he origin and oriented so that
               its axes lie on the x, y and z axes. 'a', 'b', and 'c' are
               the lengths of the semi-axes that respectively point in the
               x, y, and z directions.

      viewpt   a point from which the ellipsoid is viewed. 'viewpt' must be
               outside of the ellipsoid.

               [3,1] = size(viewpt); double = class(viewpt)

   the call:

      limb = <b>cspice_edlimb</b>( a, b, c, viewpt )

   returns:

      limb   the SPICE ellipse t