; STRAN ;----------------------------------------------------------------------- ;! Task compares ST tables, find image coordinates (e.g. guide star ) ;# TASK IMAGE UTILITY OPTICAL ;----------------------------------------------------------------------- ;; Copyright (C) 1995-1996, 2009 ;; Associated Universities, Inc. Washington DC, USA. ;; ;; This program is free software; you can redistribute it and/or ;; modify it under the terms of the GNU General Public License as ;; published by the Free Software Foundation; either version 2 of ;; the License, or (at your option) any later version. ;; ;; This program is distributed in the hope that it will be useful, ;; but WITHOUT ANY WARRANTY; without even the implied warranty of ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the ;; GNU General Public License for more details. ;; ;; You should have received a copy of the GNU General Public ;; License along with this program; if not, write to the Free ;; Software Foundation, Inc., 675 Massachusetts Ave, Cambridge, ;; MA 02139, USA. ;; ;; Correspondence concerning AIPS should be addressed as follows: ;; Internet email: aipsmail@nrao.edu. ;; Postal address: AIPS Project Office ;; National Radio Astronomy Observatory ;; 520 Edgemont Road ;; Charlottesville, VA 22903-2475 USA ;----------------------------------------------------------------------- STRAN LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC STRAN: Task compares ST tables and finds image Coordiantes. INNAME Image name(name). INCLASS Image name(class). INSEQ 0.0 9999.0 Image name(seq. #). 0=>high INDISK Disk drive #. 0=>any INVER ST Table of Star Pixels IN2VERS 0.0 46655.0 ST Table of Star Coordinates BPARM 1: >0 update image header 2: Max number of triangles 3: Print Level (0 to 2) 4: >0 not use header as fit CPARM 1: Min triangle size (pixels) 2: Max triangle size (pixels) 3: Min triangle size (arcsec) 4: Max triangle size (arcsec) 5: Star match distance (pix) 6: Min Number Stars in fit 7: Max Triangle match delta 8: Min Triangle side ratio DPARM 1: Estimated X Pixel scale 2: Scale error (arcs/pix) 3: Estimated X Pixel scale 4: Scale error (arcs/pix) 5: Orientation Angle 6: Angle error (degrees) 7: Image Center Ra 8: Ra error (degrees) 9: Image Center Dec 10: Dec error (degrees) ---------------------------------------------------------------- STRAN Type: Task Use: STRAN reads in two ST tables and determines the image scale and orientation. The first ST table must contain the pixel locations of stars in the image (See STFND). The second ST table must contain coordinates (RA+DEC) of stars in the image (Use, for instance, GSCAT and GSTAR to read the NASA Guide Star cataloge to get a list of star coordinates). Since the two ST tables will have the Stars in different orders, STRAN will search for matching triangles of sources. Once matches are found, a best match to the star coordinates will be attempted. NOTE!!! STRAN WILL ONLY WORK IF THE STAR TABLES HAVE ROUGHLY 30% OVERLAP! (IF ONLY 10 STARS IN 1 TABLE ARE ACTUALLY AMOUNG 1000 STARS IN THE SECOND TABLE, STRAN WILL PROBABLY _NOT_ FIND A SOLUTION.) IT IS CERTAINLY BEST TO FIRST ESTIMATE THE IMAGE COORDS AND PLOT THE STAR LOCATIONS FIRST TO COMPARE LISTS. STRAN BECOMES EXTREAMLY SLOW WITH MORE THAN 300 STARS PER ST TABLE. THIS IS AN EXTREAMLY EXPERIMENTAL PROGRAM!!!!!!!!!!!!!!!! Adverbs: INNAME......Image name (name). Standard defaults. INCLASS.....Image name (class). Standard defaults. INSEQ.......Image name (seq. #). 0 => highest. INDISK......Disk unit #. 0 => any. OUTVERS.....Version number of ST (star position) file to be created. 0 => highest+1. INFILE......Name of file containing star positions; name should be of the form: myarea:filename.ext ---------------------------------------------------------------- STRAN: Task to read two ST (star position) tables and find the image orientation RELATED PROGRAMS: CNTR, PCNTR, GREYS, PROFL, STARS, STFND, GSTAR GSCAT, TABED, PRTAB DOCUMENTOR: Glen Langston PURPOSE STRAN - Attempts an "automatic" determinate of the location, pixel scale, and orientation of an image. Typical use will be to determine the orientation of an optical image so that it can be overlayed with a radio image. Finding the image para- meters is done by providing STRAN with two ST tables, one containing the list of PIXEL locations of stars in the image and the second containing the list of