NAME:
  seeing
 PURPOSE:   (one line only)
  Given an astronomical image, determine the image quality (seeing).
 DESCRIPTION:
 CATEGORY:
  CCD data processing
 CALLING SEQUENCE:
  seeing,image,fwhm,objrad,nstars
 INPUTS:
  image - Array containing image to be examined.
 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.
  MINSIGNAL - minimum signal to consider when looking for sources
                 (default=0)
  MAXSIGNAL - maximum signal to conisder when looking for sources
                 (default=60000)
  NODISPLAY - Flag, if set will suppress plot and image outputs
    RADP    - Flag, if set uses a radial profile gaussian fit to determine
                  the FWHM.  This is more accurate if the seeing is gaussian
                  and well behaved.  This option will be slower and slightly
                  more prone to failure, particularly for faint sources.
 OUTPUTS:
  fwhm  - Image quality, FWHM in pixels for the image.
  objrad - Object aperture radius used to determine fwhm
  nstars - Number of stars that were averaged to get fwhm
 KEYWORD OUTPUT PARAMETERS:
  ERROR - set to 1 (true) if an error occurred, zero otherwise.  If the
            error flag is set, the return values may or may not be useful.
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  Written by Marc W. Buie, Lowell Observatory, 2004/07/03
  2005/06/28, MWB, added extra error trapping and ERROR keyword
  2008/07/23, MWB, added keyword for initial FWHM guess
  2013/07/06, MWB, added RADP keyword option
  2016/06/24, MWB, added some extra optional plot output