NAME:
  occshowgrid
 PURPOSE:   (one line only)
  Show a grid of postage stamp images from an occultation dataset
 DESCRIPTION:
 CATEGORY:
  Occultations
 CALLING SEQUENCE:
  occshowgrid,team,nx,ny,dw
 INPUTS:
  team - String with the name of the team/dataset to read
  nx   - width of image grid
  ny   - height of image grid
  dw   - half-width of the thumbnail to extract
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
  HISIG - sigma level for upper stretch threshold (low is -3 sigma),
             (default = 5)
  ACTUAL - Flag, if set, use the D&R times (from chords.dat) to establish
             the reference time, otherwise just used the prediction
             (from crosstrack.dat).
  WINDOW - direct graphics window to use for display (default=0)
  SAVEPNG - Flag, if set, causes the display to be saved to a .png file.
              The file name will be [team]_grid.png.
  POS     - Optional two element vector with the position of the target [x,y]
            If supplied will bypass trying to get this from the database.
  LCFILE  - To bypass using the database for the PSF reductions, supply
              a lightcurve file as written by occproc.pro.  It's up to
              you to provide a file that is consistent with the team
              provided.  This will use the x,y position in the file unless
              you also provide the POS keyword.
  ZF      - zoom factor for thumbnails, default=2
 OUTPUTS:
 KEYWORD OUTPUT PARAMETERS:
 CONFIGURATION:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  Written by Marc W. Buie, Southwest Research Institute, 2020/09/23
  2022/01/25, MWB, Added code to handle SAVEPNG keyword optional input
                    argument.  Added POS and LCFILE keywords.