NAME:
  fseeing
 PURPOSE:   (one line only)
  Collect and maintain seeing information for a group of images
 DESCRIPTION:
 CATEGORY:
  CCD data processing
 CALLING SEQUENCE:
  fseeing,fnlist
 INPUTS:
  fnlist - List of image files that should appear in the data file
             This should not include any directory path information, use
             the PATH keyword for that.
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
  FWHMGUESS - Initial guess of the FWHM in the image.  Default=3.  If this
                 is significantly smaller than the actual seeing you will
                 get an answer that is much too small.  The penalty for
                 guessing a larger than optimal value appears to be weak.
  SKYTHRESH - minimum signal to consider when looking for sources, this
                 number sets the threshold to be this many sigma above the
                 mean sky level (default=5)
  MAXSIGNAL - maximum signal to conisder when looking for sources
                 (default=60000)
  DISPLAY   - Flag, if set will show plot and image outputs (this is usually
                 not a good idea)
  OUTFILE   - Name of the file for saving the data (default is seeing.dat)
  PATH      - Directory where the images are to be found.  Default is the
                 current directory.
  KEYFILE - header keyword correspondence file (see loadkeys.pro)
 OUTPUTS:
 KEYWORD OUTPUT PARAMETERS:
  results - anonymous structure with the data from the seeing.dat file.
             tags are:
              fn     - list of file names (alphabetical order)
              jd     - Julian date mid-time of the image
              fwhm   - estimated seeing for each image [pixels]
              objrad - Object radius used
              nstars - Number of sources used to find fwhm
              err    - Flag, 1 if there was an error with this entry
              nfiles - number of files (length of all these vectors)
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  2010/09/17 - Written by Marc W. Buie, Southwest Research Institute