| cke04 |
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Table of contents
Procedure
CKE04 ( C-kernel, evaluate pointing record, type 4 )
SUBROUTINE CKE04 ( NEEDAV, RECORD, CMAT, AV, CLKOUT )
Abstract
Evaluate a pointing record returned by CKR04 from a CK type 4
segment. Return the C-matrix and angular velocity vector
associated with the time CLKOUT.
Required_Reading
CK
Keywords
POINTING
Declarations
IMPLICIT NONE
INCLUDE 'ckparam.inc'
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 4 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
CKR04. RECORD must have the following structure:
---------------------------------------------------
| Encoded onboard time which is the closest |
| to SCLKDP and belongs to one of approximation |
| intervals |
---------------------------------------------------
| encoded SCLK time of the midpoint of |
| interpolation interval |
---------------------------------------------------
| radii of interpolation interval |
| expressed as double precision SCLK ticks |
---------------------------------------------------
| Number of coefficients for q0 |
---------------------------------------------------
| Number of coefficients for q1 |
---------------------------------------------------
| Number of coefficients for q2 |
---------------------------------------------------
| Number of coefficients for q3 |
---------------------------------------------------
| Number of coefficients for AV1 |
---------------------------------------------------
| Number of coefficients for AV2 |
---------------------------------------------------
| Number of coefficients for AV3 |
---------------------------------------------------
| q0 Cheby coefficients |
---------------------------------------------------
| q1 Cheby coefficients |
---------------------------------------------------
| q2 Cheby coefficients |
---------------------------------------------------
| q3 Cheby coefficients |
---------------------------------------------------
| AV1 Cheby coefficients (optional) |
---------------------------------------------------
| AV2 Cheby coefficients (optional) |
---------------------------------------------------
| AV3 Cheby coefficients (optional) |
---------------------------------------------------
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 of the instrument fixed
frame defined by CMAT. The angular velocity 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
See 'ckparam.inc'.
Exceptions
Error free.
1) No checking is done to determine whether RECORD is valid.
Files
None.
Particulars
For a detailed description of the structure of a type 4 pointing
segment, see the CK Required Reading file.
The work done by CKE04 is to calculate quaternion and angular
velocity components using Chebyshev polynomial approximation
parameters. The second step of evaluation is to convert the
pointing portion of the record from quaternion form to C-matrix
form.
The angular velocity vector will only be returned if it has been
requested. In other words, if NEEDAV is .TRUE., the routine will
expect the angular velocity component of the record to be
present.
Examples
The CKRnn routines are usually used in tandem with the CKEnn
routines, which evaluate the record returned by CKRnn to give
the pointing information and output time.
The following code fragment searches through all of the segments
in a file applicable to the Mars Global Surveyor spacecraft bus
that are of data type 4, for a particular spacecraft clock time.
It then evaluates the pointing for that epoch and prints the
result.
C
C CK parameters include file.
C
INCLUDE 'ckparam.inc'
C
C Local variables
C
CHARACTER*(20) SCLKCH
CHARACTER*(20) SCTIME
CHARACTER*(40) IDENT
DOUBLE PRECISION AV ( 3 )
DOUBLE PRECISION CLKOUT
DOUBLE PRECISION CMAT ( 3, 3 )
DOUBLE PRECISION DCD ( 2 )
DOUBLE PRECISION DESCR ( 5 )
DOUBLE PRECISION RECORD ( CK4RSZ )
DOUBLE PRECISION SCLKDP
DOUBLE PRECISION TOL
INTEGER HANDLE
INTEGER I
INTEGER ICD ( 6 )
INTEGER INST
INTEGER SC
LOGICAL FND
LOGICAL NEEDAV
LOGICAL SFND
C
C Initial values.
C
SC = -94
INST = -94000
NEEDAV = .FALSE.
C
C Load the MGS SCLK kernel and the C-kernel.
C
CALL FURNSH( 'MGS_SCLK.TSC' )
CALL DAFOPR( 'MGS_CK4.BC', HANDLE )
C
C Get the spacecraft clock time. Then encode it for use
C in the C-kernel.
C
CALL PROMPT( 'Enter SCLK string: ', SCLKCH )
CALL SCENCD( SC, SCLKCH, SCLKDP )
C
C Use a tolerance of 2 seconds (half of the nominal
C separation between MGS pointing instances ).
C
CALL SCTIKS ( SC, '0000000002:000', TOL )
C
C Search from the beginning of the CK file through all
C of the segments.
C
CALL DAFBFS( HANDLE )
CALL DAFFNA( SFND )
FND = .FALSE.
DO WHILE ( ( SFND ) .AND. ( .NOT. FND ) )
C
C Get the segment identifier and descriptor.
C
CALL DAFGN( IDENT )
CALL DAFGS( DESCR )
C
C Unpack the segment descriptor into its integer and
C double precision components.
C
CALL DAFUS( DESCR, 2, 6, DCD, ICD )
C
C Determine if this segment should be processed.
C
IF ( ( INST .EQ. ICD( 1 ) ) .AND.
. ( SCLKDP + TOL .GE. DCD( 1 ) ) .AND.
. ( SCLKDP - TOL .LE. DCD( 2 ) ) .AND.
. ( CK4DTP .EQ. ICD( 3 ) ) ) THEN
C
C Find CK 4 record covering requested time.
C
CALL CKR04( HANDLE, DESCR, SCLKDP, TOL, NEEDAV,
. RECORD, FND )
IF ( FND ) THEN
C
C Compute pointing using found CK 4 record.
C
CALL CKE04( NEEDAV, RECORD, CMAT, AV, CLKOUT)
CALL SCDECD( SC, CLKOUT, SCTIME )
WRITE (*,*)
WRITE (*,*) 'Segment identifier: ', IDENT
WRITE (*,*)
WRITE (*,*) 'Pointing returned for time: ',
. SCTIME
WRITE (*,*)
WRITE (*,*) 'C-matrix:'
WRITE (*,*)
WRITE (*,*) ( CMAT(1,I), I = 1, 3 )
WRITE (*,*) ( CMAT(2,I), I = 1, 3 )
WRITE (*,*) ( CMAT(3,I), I = 1, 3 )
WRITE (*,*)
END IF
END IF
CALL DAFFNA ( SFND )
END DO
Restrictions
1) No checking is done on the input RECORD.
Literature_References
None.
Author_and_Institution
J. Diaz del Rio (ODC Space)
B.V. Semenov (JPL)
E.D. Wright (JPL)
Y.K. Zaiko (JPL)
Version
SPICELIB Version 1.0.3, 12-AUG-2021 (JDR)
Edited the header to comply with NAIF standard.
SPICELIB Version 1.0.2, 18-APR-2014 (BVS)
Minor header edits.
SPICELIB Version 1.0.1, 22-AUG-2006 (EDW)
Replaced references to LDPOOL with references
to FURNSH.
SPICELIB Version 1.0.0, 05-MAY-1999 (YKZ) (BVS)
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Fri Dec 31 18:36:01 2021