Table of contents
CSPICE_CKFROT finds 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.
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 position rotation is desired.
[1,1] = size(et); double = class(et)
`et' should be given in seconds past the epoch of J2000
TDB.
the call:
[rotate, ref, found] = cspice_ckfrot( inst, et )
returns:
rotate 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'.
[3,3] = size(rotate); double = class(rotate)
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 the ID code of the base reference frame to which `rotate'
will transform positions.
[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_ckfrot 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.
function ckfrot_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( 'ckfrot_ex1.tm' );
%
% First convert the time to seconds past J2000. Set the
% delta time (1 ms).
%
[et] = cspice_str2et( EPOCH );
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 cspice_ckfrot), at `et'
% and et+h.
%
[ret, ref, found] = cspice_ckfrot( INST, et );
[reth, refh, foundh] = cspice_ckfrot( INST, et+h );
%
% 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.
%
infrot = reth * ret';
%
% Compute the `axis' and `angle' of the infinitesimal
% rotation.
%
[axis, angle] = cspice_raxisa( infrot );
%
% Scale `axis' to get the angular velocity vector.
%
angvel = angle/h * axis;
%
% Output the results.
%
fprintf( 'Instantaneous angular velocity vector:\n' )
fprintf( '%15.10f %14.10f %14.10f\n', angvel )
fprintf( 'Reference frame ID: %4d\n', ref )
else
fprintf( 'ERROR: data not found or frame mismatch.\n' )
end
%
% 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:
Instantaneous angular velocity vector:
0.0001244121 0.0008314866 0.0003028634
Reference frame ID: 1
cspice_ckfrot 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 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_ckfrot 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.
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 rotation and reference frame
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