Table of contents
CSPICE_RAV2XF determines the state transformation matrix
from a rotation matrix and the angular velocity of the
rotation.
Given:
rot a 3x3 double precision rotation matrix that gives the
transformation from some frame FRAME1 to another frame FRAME2.
help, rot
DOUBLE = Array[3,3]
av the double precision 3-vector angular velocity of the
transformation.
help, av
DOUBLE = Array[3]
In other words, if `p' is the position of a fixed point in
FRAME2, then from the point of view of FRAME1, `p' rotates (in a
right handed sense) about an axis parallel to `av'. Moreover the
rate of rotation in radians per unit time is given by the length
of `av'.
More formally, the velocity `v' of `p' in FRAME1 is
given by
T
v = av x ( rot * p )
the call:
cspice_rav2xf, rot, av, xform
returns:
xform a double precision, 6x6 state transformation matrix associated
with `rot' and `av'.
help, xform
DOUBLE = Array[6,6]
If `s1' is the state of an object with respect to FRAME1, then
the state `s2' of the object with respect to FRAME2 is given by
s2 = xform * s1
where "*" denotes Matrix-Vector multiplication.
None.
Any numerical results shown for these examples may differ between
platforms as the results depend on the SPICE kernels used as input
and the machine specific arithmetic implementation.
1) The following example program uses cspice_ckgpav to get C-matrix
and associated angular velocity vector for an image whose
SCLK count (un-encoded character string version) is known.
From that matrix and angular velocity vector, the associated
state transformation matrix is obtained.
Note that we need to load a SCLK kernel to convert from clock
string to "ticks." Although not required for older spacecraft
clocks, most modern spacecraft ones require a leapseconds
kernel to be loaded in addition to a SCLK kernel.
Use the meta-kernel shown below to load the required SPICE
kernels.
KPL/MK
File name: rav2xf_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
-------------------- -----------------------
cas00071.tsc CASSINI SCLK
04161_04164ra.bc CASSINI spacecraft
reconstructed CK
\begindata
KERNELS_TO_LOAD = ( 'cas00071.tsc'
'04161_04164ra.bc' )
\begintext
End of meta-kernel
Example code begins here.
PRO rav2xf_ex1
;;
;; Constants for this program.
;;
;; -- The code for the CASSINI spacecraft clock is -82.
;;
;; -- The code for CASSINI spacecraft reference frame is
;; -82000.
;;
;; -- Spacecraft clock tolerance is 1.0 seconds. This may
;; not be an acceptable tolerance for some applications.
;; It must be converted to "ticks" (units of encoded
;; SCLK) for input to cspice_ckgpav.
;;
;; -- The reference frame we want is J2000.
;;
META = 'rav2xf_ex1.tm'
REFFRM = 'J2000'
SCLKCH = '1/1465476046.160'
SCLTOL = '1.0'
SCID = -82L
INSTID = -82000L
;;
;; Load kernels.
;;
cspice_furnsh, META
;;
;; Convert tolerance from CASSINI formatted character
;; string SCLK to ticks which are units of encoded SCLK.
;;
cspice_sctiks, SCID, SCLTOL, toltik
;;
;; cspice_ckgpav requires encoded spacecraft clock.
;;
cspice_scencd, SCID, SCLKCH, sclkdp
cspice_ckgpav, INSTID, sclkdp, toltik, REFFRM, $
cmat, av, clkout, found
;;
;; Recall that `cmat' and `av' are the rotation and angular
;; velocity of the transformation from J2000 to the
;; spacecraft frame.
;;
if ( found ) then begin
;;
;; Display `cmat' and `av'.
;;
print, format='(A)', 'Rotation matrix:'
print, format='(3F10.6)', cmat
print, format='(A)', 'Angular velocity:'
print, format='(3F20.16)', av
;;
;; Get state transformation from J2000 to the spacecraft
;; frame.
;;
cspice_rav2xf, cmat, av, fxmat
;;
;; Display the results.
