Table of Contents

Introduction to the Serial Stamp Collecting Pipeline

• to re-arrange the data gathered by the Data Acquisition system (DA), which correspond to a given camera read-out time, to the information pertaining to some area of the sky, and
• to produce postage stamps to be used with the Postage Stamp Pipeline.

The on-line Data Acquisition (DA) system reads out each CCD chip in the imaging camera simultaneously, and groups together data (e.g. quartiles) from all the images, which are sometimes referred to as frames, into a Gang file. Since it takes about 10 minutes for a star to drift across the focal plane and trail over each CCD chip, the data in a Gang file correspond to the same read-out time, rather than to the same area of sky. The SSC re-arranges this data and produces a new Fang file, which looks very much like a Gang file, but has information for the same area of sky, a field, in each passband all together. Additionaly, the SSC pipeline is used to read raw photometric images from tape, and to write them as idR files to disk.

The downstream photometric pipeline is divided into two smaller pipelines, the Postage Stamp Pipeline (PSP), and Frames Pipeline. Frames Pipeline operates on a frame by frame basis (the photometric data stream from each CCD in the photometric array is cut into frames of 2048 x 1362 pixels). The quantities such as the point spread function, the sky brightness, and the flat field and bias vectors which are not local quantities, but are determined as a function of time, are determined by the PSP.

The PSP uses information form Fang files to calculate the sky brightness, and the flat field and bias vectors. To determine the point spread function (PSF), it uses small regions, called postage stamps, which are cut out from large image frames by the SSC pipeline, and also written to Fang files. Various types of postage stamps, and details of the cutting procedure are described in section Algorithms .

Serial Stamp Collecting Pipeline Inputs

• Processing plan and tunable parameters
• koCat file with catalog of bright stars
• Information on CCD chips
• idGang files with quartile data
• idR photometric image files

• Processing plan and tunable parameters
  • scPlan.par: Processing plan to control the pipeline. Each plan targets the data for one imaging run and from one column in the imaging array.
  • scParam.par: Tunable software parameters.

• koCat*.fit file with input catalog of known objects overlapping run being processed, and used to figure out the locations of bright stars. Each entry must contain at least three fields: some sort of magnitude upon which stars will be selected, and the survey great circle coordinates (mu and nu), appropriate for this run's node and inclination. Note that since the node and inclination of scans over different strips are not the same, this catalog must be re-generated for each run.

• Information on CCD chips These files are produced by the DA system, and are changed seldom. Each observing report is accompanied by each of these files, specifying which CCD configurations, calibrations and bad pixels apply for that night's observing.
  • opConfig*.par: CCD configuration file which specifies the readout characteristics (number of amplifiers and location of overscan columns) for all chips. The SSC pipeline needs this information to figure out how many amplifiers are used on each chip, where the bias and overscan information is placed, and where photons from the sky actually hit the chip.
  • opECalib*.par: CCD calibration file which specifies the electronic characteristics (read noise, gain, full-well, and bias level). The SSC pipeline needs this information when calculating the position, width, and amplitude of stars.
  • opBC*.par: CCD bad pixel file which specifies the location of bad pixels. The SSC pipeline needs this information to eliminate from further consideration any star which is too close to a bad area on the chip. "Too close" is quantified by an input parameter specified in scParam.par file.
  • opCamera*.par: a table that describes the layout of the dewars and chips inside the imaging camera. The SSC pipeline needs this information to predict where a star will fall in the imaging camera, given some position of the boresight.

• idGang*.fit files with quartile data. These files are produced by the on-line DA system, and contain postage stamps, measured parameters for each object cut out as a stamp, and quartiles on a frame-by-frame (not field-by-field) basis. The SSC ignores all the postage stamps in a Gang file. It also ignores all the measured parameters for stars on photometric frames. However, it does use the parameters measured for each astrometric postage stamp, and it also makes use of the quartiles. Note that astrometric Gang files have an 'r' in their name (e.g. idGang-000581-r7-0004.fit), while photometric Gang files have a 'c' (e.g. idGang-000581-c1-0004.fit).

• idR*.fit photometric image files containing a raw image from one of the photometric chips. There are no files of this type needed if the user chooses to reduce an astrometric bridge column. These files can be provided to the SSC either on disk, or on tape. In the latter case, the SSC actually produces idR files by reading raw photometric images from tape, and writing them as idR files to disk.

