r example both 'MOON' and '301' are
               legitimate strings that indicate the moon is the
               observer.

               [1,c6] = size(obsrvr); char = class(obsrvr)

                  or

               [1,1] = size(obsrvr); cell = class(obsrvr)

               `obsrvr' may be not be identical to `target'.

      spoint   is a surface point on the target body, expressed in
               Cartesian coordinates, relative to the body-fixed
               target frame designated by `fixref'.