Reprojecting Coordinates of a Solar System Object
[CIAO 3.4 Science Threads]
OverviewLast Update: 1 Dec 2006 - reviewed for CIAO 3.4: no changes Synopsis: When an object is observed moving with respect to the observer, e.g. a planet or comet, the resulting event file looks "blurred" when viewed in (x,y) coordinates. The sso_freeze tool reprojects the coordinates to the frame of the object, eliminating this blurring. Purpose: To reproject coordinates from the frame fixed to the celestial sphere to a reference frame which is fixed to the moving solar system object (SSO). Read this thread if: you are working with any observation of a solar system object. |
Contents
- Choosing the Ephemeris Files
- Run sso_freeze
- Display the Results
- Parameter files:
- History
- Images
Choosing the Ephemeris Files
Sample ObsID used: 1463 (ACIS-S, Jupiter)
File types needed: evt2; eph1
There are two ephemeris input files needed for the tool to run. One is the spacecraft ephemeris file (scephemfile) and the other is the SSO ephemeris file (ssoephemfile).
Due to a bug in ChaSeR, it is necessary to obtain both of these files from the CDA FTP site.
The ephemeris files are selected based on the start time (TSTART) of the observation:
unix% dmkeypar acisf01463N002_evt2.fits TSTART echo+ 59968797.485273
Now connect to cda.harvard.edu, using the login "anonymous" and your email address as the password:
unix% ftp cda.harvard.edu Connected to cda. 220 cda FTP server (Version wu-2.6.1(1) Mon Aug 7 15:20:43 EDT 2000) ready. Name (cda.harvard.edu:): anonymous 331 Guest login ok, send your complete e-mail address as password. Password: 230- Welcome to the FTP server at the CXC Science Center 230- 230- This server is cda.harvard.edu 230- 230-If your FTP client crashes or hangs shortly after login please try 230-using a dash (-) as the first character of your password. This will 230-turn off the informational messages that may be confusing your FTP 230-client. 230- 230-Publicly available files are in /pub 230- 230-Problems with this ftp site? Contact cxcftp@head-cfa.harvard.edu 230- 230- +---------------------------------------------------------+ 230- | | 230- | PLEASE NOTE: (ChaSeR users only) | 230- | | 230- | If the directory provided to you by ChaSeR appears | 230- | to be empty, this is a sign that your tar file is | 230- | not yet ready. Please try again in a little while. | 230- | | 230- | If your directory seems to contain several tar | 230- | files, e.g., file.tar.0, file.tar.1, ... | 230- | retrieve all files, then untar as follows: | 230- | cat file.tar.* | tar xvf - | 230- | We are limiting the size of individual files to | 230- | less than 2 GB, but these files need to be | 230- | concatenated before submitting them to tar. | 230- | | 230- +---------------------------------------------------------+ 230- 230 Guest login ok, access restrictions apply. ftp> cd /pub/arcftp/bary/ephem 250 CWD command successful. ftp> ls 200 PORT command successful. 150 Opening ASCII mode data connection for file list. asteroid_1998_wt24f124416300N001_eph1.fits comet_1999_s4_linearf079920300N001_eph1.fits comet_1999_s4_linearf081475500N001_eph1.fits ..(cut).. jupiterf059875200N001_eph1.fits jupiterf059875200N002_eph1.fits jupiterf093312000N001_eph1.fits jupiterf162475200N001_eph1.fits marsf110592000N001_eph1.fits moonf110563500N001_eph1.fits moonf112492800N001_eph1.fits moonf117504000N001_eph1.fits moonf200016000N001_eph1.fits moonf202550400N001_eph1.fits moonf207316800N001_eph1.fits orbitf050397000N001_eph1.fits orbitf050420100N001_eph1.fits orbitf050745900N001_eph1.fits orbitf052088700N001_eph1.fits orbitf053208300N001_eph1.fits orbitf054122700N001_eph1.fits ..(cut).. orbitf246888300N001_eph0.fits orbitf246888300N001_eph1.fits saturnf166665600_eph1.fits saturnf190944000N001_eph1.fits saturnf191505600N001_eph1.fits titanf158112000N001_eph1.fits uranusf145120000N001_eph1.fits venusf095299200N001_eph1.fits 226 Transfer complete. 21088 bytes received in 1.2 seconds (17.64 Kbytes/s) ftp>