COORDINATE locations of stars in the image. There must be at least 30 % overlap in the star lists. (ie 30 % of the stars in one list must be present in the other list, and visa-versa.) STRAN WILL NOT WORK IF THERE IS NOT SUFFICIENT OVERLAP IN THE ST TABLES. STRAN WILL WORK MUCH BETTER IF THE TWO LISTS CORRESPOND TO THE SAME STARS! Use of STRAN requires serveral steps, listed below: 1. Determine the image properties as well as posible. Fill the image header with the best estimates of the location of a reference pixel, pixel size and image orientation using the AIPS verb PUTHEAD. The critical KEYWORDS are listed below: CRVAL1 X-Location (ie RA in degrees) of the reference pixel CRVAL2 Y-Location (ie DEC in degrees) CRPIX1 X-Location of reference Pixel (origin of pixel coordinate system CRPIX2 Y-Location of reference Pixel CDELT1 X-Size of a Pixel (in degrees) CDELT2 Y-Size of a Pixel (in degrees) CROTA1 Orientation angle of image (in degrees) CROTA2 Orientation angle of image (usually = CROTA1) 2. Find the Guide Star Table containing the region of interest. There are Millions of stars in the NASA guide star catalog so every few 10s of square arc minute region will contain some Guide Stars. Use the Task GSCAT to read the NASA provided REGIONS.TBL containing the Guide Star table number corresponding to each region of the sky. 3. Transfer the Guide Star table of interest to the AIPS area called FITS (renaming the file to upper case letters). Use IMLOD to read in the Guide Star Table which will be called an UK (unknown) AIPS table. 4. Use the Task GSTAR to convert the UK table of coordiantes into an AIPS ST table. 5. Use the Task TABED to remove all stars outside the region of interest. If many stars remain (more than 100) use TABED to remove all but the brightest stars. Below is a PRTAB listing of the table created by GSTAR RING-PSS-O .MWFLT . 1 Disk= 3 ST Table version 4 Title: AIPS ST star positions table Created by GSTAR on 30-JUN-1992 11:04:29 Last written by GSTAR on 02-JUL-1992 00:17:35 Ncol 7 Nrow 2080 Sort cols: Table has 1 keyword-value pairs: TABEPOCH = b1950.0 COL.NO 1 2 3 4 5 6 7 ROW RA---ARC DEC--ARC DELTRA-- DELTDEC- POSANG STAR LABEL NUMB DEGREES DEGREES DEGREES DEGREES DEGREES INDEX STR 1 2.52512D+2 1.49264D+1 1.674E-3 1.674E-3 1.281E-2 0.0 S1 2 2.52512D+2 1.49264D+1 1.563E-3 1.563E-3 1.314E-2 0.0 S1 3 2.53565D+2 1.48021D+1 2.681E-3 2.681E-3 1.056E-2 0.0 S2 4 2.53565D+2 1.48020D+1 2.958E-3 2.958E-3 1.009E-2 0.0 S2 5 2.52367D+2 1.50045D+1 1.009E-3 1.009E-3 1.523E-2 0.0 S3 6 2.53312D+2 1.49709D+1 9.801E-4 9.801E-4 1.537E-2 0.0 S4 7 2.53399D+2 1.48005D+1 1.121E-3 1.121E-3 1.473E-2 0.0 S5 ... Note that the Epoch of the coordinates of the stars is recorded with the keyword TABEPOCH, in this case 1950 coords. Note that the ST table contains several entries for the same star, which come from different measurements of the star brightness. The RA and DEC are in degrees, and the size of the star (columns 3 and 4) are the size of the star on the Palomar sky survey. The original magnitude of the star is recorded in the Position angle column, but scaled down by 1000. (ie star S5 in row 7 is a 14.7 magnitude star.) Make a plot the stars on the image, look for matches. 6. Take the input image and convert it with MWFLT (if necessary) Usually scanners produce values from 0 to 255, but if it is desired that the empty sky have values near 0, use MWFLT to median window subtract the sky. 7. Use the task STFND to find bright stars in the image. First make ST tables with the star coordiantes, so that CNTR can be used to mark identified Stars. When the identifications seem good, make an ST table with Pixel Coordinates. 8. Finally, run STRAN to identify stars in the two lists and determine the image transformation. COMMENTS You can view the contents of the ST file with PRTAB. The Palomar Sky Survey (PSS) scanned with a page scanner is expected to be a common input in to STRAN. A few notes about the PSS: The PSS has a angular scale of 67.3 arc seconds per millimeter. Since Common scanners use dots per inch scales, this is converted to arc-seconds per pixel below: DOTS PER INCH ARC-SECONDS PER PIXEL ------------- --------------------- 800 2.14 600 2.85 400 4.27 300 5.7 200 8.5 100 17.1 75 22.8 50 34.2 The Palomar Sky Survey was done in two colors E (Red) and O (Blue). ----------------------------------------------------------------