
     CLKOUT     O   SCLK associated with C-matrix.

Detailed_Input

     NEEDAV   is .TRUE. if angular velocity is requested.

     RECORD   is a set of double precision numbers returned by CKR02
              that contain sufficient information from a data type
              2 pointing segment to evaluate the C-matrix and the
              angular velocity vector for a particular instance.

              The contents of RECORD are as follows:

                 RECORD( 1  ) = start SCLKDP of interval

                 RECORD( 2  ) = SCLK for which pointing was found

                 RECORD( 3  ) = seconds / tick rate

                 RECORD( 4  ) = q0
                 RECORD( 5  ) = q1
                 RECORD( 6  ) = q2
                 RECORD( 7  ) = q3

                 RECORD( 8  ) = av1
                 RECORD( 9  ) = av2
                 RECORD( 10 ) = av3

              The quantities q0 - q3 are the components of the
              quaternion that represents the C - matrix associated
              with the start of the interval. The quantities av1,
              av2, and av3 are the components of the angular velocity
              vector.

Detailed_Output

     CMAT     is a rotation matrix that transforms the components
              of a vector expressed in the inertial frame given in
              the segment to components expressed in the instrument
              fixed frame at the returned time.

              Thus, if a vector v has components x, y, z in the
              inertial frame, then v has components x', y', z' in the
              instrument fixed frame where:

                   [ x' ]     [          ] [ x ]
                   | y' |  =  |   CMAT   | | y |
                   [ z' ]     [          ] [ z ]

              If the x', y', z' components are known, use the
              transpose of the C-matrix to determine x, y, z as
              follows.

                   [ x ]      [          ]T    [ x' ]
                   | y |  =   |   CMAT   |     | y' |
                   [ z ]      [          ]     [ z' ]
                            (Transpose of CMAT)

     AV       is the angular velocity vector. The angular velocity
              contained in RECORD is returned only if NEEDAV is .TRUE.

              The direction of the angular velocity vector gives
              the right-handed axis about which the instrument fixed
              reference frame is rotating. The magnitude of AV is
              the magnitude of the instantaneous velocity of the
              rotation, in radians per second.

              The angular velocity vector is returned in component
              form

                       AV = [ AV1  , AV2  , AV3  ]

              which is in terms of the inertial coordinate frame
              specified in the segment descriptor.

     CLKOUT   is the encoded SCLK associated with the returned
              C-matrix and angular velocity vector.

Parameters

     None.

Exceptions

     1)  No checking is done to determine whether RECORD is valid.

Files

     None.

Particulars

     For a detailed description of the structure of a type 2 pointing
     segment, see the CK Required Reading.

     Pointing data in a type 2 segment consists of intervals during
     which the orientation of the spacecraft structure can be described
     by an initial C-matrix and a constant angular velocity vector.
     From the information contained in the pointing record returned by
     CKR02, this subroutine calculates and returns the C-matrix
     associated with the time returned by CKR02. It also returns the
     angular velocity vector contained in the pointing record.

Examples

     A call to a CKEnn routine is almost always preceded by a call to
     the corresponding CKRnn routine, which gets the logical record
     that CKEnn evaluates.

     The following code fragment searches through a file (represented
     by HANDLE) for all segments applicable to the Voyager 2 wide angle
     camera, for a particular spacecraft clock time, that are of data
     types 1 or 2. It then evaluates the pointing for that epoch and
     prints the result.


           SC     = -32
           INST   = -32002
     C
     C     Load the Voyager 2 spacecraft clock kernel and the C-kernel.
     C
           CALL FURNSH ( 'VGR_SCLK.TSC'        )
           CALL DAFOPR ( 'VGR2_CK.BC',  HANDLE )

     C
     C     Get the spacecraft clock time. Must encode it for use
     C     in the C-kernel.
     C

           WRITE (*,*) 'Enter spacecraft clock time string:'
           READ (*,FMT='(A)') SCLKCH
           CALL SCENCD ( SC, SCLKCH, SCLKDP )

     C
     C     Search from the beginning through all segments.
     C
           CALL DAFBFS ( HANDLE )
           CALL DAFFNA ( SFND   )

           DO WHILE ( SFND )

              CALL DAFGN ( IDENT                 )
              CALL DAFGS ( DESCR                 )
              CALL DAFUS ( DESCR, 2, 6, DCD, ICD )

              IF ( INST          .EQ. ICD( 1 )  .AND.
          .        SCLKDP + TOL  .GE. DCD( 1 )  .AND.
          .        SCLKDP - TOL  .LE. DCD( 2 ) ) THEN

                 DTYPE = ICD ( 3 )

                 IF ( DTYPE .EQ. 1 ) THEN

                    CALL CKR01 ( HANDLE, DESCR, SCLKDP, TOL, NEEDAV,
          .                      RECORD, FOUND                       )

                    IF ( FOUND ) THEN
                       CALL CKE01 ( NEEDAV, RECORD, CMAT, AV, CLKOUT )
                    END IF

                 ELSE  IF ( DTYPE .EQ. 2 ) THEN

                    CALL CKR02 ( HANDLE, DESCR, SCLKDP, TOL,
          .                      RECORD, FOUND )

                    IF ( FOUND ) THEN
                       CALL CKE02 ( NEEDAV, RECORD, CMAT, AV, CLKOUT )
                    END IF

                 END IF

                 IF ( FOUND ) THEN

                    WRITE (*,*) 'Segment descriptor and identifier:'
                    WRITE (*,*) DCD, ICD
                    WRITE (*,*) IDENT

                    WRITE (*,*) 'C-matrix:'
                    WRITE (*,*) CMAT

                 END IF

              END IF

              CALL DAFFNA ( SFND )

           END DO

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     J. Diaz del Rio    (ODC Space)
     J.M. Lynch         (JPL)
     B.V. Semenov       (JPL)
     W.L. Taber         (JPL)
     E.D. Wright        (JPL)

Version

    SPICELIB Version 1.1.0, 12-AUG-2021 (JDR)

        Added IMPLICIT NONE statement.

        Edited the header to comply with NAIF standard.

    SPICELIB Version 1.0.3, 31-JAN-2008 (BVS)

        Removed non-standard end-of-declarations marker
        'C%&END_DECLARATIONS' from comments.

    SPICELIB Version 1.0.2, 22-AUG-2006 (EDW)

        Replaced references to LDPOOL with references
        to FURNSH.

    SPICELIB Version 1.0.1, 10-MAR-1992 (WLT)

        Comment section for permuted index source lines was added
        following the header.

    SPICELIB Version 1.0.0, 30-AUG-1991 (JML)