m number of intervals to return in 'result'.
               Note: this value should equal at least the number of expected
               intervals. Recall two double precision values define
               an interval.

               [1,1] = size(nintvls); int32 = class(nintvls)

   the call:

      result = <b>cspice_gfrfov</b>( inst, raydir, rframe, abcorr, ...
                              obsrvr, step, cnfine, nintvls)

   returns:

      result   the SPICE window of intervals, contained within the
    