Procedure

   void cgv2el_c ( ConstSpiceDouble    center[3],
                   ConstSpiceDouble    vec1  [3],
                   ConstSpiceDouble    vec2  [3],
                   SpiceEllipse      * ellipse   ) 

Abstract

 
   Form a CSPICE ellipse from a center vector and two generating 
   vectors. 
 

Required_Reading

 
   ELLIPSES 
 

Keywords

 
   ELLIPSE 
   GEOMETRY 
 

Brief_I/O

 
   Variable  I/O  Description 
   --------  ---  -------------------------------------------------- 
   center, 
   vec1, 
   vec2       I   Center and two generating vectors for an ellipse. 
   ellipse    O   The CSPICE ellipse defined by the input vectors. 
 

Detailed_Input

 
   center, 
   vec1, 
   vec2           are a center and two generating vectors defining 
                  an ellipse in three-dimensional space.  The 
                  ellipse is the set of points 
 
                     center  +  cos(theta) vec1  +  sin(theta) vec2 
 
                  where theta ranges over the interval (-pi, pi]. 
                  vec1 and vec2 need not be linearly independent. 
 

Detailed_Output

 
   ellipse        is the CSPICE ellipse defined by the input 
                  vectors. 
 

Parameters

 
   None. 
 

Exceptions

 
   1)  If vec1 and vec2 are linearly dependent, ellips will be 
       degenerate.  CSPICE ellipses are allowed to represent 
       degenerate geometric ellipses. 
 

Files

 
   None. 
 

Particulars

 
   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 ) 
 

Examples

 
   1)  Find the intersecton of an ellipse with a plane.  The ellipse 
       is defined by the vectors center, vec1, and vec2.  The plane 
       is defined by the normal vector n and the constant c. 
 
          #include "SpiceUsr.h"
                    .
                    .
                    .
          /.
          Make a CSPICE ellipse.  Make a plane while we're at it. 
          ./
          cgv2el_c ( center, vec1, vec2,  &ellipse ); 
          nvc2pl_c ( n,      c,           &plane   ); 

          /.
          Find the intersection of the ellipse and plane. 
          nxpts is the number of intersection points; xpt1 
          and xpt2 are the points themselves. 
          ./
          inelpl_c ( &ellipse, &plane, &nxpts, xpt1, xpt2 );
 
 

Restrictions

 
   None. 
 

Literature_References

 
   None. 
 

Author_and_Institution

 
   N.J. Bachman   (JPL) 
 

Version

 
   -CSPICE Version 1.0.0, 05-MAR-1999 (NJB)

Index_Entries

 
   center and generating vectors to ellipse 
 

Link to routine cgv2el_c source file cgv2el_c.c