rav2xf_c |

Table of contents## Procedurerav2xf_c ( Rotation and angular velocity to transform ) void rav2xf_c ( ConstSpiceDouble rot [3][3], ConstSpiceDouble av [3], SpiceDouble xform [6][6] ) ## AbstractDetermine a state transformation matrix from a rotation matrix and the angular velocity of the rotation. ## Required_ReadingROTATION ## KeywordsFRAMES ## Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- rot I Rotation matrix. av I Angular velocity vector. xform O State transformation associated with `rot' and `av'. ## Detailed_Inputrot is a rotation matrix that gives the transformation from some frame FRAME1 to another frame FRAME2. av is the angular velocity of the transformation. 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 ) ## Detailed_Outputxform is a state transformation matrix associated with `rot' and `av'. 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. ## ParametersNone. ## ExceptionsError free. 1) No checks are performed on `rot' to ensure that it is indeed a rotation matrix. ## FilesNone. ## ParticularsThis 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 xf2rav_c. ## ExamplesThe 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) The following example program uses ckgpav_c 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. /. Program rav2xf_ex1 ./ #include <stdio.h> #include "SpiceUsr.h" int main( ) { /. 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 ckgpav_c. -- The reference frame we want is J2000. ./ #define META "rav2xf_ex1.tm" #define REFFRM "J2000" #define SCLKCH "1/1465476046.160" #define SCLTOL "1.0" #define SCID -82 #define INSTID -82000 /. Local variables. ./ SpiceDouble av [3]; SpiceDouble clkout; SpiceDouble cmat [3][3]; SpiceDouble fxmat [6][6]; SpiceDouble sclkdp; SpiceDouble toltik; SpiceInt i; SpiceBoolean found; /. Load kernels. ./ furnsh_c ( META ); /. Convert tolerance from CASSINI formatted character string SCLK to ticks which are units of encoded SCLK. ./ sctiks_c ( SCID, SCLTOL, &toltik ); /. ckgpav_c requires encoded spacecraft clock. ./ scencd_c ( SCID, SCLKCH, &sclkdp ); ckgpav_c ( 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 ) { /. Display `cmat' and `av'. ./ printf( "Rotation matrix:\n" ); for ( i = 0; i < 3; i++ ) { printf( "%10.6f %9.6f %9.6f\n", cmat[i][0], cmat[i][1], cmat[i][2] ); } printf( "Angular velocity:\n" ); printf( "%20.16f %19.16f %19.16f\n", av[0], av[1], av[2] ); /. Get state transformation from J2000 to the spacecraft frame. ./ ## RestrictionsNone. ## Literature_ReferencesNone. ## Author_and_InstitutionN.J. Bachman (JPL) J. Diaz del Rio (ODC Space) W.L. Taber (JPL) E.D. Wright (JPL) ## Version-CSPICE Version 1.0.2, 16-JUL-2020 (JDR) Edited the header to comply with NAIF standard. Added complete code example based on existing example. Added ROTATION to the required readings. -CSPICE Version 1.0.1, 12-APR-2007 (EDW) Edit to abstract. -CSPICE Version 1.0.0, 18-JUN-1999 (WLT) (NJB) ## Index_EntriesState transformation to rotation and angular velocity |

Fri Dec 31 18:41:11 2021