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

20.15. ADVANCED PROJECTION 265
20.15.5 Distortion correction for staring, beam-switch and CVF observations
Using the routines project struct, project bs and project cvf also the exposures of staring
observation can be corrected for distortion.
In the following example we discuss distortion correction for a staring observation. Beamswitch
and CVF observations are treated in a similar way. Assuming the EXPOSURE in has
been generated the usual way, it will have 32×32 pixels (see left picture in Figure 20.9).
CIA> help, staring_pds.image
FLOAT = Array[32, 32]
Distortion-correction and magnification by the factor 2 will be performed by the following
command:
CIA> project_struct, staring_pds, magnify=2
The resulting EXPOSURE has now 67×65 pixels
CIA> help, staring_pds.image
FLOAT = Array[67, 65]
Additionally, the original fields .IMAGE, .RMS and .NPIX were renamed to .OLD IMAGE,
.OLD RMS and .OLD NPIX, while .RMS and .NPIX contain now information corresponding
to .IMAGE.
As usual, export to a FITS file is done with CIA’s imagette2fits. This routine will place
the data in the PDS field .IMAGE into the primary array of the FITS file.
Figure 20.9: Comparison of standard vs. distortion corrected staring observations
Left: Standard 32×32 EXPOSURE
Right: Distortion-corrected and magnified EXPOSURE (67×65 pixels). Due the rebinning of
the pixels, the flux per pixel is reduced by the factor 4.