The files that begin with "orbit" are spacecraft ephemeris files; the SSO ephemeris files are identified by the object name and file start time. In each case, we want to choose the file that has the highest start time less than the start time of the data (59968797):
ftp> ls orbitf059* 200 PORT command successful. 150 Opening ASCII mode data connection for file list. orbitf059227500N001_eph1.fits orbitf059486700N001_eph1.fits orbitf059832300N001_eph1.fits 226 Transfer complete. remote: orbitf059* 93 bytes received in 0.0014 seconds (66.49 Kbytes/s) ftp> get orbitf059832300N001_eph1.fits ftp> ls jupiter* 200 PORT command successful. 150 Opening ASCII mode data connection for file list. jupiterf059875200N001_eph1.fits jupiterf059875200N002_eph1.fits jupiterf093312000N001_eph1.fits jupiterf162475200N001_eph1.fits 226 Transfer complete. remote: jupiter* 132 bytes received in 0.03 seconds (4.36 Kbytes/s) ftp> get jupiterf059875200N002_eph1.fits 200 PORT command successful. 150 Opening ASCII mode data connection for jupiterf059875200N002_eph1.fits (63360 bytes). 226 Transfer complete. local: jupiterf059875200N002_eph1.fits remote: jupiterf059875200N002_eph1.fits 63462 bytes received in 0.13 seconds (462.57 Kbytes/s)
If there is more than one version of a file - e.g. N001 and N002 - choose the newest (higher number) version available.
So the two ephemeris files for this observation are orbitf059832300N001_eph1.fits and jupiterf059875200N002_eph1.fits.
Run sso_freeze
Once you have the necessary input files, you are ready to run the tool:
unix% punlearn sso_freeze unix% pset sso_freeze infile=acisf01463N002_evt2.fits unix% pset sso_freeze scephemfile=orbitf059832300N001_eph1.fits unix% pset sso_freeze ssoephemfile=jupiterf059875200N002_eph1.fits unix% pset sso_freeze outfile=frozenjupiter.fits unix% sso_freeze Input event file or stack (acisf01463N002_evt2.fits): Input spacecraft ephemeris file (orbitf059832300N001_eph1.fits): Input solar system object file (jupiterf059875200N002_eph1.fits): Output event file name (frozenjupiter.fits):
The contents of the parameter file may be checked using plist sso_freeze.
Display the Results
The new object-centered coordinates are stored in the ocx and ocy columns of the file. When displaying the "frozen" image, we must specify to bin on those columns (note that the binning syntax for ds9 is not the same as for the DM):
unix% ds9 "frozenjupiter.fits[bin=ocx,ocy]" &
Alternatively, the image can be loaded in the usual way into ds9:
unix% ds9 frozenjupiter.fits &
Then the binning may be changed with the "Bin -> Binning Parameters..." dialog box. Choose "ocx" and "ocy" with the buttons in the "Bin Columns" section.
Figure 1 ![[Link to Image 1: Comparison of original and "frozen" images]](../../imgs/imageicon.gif){kind=small}
shows the original and
"frozen" images side-by-side.
Parameters for /home/username/cxcds_param/sso_freeze.par
#----------------------------------------------------------------------
#
# sso_freeze.par- Parameter file for planetary transformations routine
#
#----------------------------------------------------------------------
infile = acisf01463N002_evt2.fits Input event file or stack
scephemfile = orbitf059832300N001_eph1.fits Input spacecraft ephemeris file
ssoephemfile = jupiterf059875200N002_eph1.fits Input solar system object file
outfile = frozenjupiter.fits Output event file name
(logfile = STDOUT) debug log file ( STDOUT | stdout | <filename>)
(scale = 0) Image pixel scale (km/pixel, 0=angular coords)
(lookuptab = ${ASCDS_CALIB}/dmmerge_header_lookup.txt -> /soft/ciao/data/dmmerge_header_lookup.txt) lookup table
(clobber = no) Overwrite existing output dataset with same name?
(verbose = 0) debug level (0-5)
(mode = ql)
|
History
| 03 Jan 2005 | reviewed for CIAO 3.2: no changes |
| 16 Dec 2005 | updated for CIAO 3.3: bug in ChaSeR means that orbit ephemeris files must be retrieved from the CDA FTP site |
| 01 Dec 2006 | reviewed for CIAO 3.4: no changes |
