Procedure

   void xf2rav_c ( ConstSpiceDouble   xform [6][6],
                   SpiceDouble        rot   [3][3],
                   SpiceDouble        av    [3]     ) 

Abstract

 
   This routine determines the rotation matrix and angular 
   velocity of the rotation from a state transformation matrix.
 

Required_Reading

 
   None. 
 

Keywords

 
   FRAMES 
 

Brief_I/O

 
   VARIABLE  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_Input

 
   xform       is a state transformation matrix from one frame 
               frame1 to some other frame frame2. 
 

Detailed_Output

 
   rot         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. 
 

Parameters

 
   None. 
 

Exceptions

 
   Error free. 
 
   1) No checks are performed on xform to ensure that it is indeed 
      a state transformation matrix. 
 

Files

 
   None. 
 

Particulars

 
   This 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. 
 

Examples

 
   Suppose that you wanted to determine the angular velocity 
   of the earth with respect to J2000 at a particular epoch et. 
   The following code fragment illustrates a procedure for 
   computing the angular velocity. 
 
      sxform_c ( "J2000", "IAU_EARTH", et, tsipm ) ;
 
   Now get the angular velocity by calling xf2rav_c:
 
      xf2rav_c ( tsipm, tpmi, av ); 
 

Restrictions

 
   None. 
 

Literature_References

 
   None. 
 

Author_and_Institution

 
   N.J. Bachman    (JPL)
   W.L. Taber      (JPL) 
 

Version

   -CSPICE Version 1.0.1, 12-APR-2007 (EDW) 

      Edit to abstract.
 
   -CSPICE Version 1.0.0, 18-JUN-1999 (WLT) (NJB)

Index_Entries

 
   State transformation to rotation and angular velocity 
 

Link to routine xf2rav_c source file xf2rav_c.c