Convert a CSPICE ellipse to a center vector and two generating 
   vectors.  The selected generating vectors are semi-axes of the 
   ellipse. 

   ELLIPSES 

   Variable  I/O  Description 
   --------  ---  -------------------------------------------------- 
   ellipse    I   A CSPICE ellipse. 
   center, 
   smajor, 
   sminor     O   Center and semi-axes of ellipse. 

   ellipse        is a CSPICE ellipse. 

   center, 
   smajor, 
   sminor         are, respectively, a center vector, a semi-major 
                  axis vector, and a semi-minor axis vector that 
                  generate the input ellipse.  This ellipse is the 
                  set of points 

                     center + cos(theta) smajor + sin(theta) sminor 

                  where theta ranges over the interval (-pi, pi]. 

   None. 

   CSPICE ellipses serve to simplify calling sequences and reduce 
   the chance for error in declaring and describing argument lists 
   involving ellipses. 

   The set of ellipse conversion routines is 

      cgv2el_c ( Center and generating vectors to ellipse ) 
      el2cgv_c ( Ellipse to center and generating vectors ) 

   A word about the output of this routine:   the semi-major axis of 
   an ellipse is a vector of largest possible magnitude in the set 

      cos(theta) vec1  +  sin(theta) vec2, 

   where theta is in the interval (-pi, pi].  There are two such 
   vectors; they are additive inverses of each other. The semi-minor 
   axis is an analogous vector of smallest possible magnitude.  The 
   semi-major and semi-minor axes are orthogonal to each other.  If 
   smajor and sminor are choices of semi-major and semi-minor axes, 
   then the input ellipse can also be represented as the set of 
   points 


      center + cos(theta) smajor + sin(theta) sminor 

   where theta ranges over the interval (-pi, pi]. 

   1)  Find the semi-axes of the limb of an ellipsoid. 

          #include "SpiceUsr.h"
                  .
                  .
                  .
          /.
          Our viewing location is viewpt.  The radii of the 
          ellipsoid are a, b, and c. 
          ./
          edlimb_c ( a, b, c, viewpt, &limb );

          el2cgv_c ( &limb, center, smajor, sminor ); 

   None. 

   Error free. 

   None. 

   N.J. Bachman   (JPL) 

   None. 

   -CSPICE Version 1.0.0, 12-JUN-1999 (NJB)

   ellipse to center and generating vectors