NAME

imdetect - Determine rough positions of sources in the whole field.

USAGE

imdetect infile outfile subcells xcellsize ycellsize fieldbkdens

DESCRIPTION

IMDETECT determines rough positions of candidate sources in the whole field. The field is scanned with a sliding bin of a detect cell and a source detection is defined to occur whenever the threshold is exceeded. Subsequent processing involves association of adjacent or contiguous cells, and identifying the position and minimum radius of the source or sources in each region.

The task was converted from ROSAT level zero processing system(SASS) and tested for ROSAT/HRI and ASC(AXAF Science Center)/HRC.

Currently, the snr threshold is either calculated from the parameter "fieldbkdens" and three snr coefficients, or it comes directly from the parameter "snr_thresh_min", whichever is larger.

NOTE: Unlike ldetect in xspatial, imdetect can operate on image files as well as qpoe files.

PARAMETERS

infile = "" prompt = input qpoe or image file

Required input filename. It can be a qpoe file or an image file.

outfile = "" prompt = output (ruf) position table file

Required output filename. The file is written in a table format. The name may be specified by supplying the rootname and "_ruf.tab" extension will be appended. For example input "test" becomes "test_ruf.tab". The column names and definitions are as follows:

    blob #  - number of the current contiguous region (or "blob" )
    peak #  - number of this detection found within a blob
              (eg. if value n, it means this is the n_th peak found
		   within the blob)
    x       - x source position in pixels
    y       - y source position in pixels
    dx      - x detector coords. in pixels (= column_x - 1.0)
    dy      - y detector coords. in pixels (= 4096.0 - column_y)
    res?    - a flag indicating whether a source is big enough to 
              contain more than 1 source.  (yes=1, no=0)
    min r   - minimum radius of a source in pixels
    cellx   - x detect cell size in pixels 
    celly   - y detect cell size in pixels 

subcells = prompt=number of subcells per detect cell in a dimension

number of subcells per detect cell in each dimension.

(e.g.  If subcells=3, there will be 3*3=9 subcells per detect cell.)
NB: This parameter determines the step size.

xcellsize = prompt = x detect cell size in pixels

x detect cell size in pixels. Recommend using 24 pixels for ROSAT/HRI and 8 pixels for ASC data.

ycellsize = prompt = y detect cell size in pixels

y detect cell size in pixels. Recommend using 24 pixels for ROSAT/HRI and 8 pixels for ASC data.

fieldbkdens = 0.prompt = field background density in cts/arcmin**2

field background density in cts/arcmin**2

max_src_num = prompt = max number of sources

maximum number of sources to be detected. If max sources found, the process will be stopped and write the sources to the ruf table.

(pixelsize = 0.5) [real]

arcseconds per pixel

(snrfactor = 1.) [real]

reducing factor for snr threshold

(blobsize = 1024) [int]

maximum blob size in pixels for y-dimension. There is no blob size limit for x-dimension.

(boxxmax = 3) [int]

max x box dimensions in subcells. (see "boxymax" below)

(boxymax = 3) [int]

max y box dimensions in subcells. If the size of the box around a blob is larger than boxxmax and boxymax, then the box will be labelled big and is thought to possibly contain more than one source.

(ctwtfactor = 3) [int]

A flag indicates how the count weight factor (CWF) was calculated.

    ctwtfactor   CWF
    ----------   ----------
       1         src_counts - bkg_counts
       2         [(scr_counts - bkg_counts) / src_counts ] ** 2
       3            1

    [ Currently, no background map is used and bkg_counts is zero. ]

(display = 1) [int]

display level (>=1 for display)

(clobber = no) [boolean]

overwrite existing file?