Serial Stamp Collecting Pipeline Outputs

There are two main ways one can run the SSC: simply to read images from tape and write onto disk, or to read and process Gang files, images, etc. If you set the writePhotomOnly keyword in the scPlan.par file to 1, then the SSC will do nothing but read photometric images from tape and write them to disk. In that case, the only outputs are FITS images idR*.fit. Assuming that writePhotomOnly is set to 0, the SSC produces the following output:

• scFang*.fit: These files contain data quartiles and 65x65 stamps cut out by SSC for each frame separately. The photometric postage stamps are placed into the scFang file in their original, raw, un-flattened state, even if the SSC performed some sort of flatfielding before measuring their centers. However, it is possible for downstream pipelines to exactly reproduce the flatfielding performed by the SSC, because the SSC places the flatfield and bias values it used on each chip into these files.
• scWingList*.par: A list of 200x200 stamps (bright stars). It tabulates the row, col and magnitude (from the koCat known objects catalog), and acts an an index to scWing*.fit files on disk.
• scWing*.fit: 200x200 postage stamps (several per camera column and run) used to determine extended PSF wings. For each star there are 5 files created (one for each filter).
• scFrameList*.par: A list of whole frames, cut out by SSC, which contain a very bright star. It tabulates the row, col and magnitude (from the koCat known objects catalog), and acts an an index to scFrame*.fit files on disk.
• scFrame*.fit: One or two raw frames per camera column and run containing at least one very bright star (brighter than ~8 mag).
• scDiag*.par: Diagnostic output produced during the run. The file consists of a header and a set of data lines listing the following information for each field:
  • field number.
  • number of "wing stars" cut out in this frame (the plan is to get several of these per hour, so maybe one every 10-30 fields).
  • number of "frame stars" cut out in this frame (the plan is to get only 1 or 2 of these per night = per run).
  • number of stars detected in leading astrometric chip.
  • number of stars matched between leading and trailing astrometric chips
  • number of stars found in both astrometric chips, and which, when cut out of the corresponding photometric chips, pass all the "validity" tests (such as having a certain amplitude or size). If this is an astrometric "bridge" column, this number will be 0.
  • mean difference, in pixels, between the row positions of stars in the leading and trailing astrometric chips.
  • mean difference, in pixels, between the column positions of stars in the leading and trailing astrometric chips.
  • bias value on the left-hand amplifier of the r'-band photometric chip. If this is an astrometric "bridge" column, this number will be 0.
  • bias value on the right-hand amplifier of the r'-band photometric chip. If this is an astrometric "bridge" column, this number will be 0.
  • median value of column 100 on the r'-band photometric chip. If this is an astrometric "bridge" column, this number will be 0.
  The last three quantities may provide some quick notice that something is very wrong with one of the chips. The choice of column 100 in the r'-band chip is completely arbitrary, but at least likely to be a column which is exposed to light.

Serial Stamp Collecting Pipeline Algorithms

As already said in Introduction, the main SSC pipeline tasks are to rearrange data from files corresponding to a given read-out time to files containing data for a given area on sky, and to produce postage stamps. This section describes these steps in more details. Names printed in typeset font are input parameters specified by user in scPlan.par and scParam.par files.

• Producing Fang from Gang files
• Cutting postage stamps
• Cutting wing and frame stamps
• A note on handling photometric image files

Producing Fang files from Gang files

The on-line DA system reads out each CCD chip in the imaging camera simultaneously, and groups together data (e.g. quartiles) from all the images read out at one time into a Gang file. Since it takes about 10 minutes for a star to drift across the focal plane and trail over each CCD chip, the data in a Gang file do not correspond to the same area of sky. For example, the layout of the imaging camera shows that a star which appears in camera column 2 will first drift across the leading astrometric chip (number 72), then the r'-band chip (12), then the i'-, u'-, z'- and g'-band chips (22-52), and finally leave by moving across the trailing astrometric chip (82). The way the on-line DA arranges things, this star would appear in 7 different Gang files; for example,

   The leading  astrometric detection in Gang file 0020
   The r'-band              detection in Gang file 0023
   The i'-band              detection in Gang file 0025
   The u'-band              detection in Gang file 0027
   The z'-band              detection in Gang file 0029
   The g'-band              detection in Gang file 0031
   The trailing astrometric detection in Gang file 0033

One of the primary purposes of the SSC is to re-arrange the information gathered by the DA so that all the data pertaining to some area of the sky is collected into a single file. This Fang file therefore looks very much like a Gang file, but has information on stars in each passband (and astrometric chip) all together. To continue the example shown above, the Fang file for field 23 would contain data from each of the detections of the same star.

