Table of contents
CSPICE_CKFXFM finds the state transformation 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 and angular velocity
data for this CK frame at the time requested.
Given:
inst the unique frame class ID (CK ID) of the CK frame for which
data is being requested.
[1,1] = size(inst); int32 = class(inst)
et the epoch for which the state transformation is desired.
[1,1] = size(et); double = class(et)
`et' should be given in seconds past the epoch of J2000
TDB.
the call:
[xform, ref, found] = cspice_ckfxfm( inst, et )
returns:
xform a state transformation matrix that converts states relative
to the CK frame given by its frame class ID, `inst', to
states relative to the base frame given by its frame ID,
`ref'.
[6,6] = size(xform); double = class(xform)
Thus, if a state S has components x, y, z, dx, dy, dz in
the CK frame, then S has components x', y', z', dx',
dy', dz' in the base frame `ref'.
.- -. .- -. .- -.
| x' | | | | x |
| y' | | | | y |
| z' | | | | z |
| dx' | = | xform | | dx |
| dy' | | | | dy |
| dz' | | | | dz |
`- -' `- -' `- -'
ref the ID code of the base reference frame to which `xform' will
transform states.
[1,1] = size(ref); int32 = class(ref)
found true if a record was found to satisfy the pointing request.
[1,1] = size(found); logical = class(found)
`found' will be false otherwise.
None.
Any numerical results shown for this example may differ between
platforms as the results depend on the SPICE kernels used as input
and the machine specific arithmetic implementation.
1) Use cspice_ckfxfm to compute the angular rate of rotation 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.
Use the meta-kernel shown below to load the required SPICE
kernels.
KPL/MK
File name: ckfxfm_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.
function ckfxfm_ex1()
%
% Local parameters.
%
EPOCH = '2003-JUL-25 13:00:00';
INST = -94000;
%
% Load the required LSK, SCLK and CK. Use a
% meta-kernel for convenience.
%
cspice_furnsh( 'ckfxfm_ex1.tm' );
%
% First convert the time to seconds past J2000.
%
[et] = cspice_str2et( EPOCH );
%
% Now, look up the state transformation from the MGS
% spacecraft frame specified by its frame class ID
% (CK ID) to a base reference frame (returned by
% cspice_ckfxfm), at `et'.
%
[xform, ref, found] = cspice_ckfxfm( INST, et );
%
% Next determine the angular velocity of the
% transformation.
%
[rot, av] = cspice_xf2rav( xform );
%
% The angular rate of change (in radians/second) is just
% the magnitude of `av'.
%
fprintf( 'Angular rate of change (rad/s): %19.16f\n', ...
cspice_vnorm( av ) )
%
% It's always good form to unload kernels after use,
% particularly in Matlab due to data persistence.
%
cspice_kclear
When this program was executed on a Mac/Intel/Octave6.x/64-bit
platform, the output was:
Angular rate of change (rad/s): 0.0008907319999591
cspice_ckfxfm 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.
Only segments with angular velocities are considered by this
routine.
This routine uses the cspice_ckmeta 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.
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.
4) If any of the input arguments, `inst' or `et', is undefined,
an error is signaled by the Matlab error handling system.
5) If any of the input arguments, `inst' or `et', is not of the
expected type, or it does not have the expected dimensions and
size, an error is signaled by the Mice interface.
cspice_ckfxfm searches through loaded CK files to locate a segment that
can satisfy the request for state transformation 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.
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.
CK.REQ
MICE.REQ
None.
J. Diaz del Rio (ODC Space)
-Mice Version 1.0.0, 13-DEC-2021 (JDR)
get instrument frame transformation and reference frame
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