IRAF help page for package noao.digiphot.apphot, program fitsky

• image
• coords =
• output = default
• plotfile =
• datapars =
• fitskypars =
• interactive = yes
• radplots = no
• verify = yes
• update = no
• verbose = no
• graphics = stdgraph
• display = stdimage
• icommands =
• gcommands =

fitsky image

image

coords =

output = default

plotfile =

datapars =

fitskypars =

interactive = yes

radplots = no

verify = yes

update = no

verbose = no

graphics = stdgraph

display = stdimage

icommands =

gcommands =

FITSKY computes accurate sky values for a set of objects in the IRAF image image, whose coordinates are listed in the text file coords or are marked on the terminal interactively with the image cursor, and writes the computed sky values to the text file output.

FITSKY can be run either interactively or in batch mode by setting the parameter interactive. In interactive mode starting x and y positions can either be read directly from the image cursor or read from the text file coords. The user can adjust the parameters of the fitting algorithm until a satisfactory parameter set is found, change objects interactively or query for the next object in the list, and finally fit the entire coordinate list with that set of parameters. In batch mode the estimated positions can be read from the text file coords or the image cursor parameter icommands can be redirected to a text file containing a list of cursor commands.

The following cursor commands are currently available.

	Interactive Keystroke Commands
?	Print help
:	Colon commands
v	Verify the critical parameters
w	Save the current parameters
d	Plot radial profile of current star 
i	Interactively set parameters using current star
f	Fit sky for current star
spbar	Fit sky for current star, output results
m	Move to next star in coordinate list
m	Fit sky for next star in coordinate list, output results
l	Fit sky for remaining stars in coordinate list, output results
e	Print error messages
r	Rewind the coordinate list
q	Exit task
        Colon commands
:show	[data/sky]	List the parameters
:m [n]	Move to the next [nth] star in coordinate list
:n [n]	Fit sky to next [nth] star in coordinate list, output results
	Colon Parameter Editing Commands
# Image and file name parameters
:image		[string]	Image name
:coords		[string]	Coordinate file name
:output 	[string]	Output file name
# Data dependent parameters
:scale		[value]		Image scale (units per pixel)
:fwhmpsf	[value]		Full width half maximum PSF (scale units)
:emission	[y/n]		Emission feature (y), absorption (n)
:sigma		[value]		Standard deviation of sky (counts)
:datamin	[value]		Minimum good pixel value (counts)
:datamax	[value]		Maximum good pixel value (counts)
# Noise parameters
:noise		[string]	Noise model (constant|poisson)
:gain		[string]	Gain image header keyword
:ccdread	[string]	Readout noise image header keyword
:epadu		[value]		Gain (electrons per adu)
:readnoise	[value]		Readout noise (electrons)
# Observations parameters
:exposure	[string]	Exposure time image header keyword
:airmass	[string]	Airmass image header keyword
:filter		[string]	Filter image header keyword
:obstime	[string]	Time of observation image header keyword
:itime		[value]		Exposure time (time units)
:xairmass	[value]		Airmass value (number)
:ifilter	[string]	Filter id string
:otime		[string]	Time of observation (time units)
# Sky fitting algorithm parameters
:salgorithm	[string]	Sky fitting algorithm 
:skyvalue	[value]		User supplied sky value (counts)
:annulus 	[value]		Inner radius of sky annulus (scale units)
:dannulus	[value]		Width of sky annulus (scale units)
:khist		[value]		Sky histogram extent (+/- sky sigma)
:smooth		[y/n]		Lucy smooth the sky histogram 
:binsize	[value]		Resolution of sky histogram (sky sigma)
:smaxiter	[value]		Maximum number of iterations
:sloclip	[value]		Low side clipping factor (percent)
:shiclip	[value]		High side clipping factor (percent)
:snreject	[value]		Maximum number of rejection cycles
:sloreject	[value]		Low side pixel rejection limits (sky sigma)
:shireject	[value]		High side pixel rejection limits (sky sigma)
:rgrow		[value]		Region growing radius (scale units)
# Marking and plotting parameters
:mksky		[y/n]		Mark sky annuli on the display
:radplot	[y/n]		Plot radial profile of sky pixels
The following commands are available from within the interactive setup menu.
                      Interactive Fitsky Setup Menu
	v	Mark and verify the critical parameters (a,d,s)
	s	Mark and verify the standard deviation of the sky
	l	Mark and verify the minimum good data value
	u	Mark and verify the maximum good data value
	a	Mark and verify the inner radius of the sky annulus
	d	Mark and verify the width of the sky annulus
	g	Mark and verify the region growing radius

A brief description of the data dependent parameters and the sky fitting parameters can be found in the online manual pages for the DATAPARS and FITSKYPARS tasks. A full description of the algorithms can be found in the document Specifications for the Apphot Package.

In interactive mode the following quantities are printed on the standard output as each object is measured.

    image  xinit  yinit  msky  stdev  sskew  nsky  nsrej  error

In both interactive and batch mode full output is written to the text file output. At the beginning of each file is a header listing the current values of the parameters when the first stellar record was written. These parameters can be subsequently altered. For each star measured the following record is written.

    image  xinit  yinit  id  coords  lid
	msky  stdev  sskew  nsky  nsrej  sier  error

Image and coords are the name of the image and coordinate file respectively. Id and lid are the sequence numbers of stars in the output and coordinate files respectively. Sier and error are the error code and accompanying error message respectively. Xinit and yinit are the center coordinates of the sky annulus in pixels. Msky, stdev and sskew are the sky value, standard deviation and skew respectively. Nsky and nsrej are the number of sky pixels used and the number of sky pixels rejected respectively.