Cutting postage stamps

1) Find stars appearing on both astrometric chips. The positions are taken from astrometric Gang files. Matching is controlled by am_match_diff parameter which specifies a maximal distance in pixels along the row and column directions (not a true geometric distance) for two astrometric chip detections to be considered a match.

2) Discard stars which are too close to defects. Every star closer than bc_distance to a known chip defect is ignored.

3) Find the above stars on photometric images. For each chip in a camera column (i.e. for each filter), the coordinates of stamps are calculated from the positions in the leading astrometric chip and known chip-to-chip astrometric transformations.

4) Cut out stamps from photometric images. Normally, the pipeline cuts out postage stamps for stars in the photometric chips based solely upon predictions of their positions from the astrometric chips; however, if the user sets st_recenter_boxsize to a value greater than 0, a stamp is cut out at the predicted position, then its intensity-weighted first moment of pixel values is calculated (for pixels in a box with st_recenter_boxsize half-length, centered at the stamp), and then the stamp is re-cut based on the new position.

5) Discard stars which are too close to defects. Every star closer than bc_distance to a known chip defect is ignored.

6) Measure star parameters. In order to avoid any systematic differences between the positions of astrometric detections (which are measured by the on-line DA) and instances of the same stars on the photometric chips (which are measured by SSC), the SSC links in a routine called atDACentroidFind from ASTROTOOLS to perform the calculations of the center, width, peak, and integrated brightness of stars. It convolves the stamp with a gaussian of width st_conv_sigma before calculating those quantities. The results aren't very sensitive to the value of st_conv_sigma, but it should be comparable to the width of a gaussian model of the PSF.

SSC can perform these calculations on postage stamps which are

• in their raw form, or
• bias-subtracted (using ASTROLINE estimates of the bias) and flatfielded using a fixed vector for each chip, or
• bias-subtracted (using ASTROLINE estimates of the bias) and flatfielded using a vector determined from the quartiles of all data values on a single frame.

The sk group of parameters control the manner in which the sky value is calculated for each photometric postage stamp. Only pixels lying within sk_edge_npix pixels of an edge of the stamp are considered; that set of values is subjected to sk_clip_niter iterations of a sigma-clipping technique, in which the mean and standard deviation are calculated, and values more than sk_clip_nsigma stdev from the mean are discarded. The mean value of the final iteration is taken to be the sky for that stamp.

7) Mark stars with "bad" parameters. The ds group of parameters serve to dis-qualify certain photometric stamps. Those whose measured parameters fail to fall within the given ranges for radius or peak value, are marked as "bad". If the user sets the ds_xxx_delete parameter(s) to 1, then stars which fail the xxx test will be deleted from the list of valid postage stamps. Stamps are checked only in passbands listed in ds_filterlist, so by leaving this list empty, one allows all stars to pass through.

Cutting wing and frame stamps

The wing and frame stars are so bright that they ought to have perceptible wings extending outwards for many arcseconds or even arcminutes from their centers. The photometric pipelines use them to derive the shape and amplitude of such extended wings, relative to the central peak of a star. The SSC uses pre-existing stellar catalogs to predict the positions of wing and frame stars on the photometric images (magnitude ranges are specified in scParam.par). Once a wing stamp is cut out at the predicted position, its intensity-weighted first moment of pixel values is calculated, and then the stamp is re-cut based on the new position. No recentering is attempted for frame stamps.

The selection of wing stars is controlled by the ws group of input parameters. If a frame has more than one qualifying star, none are selected. The user must set the magnitude limits appropriately to acquire the desired number of stars per run. Stars which are more than ws_pix_offset from the center of a frame are ignored.

The fs group of parameters are used to select frame stars. These stars are even brighter than wing stars, and are intended to help characterize the ghost structure of the PSF. If a frame has more than one qualifying star, none are selected. The user must set the magnitude limits appropriately to acquire the desired (tiny) number of stars per run. Stars which are more than fs_pix_offset from the center of a frame are ignored.

