                 Find the rotation matrix from the ray's reference
                 frame at the time the photons were received (etrec)
                 to IAU_MARS at the time the photons were emitted
                 (etemit).
                 ./
                 <b>pxfrm2_c</b> ( obsref, &quot;IAU_MARS&quot;, etrec, etemit, rotate );

                 /.     
                 Look up the radii values for Mars.
                 ./
                 <a href="bodvrd_c.html">bodvrd_c</a> ( &quot;MARS&quot;, &