`trgepc'.

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

               The components of `srfvec' are given in units of km.

               One can use the function norm to obtain the
               distance between the observer and `spoint':

                  dist = norm( srfvec );

               The observer's position `obspos', relative to the
               target body's center, where the center's position is
               corrected for aberration effects as indicated by
             