ISOCAM Interactive Analysis User's Manual Version 5.0 - ISO - ESA

16.5. CDS DATA EXTRACTION 197
16.5 CDS data extraction
This section describes ways in which you can examine the contents of a CDS (remember that
a CDS is a CIA data structure which holds CAM calibration data – see Section 15.3). The
different types of calibration data (i.e. CAL-G files) and the CDS name for each is given in
Table 15.3.2 on page 173).
Let’s assume you want to find out (without using find best psf - see Section 20.12.2) what
PSFs we have for an observation configured with a 3” PFOV and the LW2 filter.
1. Firstly, you have to read in the LW PSF CDS:
CIA> psf_cds = cds_read( ’lwpsf’ )
2. Secondly, you have to know the LW2 filter wheel position and the LW lens wheel position
for the 3¨PFOV. You can find this information either in the ISOCAM documentation (e.g.
ISOCAM User’s Manual), in the CIA files hk wheels n.txt (see Section 15.4.3) or with the
function convert wheel back:
CIA> lw2_position = convert_wheel_back( ’LW FILTER’, ’LW2’ )
CIA> pfov_position = convert_wheel_back( ’PFOV LW’, 3.0 )
3. As described in Section 15.3.2, all calibration data reside in the .DATA substructure. To
extract .DATA from our PSF CDS:
CIA> data = cds_get( ’data’, psf_cds )
4. Inside this substructure you will find the cube DATA(*).IMAGE, and the arrays
DATA(*).PFOV and DATA(*).FCVF. Respectively, these hold a variety of PSFs with
their corresponding lens wheel positions and PFOVs. Using the IDL command WHERE
we can pick out the PSFs that we require.
CIA> nn = where( ( DATA.FCVF eq lw2_position ) AND $
CIA> ( DATA.PFOV eq pfov_position ) )
CIA> psf = data[nn].image[*,*,0]
Now the variable psf will hold a cube of PSF images corresponding to the CAM configuration
of filter wheel LW2 and a PFOV 3¨. You could preview these with x3d:
CIA> x3d, psf
16.6 Manipulating CIA data structure history
The processing applied within CIA to CIA data structures, also known as the history, is recorded
in the CIA data structure field PROCESS. The following sections will show you how to extract
and replace this field.