A note on handling photometric image files

The SSC can handle raw, photometric images files in several ways: first, if ignorePhotomData is set to 1, the SSC ignores all photometric images (and Gang files) completely. If ignorePhotomData is set to 0, then the SSC will look for photometric images either on disk or on tape:

• images on disk: if the user sets fieldInputDevice to disk, then the SSC looks in the fieldInputDir directory for images.
• images on tape: if the user sets fieldInputDevice to tape, then the SSC expects to find the images on a tape (e.g. the first processing of DLT tapes at Fermilab). The tape must be mounted in a drive with device name given by tapeDeviceName. The tape must have an ASCII label at its very beginning, with length exactly tapeLabelLength bytes. The SSC will compare the first word in this label with the tapeLabel value, and halt execution if the two do not match. Following the tape label should be individual photometric images, written one after another, field by field, 5 images per field (that is, the re-arranging of image data analogous to Gang - Fang processing has already been done by the DA). The SSC will check to make sure that the keywords

     RUN  FILTER  FRAME  CAMROW  CAMCOL  

  in the FITS header have the values expected for the image.

In addition, if the SSC was reading images from a tape, and you set the keepPhotomImages parameter to 1, then it will place very large raw photometric image files, idR*.fit, into the fieldInputDir directory (they are simply copied from the tape, and not modified in any way).

If the ignorePhotomData parameter is set to 1, then all the photometric data is ignored; this means that no scFrame, scWing, or idR files will be created. Moreover, the output scFang files will contain only the parameters for bright stars measured by the DA system.

Running the Serial Stamp Collecting Pipeline

$SSC_DIR/bin/ssc

  > $SSC_DIR/bin/ssc
    Executing commands in /u/products/astrotools/v1_9/etc/astrotoolsStartup.tcl
    Executing commands in /u/products/dervish/v5_0/etc/dervishStartup.tcl: 
    Executing commands in /u/richmond/.dervish: 
    Executing commands in /peyton/scr/lucifer0/richmond/ssc/etc/sscStartup.tcl: 
  ssc> 

Now, one can either change directories to a directory containing the scPlan.par file, and then run the pipeline:

  ssc> cd /data/dp1.4/sscdata/input
  ssc> run_ssc_pipeline

or, supply the name of the file (including a relative or absolute path) as an argument to the pipeline script:

  ssc> run_ssc_pipeline /data/dp1.4/sscdata/input/scPlan.par

In either case, a large number of messages appear on your screen as the SSC works its way through the data:

  ssc> run_ssc_pipeline
    Entering proc init_discard_bad_photom_stars_2 
    entering init_calc_flats
      .
      . 
      etc.
      .
    Entering clean_up_process
    done with clean_up_process 
    {ELAPSED 33.735} {CPU {{OVERALL 32.190} {UTIME 29.470} {STIME 2.720} {CUTIME 0.000} {CSTIME 0.000}}}
    0
  ssc>

If all goes well, the last thing printed by the SSC will be its return code, 0. If not, some sort of error occurred, and the last few lines of the SSC process describe the problem.

Examining output

If all went well, the SSC should produce two-and-a-half sorts of output.

First, the half-output: if the SSC was reading photometric images from tape, and keepPhotomImages was set to 1, then the directory fieldInputDir will have FITS versions of all the photometric images which were processed. In such cases, this will probably be much larger than the real outputs described below.

The first real type of output will be in the output directory specified in the scPlan.par file; it should contain one or more Fang files. A typical size for a Fang file is 400-700 kB, for a camera column containing photometric chips (camCol 1-6), or about 40 kB, for a camera column with astrometric chips only (camCol 7-11). One can use the standard Dervish tools, such as fits2Schema and chainPage to examine the contents of the Fang file, one HDU at a time.

Sometimes it's nice to look at the postage stamps cut out by SSC, since the eye is so good at picking out cruddy data in a crowd. One can use fits2Schema to read one of the HDUs from a Fang file that contains postage stamps, specifying a data type of SCUSTAMP, like so: assuming that the output directory is $SSCDATA_DIR/output, one can type:

  ssc> cd $SSCDATA_DIR/output
  ssc> set hdr [hdrNew]
    h2
  ssc> set ch [fits2Schema scFang-000581-1-0026.fit SCUSTAMP $hdr -hdu 1]
    h3
  ssc>

  ssc> make_ustamp_mosaic $ch
    h4
  ssc> saoDisplay h4

The output directory will also contain FITS images containing any wing stars or frame stars that were cut out during the run. Each file is a single FITS image, which should be either a sub-frame centered on the star (wing stars), or a complete copy of the raw frame (frame stars). One can use the standard DERVISH commands for reading and displaying images (i.e. REGIONs) to examine each file individually. For example, assuming that one wing star is in file scWing-000505-12-0039.fit.

   ssc> cd /data/dp1.4/sscdata/input
   ssc> set reg [regReadAsFits [regNew] scWing-000505-12-0039.fit]
   h1
   ssc> saoDisplay $reg
   1
   ssc>

Finally, one can examine the diagnostic output file to see how many stars were detected and matched in each field, etc. Since the file has a relatively simple ASCII format, it can be browsed directly. However, it may be more convenient to use the ssc_results procedure to create a 4-panel graph showing the behavior of various diagnostics as a function of field number. This is probably the quickest way to find a big problem.

