define	SZ_FITTYPE	8

#  SUBSKY -- Subtract background from HSP observations
#
#  Description:
#  ------------
#  Subtract background (i.e. sky) observations from object-plus-sky
#  observations.  The background data may have been taken simultaneously
#  with the object+sky data; or the two sets may be interleaved; or
#  there may be two files of background data, one taken before and
#  one taken after the object+sky data.
#  Background subtraction may be done in one of the following ways:
#	(1) Point-by-point
#	(2) A linear fit to pairs of adjacent background observations
#	(3) A low-order curve fit to a user-specified number of background
#	    data values near the time of each object+sky observation
#	    (e.g. a quadratic fit to four background points)
#	(4) A low-order curve fit to all of the background data
#  The last option is the only one that may be used if there are two
#  (or more) files of background data.
#
#  Input files must be count rate or count rate per unit area.  They can
#  not be counts because this task does compensate for possible different 
#  integration times between object and background files.
#
#  Date		Author			Description
#  ----		------			-----------
#  05-Dec-1985	C. D. Biemesderfer      Original module
#  23-Mar-1990  J.-C. Hsu		rewrite in SPP
#------------------------------------------------------------------------------

procedure subsky ()

pointer	fin, fsky, finmask, fskymask, fout, foutmask	
				# file template pointers
int	nfin			# number of files in input template
char	fittype[SZ_FITTYPE]	# method of fitting
int	order			# order of the fitting polynomial
int	nptsfit			# number of sky points used to fit
int	nskyfiles		# number of sky files per data file
bool	maskflag		# is input mask file specified?
bool	bmaskflag		# is background mask file specified?
#==============================================================================
begin

	# announce start of the task
	call printf ("*** SUBSKY - Version 1.0 ***\n")

	# get input parameters
	call subsky_get (fin, fsky, fout, finmask, fskymask, foutmask, nfin, 
			fittype, order, nptsfit, nskyfiles, maskflag, bmaskflag)

	# do the background subtraction
	call subsky_do (fin, fsky, fout, finmask, fskymask, foutmask, nfin, 
			fittype, order, nptsfit, nskyfiles, maskflag, bmaskflag)

	# close file templates
	call imtclose (fin)
	call imtclose (fout)
	call imtclose (fsky)
	call imtclose (fskymask)
	call imtclose (finmask)
	call imtclose (foutmask)

	# announce completion of task
	call printf ("background subtraction task completed with no error\n")
end