Convert a CSPICE ellipse to a center vector and two generating vectors. The selected generating vectors are semi-axes of the ellipse.
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].
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 );
N.J. Bachman (JPL)
-CSPICE Version 1.0.0, 12-JUN-1999 (NJB)
ellipse to center and generating vectors