xf2rav_c |

Table of contents## Procedurexf2rav_c ( Transform to rotation and angular velocity) void xf2rav_c ( ConstSpiceDouble xform [6][6], SpiceDouble rot [3][3], SpiceDouble av [3] ) ## AbstractDetermine the rotation matrix and angular velocity of the rotation from a state transformation matrix. ## Required_ReadingROTATION ## KeywordsFRAMES ## Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- xform I is a state transformation matrix. rot O is the rotation associated with `xform'. av O is the angular velocity associated with `xform'. ## Detailed_Inputxform is a state transformation matrix from one frame FRAME1 to some other frame FRAME2. ## Detailed_Outputrot is a rotation 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 ) The components of `av' are given relative to FRAME1. ## ParametersNone. ## ExceptionsError free. 1) No checks are performed on `xform' to ensure that it is indeed a state transformation matrix. ## FilesNone. ## ParticularsThis routine is essentially a macro routine for converting state transformation matrices into the equivalent representation in terms of a rotation and angular velocity. This routine is an inverse of the routine rav2xf_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) Suppose that you wanted to determine the angular velocity of the Earth body-fixed reference frame with respect to J2000 at a particular epoch ET. The following code example illustrates a procedure for computing the angular velocity. Use the meta-kernel shown below to load the required SPICE kernels. KPL/MK File name: xf2rav_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 --------- -------- earth_720101_070426.bpc Earth historical binary PCK naif0012.tls Leapseconds \begindata KERNELS_TO_LOAD = ( 'earth_720101_070426.bpc', 'naif0012.tls' ) \begintext End of meta-kernel Example code begins here. /. Program xf2rav_ex1 ./ #include <stdio.h> #include "SpiceUsr.h" int main( ) { /. Local parameters. ./ #define META "xf2rav_ex1.tm" #define UTCSTR "2005-OCT-10 16:00:00" /. Local variables. ./ SpiceDouble av [3]; SpiceDouble et; SpiceDouble ftmtrx [6][6]; SpiceDouble rot [3][3]; SpiceInt i; /. Load SPICE kernels. ./ furnsh_c ( META ); /. Convert the input time to seconds past J2000 TDB. ./ str2et_c ( UTCSTR, &et ); /. Get the transformation matrix from J2000 frame to ITRF93. ./ sxform_c ( "J2000", "ITRF93", et, ftmtrx ); /. Now get the angular velocity by calling ## 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, 19-MAY-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 18:41:15 2021