Program: points Purpose: Automatic point source extractor. Uses a histogram method to determine the zerolevel and the noise in a map. Category: ANALYSIS File: points.src Author: Fred Lahuis Keywords: INSET= Input set. The subsets of the input have to be two dimensional. OUTSET= The output set will have a parameter [none] axis added, called PARAM_POINT. If such an axis already exists in the input set, an index number will be attached to it. If the output set already exists it will be assumed to have a dimension of at least three and the third axis will be assumed to be the parameter axis. The parameter axis runs from 0 to 3. 0 --> original image 1 --> background subtracted image 2 --> background 3 --> noise (**)OVERWRITE= Asked if the output set already exists. y/[n] If no is entered OUTSET= will be asked again. If yes is entered the output set is assumed to be of the proper dimensions (including the parameter axis). if this is not the case the program may crash. MASKSET= Set used to indicate the points to be [none] or not to be used in the determination of the background and the noise. The points not to be used have the value blank. The subsets have to be two dimensional. If the number of subsets equals the number of subsets of the input set, each subset will be assumed to contain a mask for the corresponding subset of the input set. Otherwise the subset at the highest level is used as a mask for all the input subsets. BOX= Area in subset(s) to work on [whole set] OBJFILE= Base name of output file [none] .objs In the file .objs information on the found pointsources is given. All subsets are written to this file and only the last iteration is saved. HISTFILE= Base name of output file [none] .hist In .hist the results of the histogram determination of zero and noise for all areas are given. All subsets are written to this file and only the last iteration is saved. RCLFILE= Filename for recall file [none] The file will get the extension .rcl and can be used as input for e.g. CPLOT. The files will (if necessary) get an extension for the subset number. The recall files are rewritten after each iteration, so only the result for the last iteration is saved. SIDE= Square size of the subareas [100] SEP= Separation between subarea centers [50] The resolution in the resulting background and noise images is directly dependent on this parameter. To obtain a maximum resolution SEP=1 should be used. AREA= Size of the area around a pixel. [10] If a pixel is the local maximum in this area the intensity weighted mean is used as the position for the 'point'source. There may not be any blanks in the area. EDGE= Minimum distance from the side of the map [area/2] SN= Minimum signal to noise for point source [3.0] The value for the point sources must be larger than the 'calculated' ZERO + SN * NOISE **NOISE= If this keyword is specified, this value is used in the selection of pointsources instead of the calculated value of the noise. **NPOINTS= Minimum number of points [20 percent of subarea] required to accept the histogram result. Description: This program creates a background image and a noise image of the input image. From this it extracts point sources. It divides the map into sub areas of (side) by (side) pixels. The area centers are separated by (sep) pixels. So every pixels is within (side/sep)^2 areas. This means that maximum coverage, and so maximum resolution in the background and noise image, is obtained when sep=1. In each area the program determines the zerolevel and noise in a two step histogram method. In the first step a rough estimate of the zerolevel is made. This is used to limit the number of points in the determination of the zero and noise. In the second step only the points left of the maximium are used to avoid confusion by extended sources or a large number of smaller sources. The zerolevel is taken as being the maximum point in the distribution. The noise at the half maximum point. The background and noise maps are determined by taking the plain average of all coverages. From background and noise maps the 'pointsources' are extracted as being those points that have a value higher than the zerolevel plus (sigma) times the noise and have the highest value in an (area) by (area) pixel area. In the outfile the following values are written for each pointsource: xpos, ypos, st.dev. x, st.dev. y, background, noise, peak level, SN The peak level is the data value minus the background value. SN is the peak level divided by he noise. The positions as listed in the .objs and .rcl files are intensity weighted averages in an (area) by (area) pixel area. In the .objs file also the standard deviations are listed. Comments: All keywords, except for INSET and FILENAME are repeated keywords. This makes interactive use of the program possible. Examples: Example of an .objs file. In this file the first line contains the parameters used. # side = 75 sep = 25 subbox = 10 sn = 3.0 3.0 edge = 10 # set=test subset 0, box [-127,128,-127,128] # ra dec sd_ra sd_dec zero noise peak intens SN 2h 17m 53.8s 61d 26m 31.5s 0.010 0.012 6.675 1.261 15.601 8.925 7.08 2h 18m 9.6s 61d 28m 34.9s 0.008 0.007 6.898 1.071 113.824 106.926 99.87 2h 18m 9.9s 61d 39m 15.9s 0.012 0.012 6.908 0.958 12.220 5.313 5.54 2h 18m 33.2s 62d 14m 39.7s 0.011 0.011 0.970 1.087 8.233 7.263 6.68 2h 18m 56.9s 61d 36m 38.7s 0.011 0.011 6.838 1.039 31.965 25.127 24.18 2h 20m 53.4s 62d 11m 45.8s 0.011 0.011 0.450 1.027 7.746 7.296 7.10 2h 21m 32.4s 61d 47m 31.2s 0.011 0.011 9.753 4.967 260.092 250.340 50.40 2h 21m 38.1s 61d 50m 16.3s 0.011 0.011 9.753 4.967 222.079 212.327 42.75 2h 21m 50.8s 61d 53m 4.2s 0.011 0.011 7.522 4.333 575.238 567.716 131.04 2h 22m 12.5s 62d 6m 22.1s 0.009 0.009 4.361 2.299 71.737 67.377 29.31 Example of a .hist file Listed here is the pixel position of the lower left corner of the subarea, the number of pixels in that area, the zerolevel and noise for that area. When the histogram method is not succesful a - - is written where the zero and noise should be. # set=test subset 0, box [-119,120,-119,120] # side=100 sep=50 0 0 900 +0.0084 0.0548 50 0 5900 -0.0577 0.0746 100 0 5126 -0.0330 0.0867 150 0 126 -0.0089 0.1341 200 0 0 - - 0 50 900 +0.0195 0.0772 50 50 5900 -0.0245 0.0930 100 50 5170 -0.0106 0.1087 150 50 170 +0.0336 0.1690 200 50 0 - - 0 100 900 -0.0234 0.0892 50 100 5900 -0.0480 0.1728 100 100 5196 -0.0300 0.1252 150 100 196 +0.0855 0.1188 200 100 0 - - 0 150 801 -0.1109 0.1069 50 150 5251 -0.1427 0.1487 100 150 4628 -0.1624 0.1396 150 150 178 -0.1508 0.0938 200 150 0 - - 0 200 351 -0.1630 0.0536 50 200 2301 -0.1949 0.0996 100 200 2028 -0.1935 0.0977 150 200 78 -0.3101 0.0976 200 200 0 - - Example of a recall file: *1950.0 2 17 53.8 *1950.0 61 26 31.5 *1950.0 2 18 9.6 *1950.0 61 28 34.9 *1950.0 2 18 9.9 *1950.0 61 39 15.9 *1950.0 2 18 33.2 *1950.0 62 14 39.7 *1950.0 2 18 56.9 *1950.0 61 36 38.7 *1950.0 2 20 53.4 *1950.0 62 11 45.8 *1950.0 2 21 32.4 *1950.0 61 47 31.2 *1950.0 2 21 38.1 *1950.0 61 50 16.3 *1950.0 2 21 50.8 *1950.0 61 53 4.2 *1950.0 2 22 12.5 *1950.0 62 6 22.1 Updates: ROBAS Original Program. June 1993: FL Program adapted to Gipsy. Document created. August 1993: FL Background and noise maps added. Sep 15 1993: FL First Gipsy version installed. Feb 22 1993: FL Default SN changed and Bug removed. June 1994: FL Histogram method simplified. Sept 7 1994: FL New version installed