| using_detect | xray.xspatial.detect | using_detect |
detect -- package of source detect tasks
This document describes the tasks available in the detect package.
This writeup is intended to introduce User's to the set of prototype Detect tasks installed in PROS and show the path in which tasks are run. The Detect we have written is a local detect. A series of 5 tasks, Cellmap, Snrmap, Lpeaks, Bkden, and Bepos will prepare and scan your data for sources and write the detected positions to a table file. Imcontour/Tvimcontour can read the table and display the sources. A utility task detmkreg will make a region file of sources that can be 'read' in SAOIMAGE. A new task, lmatchsrc has also been added to the detect package. Lmatchsrc consolidates detections from one or more runs of ldetect into unique sources in a field. Documentation is available for each task by typing help <taskname>. A detailed document is available by typing 'help explain_detect' that discusses the algorithms, suggestions for choosing parameters, pointers in interpreting results, and limitations of the detect package. ------------------------------------------------------------------------- To Run Local Detect: -------------------- LDETECT runs the detect tasks (CELLMAP, SNRMAP, LPEAKS, BKDEN, and BEPOS) for a single detect cell size and threshold. Intermediate files are saved. ------------------------------------------------------------------------- de> ldetect qpoe file : xdata$rh110267.qp Output table root: harlac24 ROSAT HRI Cellsize in arcsecs - 6|9|12|24|36|48: 24 ... Running Cellmap ... xdata$rh110267.qp[bl=16] -> harlac24.imh add harlac24.imh,cellsize = 24 harlac24.imh updated xdata$rh110267.qp ... Running Snrmap ... Convolving 3x3 cells Convolving 5x5 cells Calculating Snrmap with equation: snrmap=(1.7777*cell3-frame)/((1.7777**2*cell3+oframe)**0.5) Writing Snrmap Image: harlac24_snr.imh ... Running Lpeaks ... src# logx logy physx physy cellx/y snr --------------------------------------------------------- 1 149.00 177.00 2384.00 2832.00 24 24 5.954 2 146.00 276.00 2336.00 4416.00 24 24 30.197 Writing to Output file: harlac24_ruf.tab ... Running Bkden ... Bkden region is circle 256.00 256.00 7.50' Bkden = 12.8558464 counts/arcmin**2 ... Running Bepos ... *** PI bands must be Respecified with input QPOE *** Input Qpoe: xdata$rh110267.qp bkden = 12.8558464 (cts/sq arc-min), 0.0008928 (cts/sq pixel) 2 Rough Position(s) Input src# ra dec physx physy cellcnts framecnts snr --------------------------------------------------------------------------- 1 22:08:38.4 45:31:24.2 2380.1 2829.1 95 67 5.3 2 22:08:41.4 45:44:33.4 2323.5 4407.7 1506 394 31.8 Writing 2 Sources to Output file: harlac24_pos.tab ------------------------------------------------------------------------- To Run Individual Tasks: ------------------------------------------------------------------------- Step 1: ------- CELLMAP copies a qpoe file and creates an image with a specified cell size. Each image pixel represent 1/3 of the detect cell in size. If, after blocking the image size is > 512x512 pixels the image is subsectioned and the center 512x512 image is written out. Depending on the Mission and Instrument (ROSAT HRI|PSPC, Einstein HRI|IPC) of the input qpoe the User is prompted with detect cell size choices in which we have computed the prf constants alpha and beta. (alpha is the integral of the psf over the detect cell, & beta is the integral of the psf over the detect cell + background cell). ------------------------------------------------------------------------- de> cellmap Input xray Qpoe: xdata$rh110267.qp Output xray image : harlac24 ROSAT HRI Cellsize in arcsecs - 6|9|12|24|36|48: 24 xdata$rh110267.qp[bl=16] -> harlac24.imh add harlac24.imh,cellsize = 24 harlac24.imh updated xdata$rh110267.qp de> ------------------------------------------------------------------------- Step 2: ------- SNRMAP generates an image of net counts signal-to-noise at detect sub-cell resolution from an input image of raw counts at the same resolution (the output of cellmap). ------------------------------------------------------------------------- de> snrmap Input xray image : harlac24.imh Output snrmap image [root_snr.imh]: harlac24 Convolving 3x3 cells Convolving 5x5 cells Calculating Snrmap with equation: snrmap=(1.7777*cell3-frame)/((1.7777**2*cell3+oframe)**0.5) Writing Snrmap Image: harlac24_snr.imh de> ------------------------------------------------------------------------- Step 3: ------- LPEAKS finds local peaks in an image (the output from snrmap) above threshold. In the event of adjacent, or equal values above threshold, lpeaks chooses the first value it encounters. lpeaks was adapted from LVS's peakdet program. ------------------------------------------------------------------------- de> lpeaks Input Snrmap Image: harlac24_snr.imh Output Rough Positions Table: harlac24 src# logx logy physx physy cellx/y snr --------------------------------------------------------- 1 149.00 177.00 2384.00 2832.00 24 24 5.954 2 146.00 276.00 2336.00 4416.00 24 24 30.197 Writing to Output file: harlac24_ruf.tab de> ------------------------------------------------------------------------- Step 4: ------- BKDEN calculates the average background of an image blocked at detect sub-cell resolution (output of cellmap). A simple average of the values in all detect cells in the region of interest is calculated and cells greater than a threshold are rejected. This step is repeated for all unrejected cells untils either no further cells are rejected or a maximum number of iterations has been reached. The final average background is in counts/arcmin**2. The value is written to the bepos parameter bepos.bkden. A default region is used if one is not specified by the user. ------------------------------------------------------------------------- de> bkden Input Image: harlac24.imh Region Descriptor (default): Bkden region is circle 256.00 256.00 7.50' Bkden = 12.8558464 counts/arcmin**2 de> ------------------------------------------------------------------------- Step 5: ------- BEPOS reads the rough positions table (output by lpeaks). The data at the rough position is resampled at full resolution, and if the snr of the source meets the snr_thresh (default is 2.75) a source position is written to the output file, else it is rejected. The algorithm uses the liklihood ratio parameter technique (cf. preprint by w. cash, and memos by s. murray, ssm-102-78 and ssm-103-78). The method was used for the Einstein IPC and given in detail in SAO Special Report 393 by Harnden, Fabricant, Harris, and Schwarz. It is also implemented in the ROSAT HRI level 1 system. ------------------------------------------------------------------------- xp> bepos *** PI bands must be Respecified with input QPOE *** Input qpoe file: xdata$rh110267.qp Field background density in cts/arcmin**2 (12.855846405029): Input rough pos table: harlac24_ruf.tab Output bepos table file: . Input Qpoe: xdata$rh110267.qp bkden = 12.8558464 (cts/sq arc-min), 0.0008928 (cts/sq pixel) 2 Rough Position(s) Input src# ra dec physx physy cellcnts framecnts snr --------------------------------------------------------------------------- 1 22:08:38.4 45:31:24.2 2380.1 2829.1 95 67 5.3 2 22:08:41.4 45:44:33.4 2323.5 4407.7 1506 394 31.8 Writing 2 Sources to Output file: ./harlac24_pos.tab -------------------------------------------------------------------------
