| ckfrot_c |
|
Table of contents
Procedure
ckfrot_c ( CK frame, find position rotation )
void ckfrot_c ( SpiceInt inst,
SpiceDouble et,
SpiceDouble rotate [3][3],
SpiceInt * ref,
SpiceBoolean * found )
AbstractFind the position rotation matrix from a C-kernel (CK) frame with the specified frame class ID (CK ID) to the base frame of the highest priority CK segment containing orientation data for this CK frame at the time requested. Required_ReadingCK KeywordsPOINTING Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- inst I Frame class ID (CK ID) of a CK frame. et I Epoch measured in seconds past J2000 TDB. rotate O Rotation matrix from CK frame to frame `ref'. ref O Frame ID of the base reference. found O SPICETRUE when requested pointing is available. Detailed_Input
inst is the unique frame class ID (CK ID) of the CK frame for
which data is being requested.
et is the epoch for which the position rotation is desired.
`et' should be given in seconds past the epoch of J2000
TDB.
Detailed_Output
rotate is a position rotation matrix that converts positions
relative to the CK frame given by its frame class ID,
`inst', to positions relative to the base frame given by
its frame ID, `ref'.
Thus, if a position S has components x,y,z in the CK
frame, then S has components x', y', z' in the base
frame.
.- -. .- -. .- -.
| x' | | | | x |
| y' | = | rotate | | y |
| z' | | | | z |
`- -' `- -' `- -'
ref is the ID code of the base reference frame to which
`rotate' will transform positions.
found is SPICETRUE if a record was found to satisfy the pointing
request. `found' will be SPICEFALSE otherwise.
ParametersNone. Exceptions
1) If no CK files were loaded prior to calling this routine, an
error is signaled by a routine in the call tree of this
routine.
2) If no SCLK correlation data needed to read CK files were
loaded prior to calling this routine, an error is signaled by
a routine in the call tree of this routine.
3) If the input time `et' cannot be converted to an encoded SCLK
time, using SCLK data associated with `inst', an error is
signaled by a routine in the call tree of this routine.
Filesckfrot_c searches through loaded CK files to locate a segment that can satisfy the request for position rotation data for the CK frame with the specified frame class ID at time `et'. You must load a CK file containing such data before calling this routine. You must also load SCLK and possibly LSK files needed to convert the input `et' time to the encoded SCLK time with which the orientation data stored inside that CK is tagged. Particularsckfrot_c searches through loaded CK files to satisfy a pointing request. Last-loaded files are searched first, and individual files are searched in backwards order, giving priority to segments that were added to a file later than the others. The search ends when a segment is found that can give pointing for the specified CK frame at the request time. Segments with and without angular velocities are considered by this routine. This routine uses the ckmeta_c routine to determine the SCLK ID used to convert the input `et' time to the encoded SCLK time used to look up pointing data in loaded CK files. Examples
The numerical results shown for this example may differ across
platforms. The results depend on the SPICE kernels used as
input, the compiler and supporting libraries, and the machine
specific arithmetic implementation.
1) Use ckfrot_c to compute the instantaneous angular velocity
vector for the Mars Global Surveyor (MGS) spacecraft frame,
"MGS_SPACECRAFT", relative to the inertial frame used as the
base frame in CK files containing MGS spacecraft orientation
at 2003-JUL-25 13:00:00. The frame class ID (CK ID) for the
"MGS_SPACECRAFT" frame is -94000.
Suppose that r(t) is the rotation matrix whose columns
represent the inertial pointing vectors of the MGS spacecraft
axes at time `t'.
Then the angular velocity vector points along the vector given
by:
T
limit axis( r(t+h)r )
h-->0
And the magnitude of the angular velocity at time `t' is given
by:
T
d angle ( r(t+h)r(t) )
------------------------ at h = 0
dh
Use the meta-kernel shown below to load the required SPICE
kernels.
KPL/MK
File name: ckfrot_ex1.tm
This meta-kernel is intended to support operation of SPICE
example programs. The kernels shown here should not be
assumed to contain adequate or correct versions of data
required by SPICE-based user applications.
In order for an application to use this meta-kernel, the
kernels referenced here must be present in the user's
current working directory.
The names and contents of the kernels referenced
by this meta-kernel are as follows:
File name Contents
--------- --------
naif0012.tls Leapseconds
mgs_sclkscet_00061.tsc MGS SCLK coefficients
mgs_sc_ext12.bc MGS s/c bus attitude
\begindata
KERNELS_TO_LOAD = ( 'naif0012.tls',
'mgs_sclkscet_00061.tsc',
'mgs_sc_ext12.bc' )
\begintext
End of meta-kernel
Example code begins here.
/.
Program ckfrot_ex1
./
#include <stdio.h>
#include "SpiceUsr.h"
int main( )
{
/.
Local parameters.
./
#define EPOCH "2003-JUL-25 13:00:00"
#define INST -94000
/.
Local variables.
./
SpiceDouble angle;
SpiceDouble angvel [3];
SpiceDouble axis [3];
SpiceDouble et;
SpiceDouble infrot [3][3];
SpiceDouble h;
SpiceDouble ret [3][3];
SpiceDouble reth [3][3];
SpiceInt ref;
SpiceInt refh;
SpiceBoolean found;
SpiceBoolean foundh;
/.
Load the required LSK, SCLK and CK. Use a
meta-kernel for convenience.
./
furnsh_c ( "ckfrot_ex1.tm" );
/.
First convert the time to seconds past J2000. Set the
delta time (1 ms).
./
str2et_c ( EPOCH, &et );
h = 1.e-3;
/.
Now, look up the rotation from the MGS spacecraft
frame specified by its frame class ID (CK ID) to a
base reference frame (returned by ckfrot_c), at `et'
and et+h.
./
ckfrot_c ( INST, et, ret, &ref, &found );
ckfrot_c ( INST, et+h, reth, &refh, &foundh );
/.
If both rotations were computed and if the base
reference frames are the same, compute the
instantaneous angular velocity vector.
./
if ( found && foundh && ref == refh )
{
/.
Compute the infinitesimal rotation r(t+h)r(t)^T.
./
mxmt_c ( reth, ret, infrot );
/.
Compute the `axis' and `angle' of the infinitesimal
rotation.
./
raxisa_c ( infrot, axis, &angle );
/.
Scale `axis' to get the angular velocity vector.
./
vscl_c ( angle/h, axis, angvel );
/.
Output the results.
./
printf( "Instantaneous angular velocity vector:\n" );
printf( "%15.10f %14.10f %14.10f\n",
angvel[0], angvel[1], angvel[2] );
printf( "Reference frame ID: %4d\n", (int)ref );
}
else
{
printf( "ERROR: data not found or frame mismatch.\n" );
}
return ( 0 );
}
When this program was executed on a Mac/Intel/cc/64-bit
platform, the output was:
Instantaneous angular velocity vector:
0.0001244121 0.0008314866 0.0003028634
Reference frame ID: 1
Restrictions
1) A CK file must be loaded prior to calling this routine.
2) LSK and SCLK files needed for time conversions must be loaded
prior to calling this routine.
Literature_ReferencesNone. Author_and_InstitutionJ. Diaz del Rio (ODC Space) Version-CSPICE Version 1.0.0, 13-DEC-2021 (JDR) Index_Entriesget instrument frame rotation and reference frame |
Fri Dec 31 18:41:02 2021