 pixels:  the boresight and one along the boundary of
         the field of view.
 
         Assumptions:
 
            1)  The light times from the surface points in the camera's
                field of view to the camera are equal.
 
            2)  The camera offset from the center of gravity of the
                spacecraft is zero. If the data are more accurate
                and precise, this assumption can be easily discarded.
 
            3)  An ellipsoid shape model for the target body is
     