void el2cgv_c ( ConstSpiceEllipse * ellipse,
SpiceDouble center[3],
SpiceDouble smajor[3],
SpiceDouble sminor[3] )
Convert a CSPICE ellipse to a center vector and two generating
vectors. The selected generating vectors are semiaxes of the
ellipse.
ELLIPSES
ELLIPSE
GEOMETRY
Variable I/O Description
  
ellipse I A CSPICE ellipse.
center,
smajor,
sminor O Center and semiaxes of ellipse.
ellipse is a CSPICE ellipse.
center,
smajor,
sminor are, respectively, a center vector, a semimajor
axis vector, and a semiminor 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.
Error free.
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 semimajor 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 semiminor
axis is an analogous vector of smallest possible magnitude. The
semimajor and semiminor axes are orthogonal to each other. If
smajor and sminor are choices of semimajor and semiminor 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 semiaxes 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.
None.
N.J. Bachman (JPL)
CSPICE Version 1.0.0, 12JUN1999 (NJB)
ellipse to center and generating vectors
