el2cgv_c

Index Page el2cgv_c
A B C D E F G H I J K L M N O P Q R S T U V W X
Procedure Abstract Required_Reading Keywords Brief_I/O Detailed_Input | Detailed_Output Parameters Exceptions Files Particulars Examples | Restrictions Literature_References Author_and_Institution Version Index_Entries
#### Procedure
       void el2cgv_c ( ConstSpiceEllipse   * ellipse,
                       SpiceDouble           center[3],
                       SpiceDouble           smajor[3],
                       SpiceDouble           sminor[3]  )
#### 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
#### Keywords
       ELLIPSE
       GEOMETRY
#### 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.
#### Exceptions
       Error free.
#### 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 )

       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.
#### Literature_References
       None.
#### Author_and_Institution
       N.J. Bachman   (JPL)
#### Version
       -CSPICE Version 1.0.0, 12-JUN-1999 (NJB)
#### Index_Entries
       ellipse to center and generating vectors
#### Link to routine el2cgv_c source file el2cgv_c.c

    Thu Apr 16 08:58:01 2009