- Abstract
Convert a CSPICE ellipse to a center vector and two generating
vectors. The selected generating vectors are semi-axes of the
ellipse.
- Required_Reading
ELLIPSES
- Brief_I/O
Variable I/O Description
-------- --- --------------------------------------------------
ellipse I A CSPICE ellipse.
center,
smajor,
sminor O Center and semi-axes of ellipse.
- Detailed_Input
ellipse is a CSPICE ellipse.
- Detailed_Output
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].
- Parameters
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 )
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].
- Examples
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 );
- Restrictions
None.
- Exceptions
Error free.
- Files
None.
- Author_and_Institution
N.J. Bachman (JPL)
- Literature_References
None.
- Version
-CSPICE Version 1.0.0, 12-JUN-1999 (NJB)
- Index_Entries
ellipse to center and generating vectors
- Link to routine source