The SSC pipeline works in a rather straightforward way and its flow chart is in essence a linear list of executed procedures.

 
Initialise Modules
Read Plan/Parameter Files
Read Star Catalog
{if needed: read flat-field vectors}

Foreach field {
    Locate matching astrometric Gang files
    Locate matching photometric Gang files
    Locate photometric images (either on disk or tape)
    Find catalog stars on photometric images 
    Cut out wing and frame stars and write to disk
    Read astrometric keywords from Gang file headers 
    Read quartiles from Gang files
    {if needed: calculate flat-field vectors}
    Find stars appearing in both astrometric Gang files
    Discard stars which are too close to defects
    Find the surviving stars on photometric images 
    Cut out stamps from photometric images 
    Discard stars which are too close to defects
    Measure parameters for the surviving stars
    Mark stars with "bad" parameters
    {if needed: discard stars with "bad" parameters}       
    Write surviving stamps to Fang file
    {if needed: write diagnostics}        
}

Finish wing and frame stars log files

################################################################# 
# This is the Plan file for the Serial Stamp Collecting Pipeline 

#
# Required Generic Plan Fields
action              ssc                   # Plan type
version             v1.0                  # Software version to use
parameters          scParam.par           # Tunable parameters file

#
# Optional Generic Plan Fields
priority            1                     # Execution priority
oid                 "23.45.34.23"         # Database object identifier
targetDate          "1999/04/18"          # Target date (local time zone)
created             "1965/04/18 05:40:00" # Creation time (UT)
authors             "User Abuser"  	  # Authors
comment             "example"             # Comment
diagnostics         1                     # if > 0, do create a file with
                                          # diagnostic output from each field
diagFile            scDiag                # prefix of the file into which 
                                          # diagnostic output will be placed.
                                          # Name will include run and camCol. 
#                                       
# filters order
ccdrow_r            1
ccdrow_i            2
ccdrow_u            3
ccdrow_z            4
ccdrow_g            5
ccdrow_o            6
ccdrow_l            7
ccdrow_t            8
ccdrow_s            9

#################################################################
# List of paths to various required files

# the param file given above as 'parameters' may be found here
parametersDir 	    $SSCDATA_DIR/input

# directory with the CCD parameters file ...
configDir           $SSCDATA_DIR/input
# ... and file names
ccdConfig           opConfig-51259.par    # amplif. config
ccdBC      	    opBC-51259.par	  # bad column file
ccdECalib 	    opECalib-51259.par	  # readnoise/gain file 
ccdCamera           opCamera-51259.par    # camera layout

# directory with astrometric gangs 
aGangInputDir       $SSCDATA_DIR//Gangs               

# directory with photometric gangs  
pGangInputDir       $SSCDATA_DIR//Gangs       

# directory with photometric images  
fieldInputDir      $SSCDATA_DIR//idR               

# info about input device
fieldInputDevice    disk                  # disk or tape
tapeDeviceName      /dev/nrmt3h           # name of tape drive
tapeLabel           VOL1JG0001            # if "tape", name of volume label
tapeLabelLength     80                    # if "tape", length of tape label 
tapeSkipFiles       50                    # skip this many images at the 
                                          # very start of the tape (does not 
                                          # include the tape label)
tapeLogFile         idTapeLog-JG0001.par  # if "tape", name of idTapeLog file

# Directory with catalog of known objects
koDir               $SSCDATA_DIR//input 
koVersion           v1_0                # Version of known object catalog to use. 
koFileBase          koCat               # prefix of the catalog file  
wingFile            scWing              # prefix for the file with the list of
                                        # "wing stars". Name includes run and 
                                        # camcol. Ex: scWing-000581-1.par
frameFile           scFrame             # prefix for the file with the list of
                                        # "frame stars". Name includes run and 
                                        # camcol. Ex: scWing-000581-1.par 

# all the rest of the input comes from here
inputDir         $SSCDATA_DIR//input     

# put the output here:
outputDir 	    $SSCDATA_DIR/output
 
#################################################################
# Processing Parameters