If all goes well during the sky fitting process then the error code sier will be 0. Non-zero values of sier flag the following error conditions.

	0         # No error
	201       # There are no sky pixels in the sky annulus
	202       # Sky annulus is partially off the image
	203       # The histogram of sky pixels has no width
	204       # The histogram of sky pixels is flat or concave
	205       # There are too few points for a good sky fit
	206       # The sky fit is singular
	207       # The sky fit did not converge
	208       # The graphics stream is undefined
	209       # The file of sky values does not exist
	210       # The sky file is at EOF
	211       # Cannot read the sky value correctly
	212       # The best fit parameters are non-physical

1. Compute the sky statistics for a few stars in N4147 using the display and the image cursor. Setup the task parameters using the interactive setup menu defined by the i key command and a radial profile plot.

	ap> set stdimcur = stdimage
	... define the image cursor
	ap> display n4147 1 fi+
	... display the image
	ap> fitsky n4147 
	... type ? for an optional help page
	... move the image cursor to a star
	... type i to enter the interactive setup menu
	... enter maximum radius in pixels of the radial profile
	... set the annulus, dannulus, and sigma
	    using the graphics cursor and the stellar radial profile plot
	... typing  leaves everything at the default value
	... type the w key to save the parameters in the parameter files
	... type the v key to verify critical parameters
	... move the image cursor to the stars of interest and tap
	    the space bar
	... the output will appear in n4147.sky.1

2. Compute the sky statistics for a few stars in M92 using a contour plot and the graphics cursor. Setup the task parameters using the interactive setup menu defined by the i key command.

	ap> set stdimcur = stdgraph
	... define the image cursor to be the graphics cursor
	ap> contour m92 >G m92.plot1
	... store the contour plot of m92 in the file m92.plot
	ap> fitsky m92 display=stdgraph
	... type ? for an optional help page
	... type :.read m92.plot1 to load the contour plot on the screen
	... move graphics cursor to a star
	... type i to enter the interactive setup menu
	... enter maximum radius in pixels of the radial profile
	... set the annulus, dannulus, and sigma
	    using the graphics cursor and the stellar radial profile plot
	... typing  leaves everything at the default value
	... type the w key to save the parameters in the parameter files
	... type the v key to verify the parameters
	... retype :.read m92.plot1 to reload the contour plot
	... move the graphics cursor to the stars of interest and tap
	    the space bar
	... a one line summary of the sky statistics will appear on the
	    standard output for each star measured
	... full output will appear in the text file m92.sky.1 

3. Setup and run FITSKY interactively on a list of objects, using a contour plot as the image display and the parameters defined and saved in example 1.

	ap> set stdimcur = stdgraph
	... define the image cursor to be the graphics cursor
	ap> contour m92
	... adjust plot parameters until the contour plot is satisfactory
	ap> =gcur
	... enter cursor mode
	... type :.write m92.plot2 to save the plot in a metacode file
	... type any key to quit cursor mode
	ap> daofind m92 
	... make a coordinate list
	... the output will appear in the text file m92.coo.1
	ap> fitsky m92 coords=m92.coo.1 display=stdgraph
	... type ? for an optional help menu
	... type :.read m92.plot2 to read in the contour plot
	... move the graphics cursor to the stars and tap space bar
				or
	... use m, :m and/or n, :n, l, r commands to measure objects in the
	    coordinate list
	... a one line summary of results will appear on the standard output
	    for each star measured
	... the output will appear in m92.sky.2 ...

4. Run FITSKY in batch mode using the coordinate file and the previously saved parameters. Verify the critical parameters.

	ap> fitsky m92 coords=m92.coo.1 verify+ inter-
	... output will appear in m92.sky.3

5. Run FITSKY in batch mode using the coordinate file and the previously saved parameters. The task can be submitted to the background by appending an ampersand to the command line listed below. Remember to turn the verify switch off in that case.

	ap> fitsky m92 coords=m92.coo.1 inter- verify-
	... output will appear in m92.sky.4

6. Run FITSKY interactively on the Sun workstation without the use of the IMTOOL window using only a coordinate list and the current set of parameters as input.

	ap> set stdimcur = text
	... set the image cursor to the standard input
	ap> fitsky m92 coords=m92.coo.2
	... type ? for optional help
	... type :m 3 to set the initial coordinates to those of the
	    third star in the list
	... type i to enter the interactive setup menu followed by v to
	    get the default menu
	... enter maximum radius in pixels of the radial profile
	... set the sigma, inner radius of the sky annulus, and the
	    width of the sky annulus using the graphics cursor and the stellar
	    radial profile plot
	... typing  after the prompt leaves the parameter at its default
	    value
	... type r to rewind the coordinate list
	... type l to measure all the stars in the coordinate list
	... a one line summary of the answers will appear on the standard
	    output for each star measured
	... full output will appear in the text file m92.ctr.5 

It is currently the responsibility of the user to make sure that the image displayed in the frame is the same as that specified by the image parameter.

Commands which draw to the image display are currently disabled. The TVMARK task in the proto package can be used to draw simple marks on the display. All the APPHOT marking commands will however function if a contour plot is used in lieu of the image display.

Users should not be confused by the normally enabled markcur option in the SUN/IMTOOL setup window. This feature is under the control of the IMTOOL window and the APPHOT package has no control over it.

datapars, fitskypars, phot, polyphot, radprof,