CKE05 ( C-Kernel, evaluate, type 5 )
SUBROUTINE CKE05 ( NEEDAV, RECORD, CMAT, AV, CLKOUT )
Evaluate a single data record from a type 5 CK segment.
CK
POINTING
LOGICAL NEEDAV
DOUBLE PRECISION RECORD ( * )
DOUBLE PRECISION CMAT ( 3, 3 )
DOUBLE PRECISION AV ( 3 )
DOUBLE PRECISION CLKOUT
Variable I/O Description
-------- --- --------------------------------------------------
NEEDAV I True if angular velocity is requested.
RECORD I-O Data type 5 record.
CMAT O C-matrix.
AV O Angular velocity vector.
CLKOUT O SCLK associated with C-matrix.
NEEDAV is true if angular velocity is requested.
RECORD is a record from a type 5 CK segment which, when
evaluated at the epoch contained in its first
element, will give the attitude and angular velocity
of a spacecraft structure or instrument relative to a
base reference frame.
The structure of the record is as follows:
+----------------------+
| evaluation epoch |
+----------------------+
| subtype code |
+----------------------+
| number of packets (n)|
+----------------------+
| nominal SCLK rate |
+----------------------+
| packet 1 |
+----------------------+
| packet 2 |
+----------------------+
.
.
.
+----------------------+
| packet n |
+----------------------+
| epochs 1--n |
+----------------------+
See the CK Required Reading or the include file
ck05.inc for details on CK type 5 packet contents.
RECORD has been modified due to its use as a workspace array.
The contents are undefined.
CMAT is a rotation matrix that transforms the components
of a vector expressed in the base 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
base 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 base coordinate frame
specified in the segment descriptor.
CLKOUT is the encoded SCLK associated with the returned
C-matrix and angular velocity vector.
None.
1) If the input record contains an unrecognized subtype code,
the error SPICE(NOTSUPPORTED) is signaled.
None.
The exact format and structure of CK type 5 (MEX/Rosetta Attitude
file interpolation) CK segments is described in the CK Required
Reading.
The CKEnn routines are almost always used in conjunction with
the corresponding CKRnn routines, which read the records from
CK files.
The following code fragment searches through all of the segments
in a file applicable to the Mars Express spacecraft bus that
are of data type 5, for a particular spacecraft clock time.
It then evaluates the pointing for that epoch and prints the
result.
CHARACTER*(20) SCLKCH
CHARACTER*(20) SCTIME
CHARACTER*(40) IDENT
INTEGER I
INTEGER SC
INTEGER INST
INTEGER HANDLE
INTEGER DTYPE
INTEGER ICD ( 6 )
DOUBLE PRECISION SCLKDP
DOUBLE PRECISION TOL
DOUBLE PRECISION CLKOUT
DOUBLE PRECISION DESCR ( 5 )
DOUBLE PRECISION DCD ( 2 )
DOUBLE PRECISION RECORD ( 17 )
DOUBLE PRECISION CMAT ( 3, 3 )
DOUBLE PRECISION AV ( 3 )
LOGICAL NEEDAV
LOGICAL FND
LOGICAL SFND
SC = -41
INST = -41000
DTYPE = 5
NEEDAV = .FALSE.
C
C Load the MEX SCLK kernel and the C-kernel.
C
CALL FURNSH ( 'MEX_SCLK.TSC' )
CALL DAFOPR ( 'MEX_CK.BC', HANDLE )
C
C Get the spacecraft clock time. Then 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 Use a tolerance of 2 seconds ( half of the nominal
C separation between MEX 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.
. ( DTYPE .EQ. ICD( 3 ) ) ) THEN
CALL CKR05 ( HANDLE, DESCR, SCLKDP, TOL, NEEDAV,
. RECORD, FND )
IF ( FND ) THEN
CALL CKE05 (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
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 CK file was created.
2) This routine assumes that the input data are suitable for the
interpolation method indicated by the subtype code in the
input record. Since the mapping of rotations to quaternions
is multiple-valued, this routine assumes that whichever sign
minimizes the Euclidean distance between one quaternion and
the next is the correct sign. The same assumption is made
for quaternion derivatives.
None.
N.J. Bachman (JPL)
SPICELIB Version 2.0.0, 20-NOV-2006 (NJB)
Bug fix: this routine now assumes that angular velocity
and quaternion derivative values stored in the input
record have units of radians/second.
Bug fix: this routine no longer attempts to determine
the correct sign of quaternion derivatives. The caller
must supply quaternion derivatives that are suitable
for interpolation.
SPICELIB Version 1.3.0, 23-OCT-2005 (NJB)
Updated to remove non-standard use of duplicate arguments in
XPOSEG and VSCL calls. Replaced header reference to LDPOOL
with reference to FURNSH.
SPICELIB Version 1.2.0, 14-FEB-2003 (NJB)
Bug fix: angular velocity computation was modified to
match that used in the corresponding algorithm employed
by the MEX/Rosetta attitude file reader. The quaternion
derivative used to derive angular velocity now is the
derivative of the *unit* quaternion.
SPICELIB Version 1.1.0, 06-SEP-2002 (NJB)
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