(maxblobs = 100) [int]

max number of blobs allowed per field

(numcellsizes = 1) [int]

number of different detect cell sizes to run

(num_16_snr_coeffs = 3) [int]

number of snr coefficients for detect cell area (16 arcsec**2)

(snr_16_1_coeffs = 1.5336) [real]

first snr coefficient for detect cell area (16 arcsec**2)

(snr_16_2_coeffs = 0.22547) [real]

second snr coefficient for detect cell area (16 arcsec**2)

(snr_16_3_coeffs = 0.0138237) [real]

third snr coefficient for detect cell area (16 arcsec**2)

(snr_16_thresh_min = 2.5) [real]

minimum snr value for detect cell area (16 arcsec**2)

(num_64_snr_coeffs = 3) [int]

number of snr coefficients for detect cell area (64 arcsec**2)

(snr_64_1_coeffs = 1.5336) [real]

first snr coefficient for detect cell area (64 arcsec**2)

(snr_64_2_coeffs = 0.22547) [real]

second snr coefficient for detect cell area (64 arcsec**2)

(snr_64_3_coeffs = 0.0138237) [real]

third snr coefficient for detect cell area (64 arcsec**2)

(snr_64_thresh_min = 2.5) [real]

minimum snr value for detect cell area (64 arcsec**2)

(num_144_snr_coeffs = 3) [int]

number of snr coefficients for detect cell area (144 arcsec**2)

(snr_144_1_coeffs = 1.5336) [real]

first snr coefficient for detect cell area (144 arcsec**2)

(snr_144_2_coeffs = 0.22547) [real]

second snr coefficient for detect cell area (144 arcsec**2)

(snr_144_3_coeffs = 0.0138237) [real]

third snr coefficient for detect cell area (144 arcsec**2)

(snr_144_thresh_min = 2.5) [real]

minimum snr value for detect cell area (144 arcsec**2)

(num_576_snr_coeffs = 3) [int]

number of snr coefficients for detect cell area (576 arcsec**2)

(snr_576_1_coeffs = 1.6952) [real]

first snr coefficient for detect cell area (576 arcsec**2)

(snr_576_2_coeffs = 0.30085) [real]

second snr coefficient for detect cell area (576 arcsec**2)

(snr_576_3_coeffs = -0.0011031) [real]

third snr coefficient for detect cell area (576 arcsec**2)

(snr_576_thresh_min = 2.5) [real]

minimum snr value for detect cell area (576 arcsec**2)

(prf_sigma = 0.5) [real]

prf sigma in arcseconds. Currently, this is used as a flag indicating where to get the snr coefficients. If it is greater than zero, then coefficients will be read from user's par. Otherwise, they will be retrieved from prf_table.

Recommend setting prf_sigma greater than zero for ASC data to skip prf_table. [ see prf_table ]

(energy = 0.) [real]

energy in KeV. Energy will be used when getting the snr coefficients from prf_table. [ see prf_sigma]

(prf_table = "xspatialdata$prfcoeffs.tab") [string]

Prf coefficient table. Entries for ROSAT PSPC/HRI & Einstein IPC/HRI. Lookup based on value of energy. Returns coefficients assiciated with a default lookup when energy=0.0; returns coefficients closest to the energy when exact match is not found.

Currently, entries for AXAF/ACIS and AXAF/HRC are only temporary. [ see prf_sigma ]

EXAMPLES

1. run imdetect with ROSAT/HRI qpoe file :

        de> flpr
	de> unlearn imdetect
	de> imdetect clob+
        input qpoe or image file: xdata$rh110267n00.qp
        output (ruf) position table file:   test
        detect cell size smooth factor (1): 3
        x detect cell size in pixels (24): 
        y detect cell size in pixels (24): 
        field background density in cts/arcmin**2 (0.001): 

         -- created output table: test_ruf.tab --

        de> flpr
	de> unlearn imdetect
        de> imdetect snr_16_thres=3.6  clob+
        input qpoe or image file: xspatialdata$asc_hrc.imh
        output (ruf) position table file: hrc
        detect cell size smooth factor (1): 
        x detect cell size in pixels (24): 8
        y detect cell size in pixels (24): 8
        field background density in cts/arcmin**2 (0.001): 

         -- created output table: hrc_ruf.tab --

SEE ALSO

Documentation on the detect algorithms and philosophy along with limitations in (help explain_detect ).