 computed using the
                         method indicated by 'abcorr'.

                         [1,1] = size(surf(i).trgepc)
                         double = class(surf(i).trgepc)

                         'trgepc' is expressed as seconds past J2000 TDB.

               obspos    the vector from the center of the target body at
                         epoch 'trgepc' to the observer at epoch 'et'.
                         'obspos' is expressed in the target body-fixed
                         referenc