# which data to process
run                 581                 # Imaging run number. 
camCol   	      1		        # Camera column
startField           10                 # start pipeline with this field
                                        # Gang files must start with 
                                        # a number <= startField - 3 
endField             66                 # stop with this (inclusive)
                                        # Gang files must finish with 
                                        # a number >= endField + 10

# what to do with the data
keepPhotomImages      1                 # if 1, keep photometric images on disk
                                        # if 0, delete them after use
                                        # this is probably 1 if using "disk"
                                        # but possibly 0 if using "tape"
writePhotomOnly       0                 # if 1, read photometric images off
                                        # tape, write to disk, do nothing else
ignorePhotomData      0                 # if 1, ignore any photometric data,
                                        # working only on astrometric data
  
# aux stuff
verbose               1                 # verbose > 0 means print a lot
display		      0                 # display on/off; shows various images  
                                        # as the pipeline progresses, waiting 
                                        # for user input after displaying each one

#
# Software parameters for SSC
#

# matching stars
am_xpos_field        rowCentroid   # name of field (from SCPARAMBS structure) used 
                                   # to compare astrometric stars in one direction
am_ypos_field        colCentroid   # name of field (from SCPARAMBS structure) used 
                                   # to compare astrometric stars in other direction
am_match_diff           8          # two astrometric stars with centers which are
                                   # this close (or closer), in pixels in each 
                                   # direction (not in true geometric distance)
                                   # are considered a match

# defining flat-fielding method
ff_none                 0          # perform no bias-subtraction or flatfielding
ff_quartiles            1          # use a flatfield vector based on the quartiles                                  
ff_fixed                0          # use a fixed flatfield vector in a disk file
ff_filename         scFlat_        # base of the filename inside which the flatfield 
                                   # vector for each chip lives (as a FITS image).
                                   # Ex:  scFlat_42.fit, 42=camera row and column
ff_maxncol             2128        # max number of cols in any photometric chip  
 
# discarding bad data
bc_distance              10        # if a star is this close (pixels) to 
                                   # a known chip defect, ignore it

# calculating sky
sk_edge_npix             10        # use pixels within this many of edge
                                   # of a postage stamp to calc sky
sk_clip_nsigma          3.0        # clip values this many sigma from mean
                                   # when calculating sky value in stamp
sk_clip_niter             2        # make this many iterations in clipping
                                   # when calculating sky value in stamp
st_recenter_boxsize      11        # if > 0, calc center of a star using
                                   # first moments inside a box with this 
                                   # half-length at center of stamp, and 
                                   # re-cut stamp at the new position.
                                   # if == 0, do not re-cut stamp; keep stamp 
                                   # based on position in the astrometric chips
st_conv_sigma           1.2        # width (pix) of gaussian with which to 
                                   # convolve stamp before measuring its properties

# discarding instructions
ds_statusfit_delete       0        # if 1, discard stars which have "statusfit" 
                                   # field != 0
ds_filterlist           r g        # test stars only in these filters for valid 
                                   # parameters
ds_minrmajor            0.9        # rMajor must be > this to be OK
ds_maxrmajor            1.6        # rMajor must be < this to be OK
ds_minrminor            0.9        # rMinor must be > this to be OK
ds_maxrminor            1.6        # rMinor must be < this to be OK
ds_minpeak            100.0        # peak must be > this
ds_maxpeak          10000.0        # peak must be < this
ds_radius_bit             1        # set this bit in the "sscstatus"
                                   # field of SCPARAMBS if any radius
                                   # length is outside allowed range
ds_radius_delete          0        # if 1, discard stars which fail radius tests
ds_peak_bit               2        # set this bit in the "sscstatus" field of SCPARAMBS 
                                   # if peak is outside allowed range
ds_peak_delete            0        # if 1, discard stars which fail peak tests

# "wing" stars parameters
ws_pix_offset           400        # max number of pixels away from center
                                   # of its CCD chip for a "wing star"
ws_min_mag              8.0        # minimum mag allowed for "wing star"
                                   # (in whatever passband is in catalog)
ws_max_mag             14.0        # maximum mag allowed for "wing star"
ws_box_size             200        # size of box, in pixels, which we cut

# "frame" stars parameters
fs_pix_offset           300        # max number of pixels away from center
                                   # of its CCD chip for a "frame star"
fs_min_mag              1.0        # minimum mag allowed for "frame star"
                                   # (in whatever passband is in catalog)
fs_max_mag              8.0        # maximum mag allowed for "frame star"
                                      

Please send any comments or suggestions to Zeljko Ivezic