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

   None. 

   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. 

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

   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. 

   None. 

   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. 

   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 ); 

   None. 

   Error free. 

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

   None. 

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

   None. 

   -CSPICE Version 1.0.0, 18-JUN-1999 (WLT) (NJB)

   State transformation to rotation and angular velocity