written by:-
August 1998
(Last modified 19th August 1998)
SuperCOSMOS data files are very large, and are generally supplied in compact, unformatted binary files for speedy access and efficient storage (see the Beginner's Guide for more details). This data format is non-standard, and internal to the SuperCOSMOS project. Users may wish to port their data into any one of a large number of software packages that manipulate images and/or catalogues (eg. IRAF , GAIA , KAPPA , CURSA , FTOOLS ) and the Flexible Image Transport System (FITS) allows easy export of data once they are in the required FITS format. This document describes two utilities for reformatting pixel and/or image parameter data into FITS images and/or tables. These utilities adhere strictly to the FITS standard via William Pence's FITSIO routines and are written in standard Fortran 77. The code is available for you to ftp to your home institution to reformat any unformatted SuperCOSMOS data.
% ftp ftp.roe.ac.uk username: anonymous password: your email address ftp> binary ftp> cd pub/nch/code ftp> get fits.tar.gz ftp> byethen uncompress and unpack using the following:
% gunzip fits.tar % tar -xvf fits.tarUsers at sites where the STARLINK Software Collection is installed can then compile the code as follows:
% f77 iam2fits.f -L/star/lib `fitsio_link` `sla_link` -o iam2fits % " pix " " " " pixNon-Starlink users can obtain the source code for the FITSIO and SLALIB positional astronomy libraries from those indicated URLs. Any comments/suggestions/queries/bug reports concerning the codes should be sent to N.Hambly (nch):
% ls /data1/nch/R12345 iam.srtrd hkfile.lis residual.corrns mmdata . . . %where the directory "mmdata" contains the individual lanes of pixel data (see the Beginner's and Introductory data processing guides for more details). If files have been renamed or moved, then they should be restored to their names and relative directories as detailed above (alternatively, you could alter the code to prompt for these filenames). Files supplied on EXABYTE or DAT tapes should unpack from the tape archive as above.
% ./iam2fits Path-name of measurement: /disk1/nch/UKR444 Size of square region to extract: (arcmin; 0.0 to convert entire IAM file to FITS format) 0.0 Output fits file: /disk1/nch/UKR444/iam.fits No. of IAM records written to FITS file: 598523 %Note that the code will always write a minimal FITS header detailing the columns of the output FITS table; in addition, an attempt will be made to write "housekeeping" information from the file hkfile.lis. This is not required by the FITS standard, and is not essential to further manipulation of the data; however it may be useful at some later stage in data reduction. If the required ASCII housekeeping file is not found, then a warning is issued but the routine continues execution.
% ./pix2fits Path-name of measurement: /disk1/nch/UKR444 Extent of scan (xmin, xmax, ymin, ymax): 16.22 338.78 16.22 338.78 Centre co-ordinates of region to be extracted: 13 34 59.04 -27 30 15.05 Equinox of co-ordinates (0=1900, 1=B1950, 2=J2000): 2 Size of square image to extract (arcmin): 5.0 Output pixel values in raw transmission (t) or intensity (i)? t Output FITS filename: obj1.fits Number of records read from IAM file: 598523 No. of IAM records written to FITS file: 375 %Once again, a minimal (required) FITS header is written, but housekeeping information will also be written if available (note that the extent of the measurement is normally as detailed above, but can be obtained from the housekeeping file). Two other useful features of the code are as follows: World Co-ordinate System (WCS) FITS keywords will be written to the header based on the astrometric solution used in the IAM file. This is particularly useful if displaying the image using utilities such as SAOimage TNG or GAIA (see below) which then give a continuous display of the cursor position in celestial co-ordinates (note that old versions of SAOimage written before the Greisen and Calabretta FITS WCS proposal will not necessarily read and/or use all the WCS keywords correctly). The other useful feature is that the IAM data corresponding to the region specified (or a 5x5 arcminute region, whichever is the larger) will be written as a FITS table in an extension after the image. Moreover, a binary index file of pointers to those images is also created, which can be used as detailed below. Note that pix2fits provides an option to output pixel values in raw "transmission" units or in intensity units (for more information concerning photometry from photographic plates, see the Photometry data processing guide ). Be aware that the intensity scaling is somewhat arbitrary - a "gamma" is assumed by the code (and can be changed in the source code if you wish to expermient); in any case, for various reasons the dynamic range of the image is limited when compared to, for example, CCD data.