;;
print
print, format='(A)', 'State transformation matrix:'
print, format='(6F10.6)', fxmat
endif else begin
print, 'No rotation matrix/angular velocity found for ', SCLKCH
endelse
END
When this program was executed on a Mac/Intel/IDL8.x/64-bit
platform, the output was:
Rotation matrix:
-0.604984 0.796222 -0.005028
-0.784160 -0.596891 -0.169748
-0.138158 -0.098752 0.985475
Angular velocity:
0.0000032866819065 -0.0000099372638338 0.0000197597699770
State transformation matrix:
-0.604984 0.796222 -0.005028 0.000000 0.000000 0.000000
-0.784160 -0.596891 -0.169748 0.000000 0.000000 0.000000
-0.138158 -0.098752 0.985475 0.000000 0.000000 0.000000
-0.000016 -0.000012 -0.000003 -0.604984 0.796222 -0.005028
0.000013 -0.000015 -0.000010 -0.784160 -0.596891 -0.169748
-0.000008 -0.000006 -0.000002 -0.138158 -0.098752 0.985475
2) Compute a state transformation matrix from a rotation matrix
for "elementary" frame rotations of 90 degrees about the Z axis
and an angular velocity vector, convert that transformation
matrix back to a rotation matrix and an angular velocity vector
and compute the maximum value of the absolute difference between
the rotation matrices and the angular velocity vectors.
Numerical equivalence shall be expected.
Example code begins here.
PRO rav2xf_ex2
;;
;; Define an angular velocity vector:
;;
e1 = [ 1.d, 0.d, 0.d ]
;;
;; Rotation matrix for "elementary" frame rotations: 90 degrees
;; about the z axes:
;;
rz_90 = [ [ 0.d, 1.d, 0.d ], $
[-1.d, 0.d, 0.d ], $
[ 0.d, 0.d, 1.d ] ]
;;
;; The call cspice_rav2xf calculates the state transformation matrix
;; strans associated with the angular velocity vector and the
;; rotation matrix.
;;
cspice_rav2xf, rz_90, e1, strans
;;
;; cspice_xf2rav converts a state transformation to the associated
;; rotation matrix and angular velocity vector - inverting
;; the operation of cspice_rav2xf
;;
cspice_xf2rav, strans, rot, av
;;
;; Calculate the maximum value of the absolute difference between the
;; output `av' and `rot' vs the inputs `e1' and `rz_90'.
;;
print, format='(A,F15.13)', 'Maximum absolute difference ' + $
'between rotation matrices : ', $
max( max( abs(rot - rz_90) ) )
print, format='(A,F15.13)', 'Maximum absolute difference ' + $
'between angular velocities: ', $
max( max( abs(av - e1) ) )
END
When this program was executed on a Mac/Intel/IDL8.x/64-bit
platform, the output was:
Maximum absolute difference between rotation matrices : 0.0000000000000
Maximum absolute difference between angular velocities: 0.0000000000000
This routine is essentially a macro routine for converting
a rotation and angular velocity of the rotation to the
equivalent state transformation matrix.
This routine is an inverse of cspice_xf2rav.
1) No checks are performed on `rot' to ensure that it is indeed
a rotation matrix.
2) If any of the input arguments, `rot' or `av', is undefined, an
error is signaled by the IDL error handling system.
3) If any of the input arguments, `rot' or `av', is not of the
expected type, or it does not have the expected dimensions and
size, an error is signaled by the Icy interface.
4) If the output argument `xform' is not a named variable, an
error is signaled by the Icy interface.
None.
None.
ICY.REQ
ROTATION.REQ
None.
J. Diaz del Rio (ODC Space)
E.D. Wright (JPL)
-Icy Version 1.0.2, 10-AUG-2021 (JDR)
Edited the header to comply with NAIF standard. Added first code
example and created second code example from existing fragment.
Added -Parameters, -Exceptions, -Files, -Restrictions,
-Literature_References and -Author_and_Institution sections, and
extended -Particulars section.
Removed reference to the routine's corresponding CSPICE header from
-Abstract section.
Added arguments' type and size information in the -I/O section.
-Icy Version 1.0.1, 12-APR-2007 (EDW)
Edit to abstract.
-Icy Version 1.0.0, 16-JUN-2003 (EDW)
State transformation to rotation and angular velocity
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