Reading Atlas Images
The atlas images are in a binary heap format that is not easily readable
by normal humans; think soft encryption.
We have created a standalone code that serves to both read them and as a
template library for inclusion in other codes. The code is available as: readAtlasImages-v5_4_11.tar.gz.
Compiling
1. % make clean
2. % make
If you are on a big-endian machine, remove -DSDSS_LITTLE_ENDIAN from
CFLAGS in the Makefile.
Using
% read_atlas_image -h
Usage: read_atlas_image [options] input-file row output-file
Your options are:
-? This message
-b # Set background level to #
-c # Use color # (0..ncolor-1; default 0)
-h This message
-i Print an ID string and exit
-v Turn up verbosity (repeat flag for more chatter)
If one wanted to read the r-band atlas image of an object with id=432 in
run 752, rerun 20, camcol 3, field 177, one would say:
% read_atlas_image -c 2 fpAtlas-000752-3-0177.fit 432 myAtlasImage.fits
where one should know the code that filters u,g,r,i,z are 0,1,2,3,4
respectively. The background level is an artifical offset added to all
pixels. The SDSS convention is 1000..
Developer Comments
I don't expect that many users will actually want to use the
read_atlas_image executable (although it is perfectly functional). The main
use of the product will probably be to link into custom built executables
that need to process atlas image data. I believe that the code should be
easily reused for this purpose.
If you look at the code you'll see that it actually manipulates a type
called an ATLAS_IMAGE. This contains a field called a master_mask that
contains inter alia the bounding box of the atlas image ([rc]{min,max}) in
the r band, and offsets to that band (d{row,col}).
The standalone programmes read_mask (reads fpM files) and read_PSF (reads
psField files) are similar; all three are built by the same 'make' command.
Last modified: Fri Jun 23 13:59:50 BST 2006
|