From hoernes@sun25.mpifr-bonn.mpg.de Tue Feb 28 23:00:16 1995 X-VM-Summary-Format: "%n %*%a %-17.17F %-3.3m %2d %4l/%-5c %I\"%s\"\n" X-VM-Labels: nil X-VM-VHeader: ("Resent-" "From:" "Sender:" "To:" "Apparently-To:" "Cc:" "Subject:" "Date:") nil X-VM-Bookmark: 1 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["2312" "Tue" "28" "February" "1995" "14:52:32" "GMT" "Philipp Hoernes" "hoernes@sun25.mpifr-bonn.mpg.de" nil "68" "Overlays of CCD and radio images - the solution!" "^From:" nil nil "2" nil nil (number " " mark " Philipp Hoernes Feb 28 68/2312 " thread-indent "\"Overlays of CCD and radio images - the solution!\"\n") nil] nil) Newsgroups: sci.astro Path: solitaire.cv.nrao.edu!hearst.acc.Virginia.EDU!portal.gmu.edu!europa.eng.gtefsd.com!news.mathworks.com!zombie.ncsc.mil!news.duke.edu!news-feed-1.peachnet.edu!gatech!howland.reston.ans.net!Germany.EU.net!unibwh.unibw-hamburg.de!news.rrz.uni-hamburg.de!news.dkrz.de!news.dfn.de!RRZ.Uni-Koeln.DE!news.rhrz.uni-bonn.de!mpifr-bonn.mpg.de!sun25.mpifr-bonn.mpg.de!hoernes Message-ID: <1995Feb28.145232.11555@mpifr-bonn.mpg.de> Nntp-Posting-Host: sun25 Organization: Max-Planck-Institut f"ur Radioastronomie References: <1995Feb17.124140.13664@mpifr-bonn.mpg.de> Lines: 68 From: hoernes@sun25.mpifr-bonn.mpg.de (Philipp Hoernes) Sender: news@mpifr-bonn.mpg.de Subject: Overlays of CCD and radio images - the solution! Date: Tue, 28 Feb 1995 14:52:32 GMT How to produce overlays of CCD and radio images? ------------------------------------------------- After some time of learing to handle the various software packages and after a lot of kind help from sci.astro - thanx to Don Wells and Eric Greisen of the NRAO - I am now ready to post a little documentation on how it is done. Let's assume we have an optical image from a CCD observation and a radio (e.g. VLA) image. The CCD image will then be in pixel coordinates, the VLA image in RA-DEC coordinates and SIN projection. We want to overlay the images and make quantitative comparisions possible. Here's what to do: 1) We need to determine the proper sky coordinates of the CCD image. Make up a list of objects with known coordinates. Find the coordinates of these objects in the CCD frame. This can be done in MIDAS using CENTER/GAUSS. 2) Now make up two ASCII files containing the coordinates of the chosen reference objects - one in RA/DEC, on in pixel coordinates. list 1, sky coord.: 10.0623 40.1285 1 ;RA/DEC/identification of object 9.55863 41.4568 2 10.3603 41.7723 3 10.8315 41.2638 4 9.96267 41.6891 5 9.97363 41.4263 6 list 2, pixel coord.: 1458 14 1 ;X/Y/idtification of object 2008 2400 2 912 2904 3 325 1978 4 1446 2784 5 1450 2324 6 Now load these lists into MIDAS with CREATE/TABLE. 3) Use the MIDAS command ALIGN/IMAGE to compute a transformation matrix from pixel to sky coordinates. 4) Use the MIDAS command REBIN/ROTATE to transform your CCD image to the new coordinates. 5) Edit the FITS header of the new image and set the types of axis 1 and 2 to 'RA' and 'DEC'. 6) Now load the fits file of the transformed CCD image into AIPS. You can directly produce CNTR/GREYS/PCNTR-plots or use HGEOM to bring the CCD image to the same grid and the same projection as the radio image. For any quantitative comparisions this is necessary. If the astronometry is done carefully, an accuracy of the overlay of better thean 1'' an be archieved, at least that's what the MIDAS peaple claim. Don Wells informed me that the same method should also apply for IRAS IR and Einstein X-ray images, for ROSAT X-ray images MIDAS even offers special support - you won't even have to worry about astronometry at all. If you have problems - feel free to mail. Philipp