Form a CSPICE ellipse from a center vector and two generating vectors.
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.
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.
ellipse is the CSPICE ellipse defined by the input vectors.
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 )
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 );
1) If vec1 and vec2 are linearly dependent, ellips will be degenerate. CSPICE ellipses are allowed to represent degenerate geometric ellipses.
N.J. Bachman (JPL)
-CSPICE Version 1.0.0, 05-MAR-1999 (NJB)
center and generating vectors to ellipse