NAME:
  loadocc
 PURPOSE:   (one line only)
  Load a set of information for an occultation
 DESCRIPTION:
 CATEGORY:
  Occultations
 CALLING SEQUENCE:
 INPUTS:
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
  FNSITES - name of the file with site location information (default=sites.dat)
               this file _must_ exist
  FNEVENTS - name of occultation events file (default=events.dat), to suppress
               reading set to an empty string
  FNXTRACK - name of occultation predition geometry file
              (default=crosstrack.dat),
              to suppress reading set to an empty string
  SHOW     - Flag, if set will generated output to the screen that shows
              a complete listing of the event information loaded, with its
              related cross-reference data.
 OUTPUTS:
  info - anonymous structure with collected information
          The only tags that are assured to exist are, nsites, nevents, and
          ntracks.  If nsites=0 then there is nothing else.  If nevents or
          ntracks is zero then the structure elements for those parts will
          not exist.  See occxtrack, rdsites, rdevents for information
          one what is in those files.  There is a tag provided (.sidx) for
          matching the "event" arrays to the site/track arrays.  For example,
          info.lat[info.sidx] will be the site latitude for each of the
          events.
 KEYWORD OUTPUT PARAMETERS:
 CONFIGURATION:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
  The file pointed to by FNSITES must exist.  All other files are optional
   as far as the reader is concerned.
 PROCEDURE:
 MODIFICATION HISTORY:
  Written by Marc W. Buie, Southwest Research Institute, 2022/12/07
  2023/01/28, MWB, fixed indexing bug in event sub-structure
  2023/02/07, MWB, change to allow a missing or empty events.dat file
  2023/02/08, MWB, added SHOW keyword
  2023/08/17, MWB, upgraded to work with new version of rdevents.pro