 DSK
       segment is determined from the `center' member of the segment's
       DSK descriptor.

   10) If the segment associated with the input DLA descriptor is not
       of data type 2, the error SPICE(WRONGDATATYPE) is signaled.

   11) Use of transmission-style aberration corrections is not
       permitted.  If abcorr specified such a correction, the 
       error SPICE(NOTSUPPORTED) is signaled.

   12) The observer is presumed to be outside the target body; no
       checks are made to verify th