NAME:
  occxtrack
 PURPOSE:   (one line only)
  Compute cross-track and other geometric information for an occultation
 DESCRIPTION:
 CATEGORY:
  Occultations
 CALLING SEQUENCE:
  occxtrack
 INPUTS:
  All inputs are fixed name files.
   xtrack.in   - contains general information about the occultation
                   leading and trailing blanks on a line do not matter
                   any lines after the required set are ignored
     line 1 - Name of event
     line 2 - Object code (for geteph, see ephem.pro)
     line 3 - RA of the star (sexigesimal string)
     line 4 - Dec of the star (sexigesimal string)
     line 5 - geocentric UT date and time of appulse
     line 6 - 1-sigma down-track uncertainty (in seconds)
     line 7 - 1-sigma cross-track uncertainty (in km)

   chords.dat - list of all stations, same file used for occprof
     col 1 - siteid (short string)
     col 2 - flag, 'y' means good data, 'n' means no good data
     col 3 - latitude (degrees)
     col 4 - east longitude (degrees)
     col 5 - altitude (m)
     col 6 - date of occultation (x if no occultation seen)
     col 7 - time of disappearance (x if no occultation seen)
     col 8 - time or reappearance (x if no occultation seen)
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
  FILE - name of file to read with sites.  default = sites.dat
                This can still read a chords.dat file but this feature
                   is deprecated and all usage needs to shift to the
                   new file setup.
  OUTFILE - name of file to write to, default = crosstrack.dat
  FNCONFIG - name of configuration file (overrides xtrack.in),
              the default is config.ini but if the configuration file
              is not found then operation reverts to using xtrack.in
              The minimal content of the config file must have:
   [global]
     event   - string with short ID oame of event (ex: OR20200914)
     objectid - object code (see ephem.pro)
     ora      - HH:MM:SS.sss position of occultation star at epoch of event
     odec     - +DD:MM:SS.sss position of occultation star at epoch of event
     geomid   - YYYY-MM-DD HH:MM:SS.s UT time of geocentric mid-time of event
     tsig     - 1-sigma down-track error in seconds
     xsig     - 1-sigma cross-track error in km

 OUTPUTS:
  All outputs are fixed name files.
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  Written by Marc W. Buie, Southwest Research Institute, 2020/01/31
  2020/09/28, MWB, added FILE keyword
  2021/03/10, MWB, added OUTFILE keyword
  2021/05/07, MWB, added FNCONFIG keyword
  2022/12/20, MWB, changed to use sites.dat instead of chords.dat