If the integer code for the reference frame is not recognized,
       SPICE(INVALIDREFFRAME) is signaled.
 
   4)  If the start time of the first record exceeds the descriptor
       begin time by more than a computed tolerance, or if the end time
       of the last record precedes the descriptor end time by more than
       a computed tolerance, the error SPICE(COVERAGEGAP) is signaled.
       See the Parameters section above for a description of the
       tolerance.
 
   5)  If the input degree `polydg' 