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2 Attaching modified coordinates using CCDPACK
For users of Starlink software, the calibrated coordinate information can be attached automatically to
image files using the ASTIMP command, and the file INT-WFC.ast
. This file is distributed in the
CCDPACK package (in directory $CCDPACK_DIR
, or bin/ccdpack
).
To use this facility, it is best if the files are first converted to Starlink NDF format using the CONVERT
package as follows:
% convert
CONVERT commands are now available -- (Version 1.5-4)
Defaults for automatic NDF conversion are set.
Type conhelp for help on CONVERT commands.
Type "showme sun55" to browse the hypertext documentation.
% fits2ndf in=’r10628?.fits’ out=’*’ container=true
which will convert the FITS file r106280.fits
into the NDF r106280.sdf
and so on. The Starlink
software will in fact work with FITS files, but because it converts them on the fly between FITS and
NDF formats before and after each command, this can be rather slow with files the size of WFC
frames.
Once the file is in Starlink NDF format, from the Unix C shell do the following:
% ccdpack
CCDPACK commands are now available -- (Version 4.0-16)
For help use the commands ccdhelp or ccdwww
% astimp in=’r10628?’ astfile=$CCDPACK_DIR/INT-WFC.ast reset accept
ASTIMP
======
Framesets read from file INT-WFC.ast:
FITS header "ROTSKYPA" used for rotation
N Base domain Current domain Frameset ID
-- ----------- -------------- -----------
1 PIXEL INT-WFC FITSID CHIPNAME ’A5506-4’
2 PIXEL INT-WFC FITSID CHIPNAME ’A5383-17-7’
3 PIXEL INT-WFC FITSID CHIPNAME ’A5530-3’
4 PIXEL INT-WFC FITSID CHIPNAME ’A5382-1-7’
4 NDFs accessed using parameter IN
Processing NDF /data/cass58a/mbt/data/int4/r106280
Matched with frameset ID "FITSID CHIPNAME ’A5506-4’"
Rotating additional 180 degrees
New frame in domain "INT-WFC" added
Processing NDF /data/cass58a/mbt/data/int4/r106281
Matched with frameset ID "FITSID CHIPNAME ’A5383-17-7’"
Rotating additional 180 degrees
New frame in domain "INT-WFC" added
Processing NDF /data/cass58a/mbt/data/int4/r106282
Matched with frameset ID "FITSID CHIPNAME ’A5530-3’"
Rotating additional 180 degrees
New frame in domain "INT-WFC" added
Processing NDF /data/cass58a/mbt/data/int4/r106283
Matched with frameset ID "FITSID CHIPNAME ’A5382-1-7’"
Rotating additional 180 degrees
New frame in domain "INT-WFC" added
This command sets the Current coordinate frame of the specified NDF files to the new coordinate
system
described above. As well as applying the linear and nonlinear geometry terms whose coefficients were
given, it also rotates the coordinates according to the value of the ROTSKYPA FITS header card, which
records the orientation of the turntable when the observation was made; in this case it was oriented at
180. In
this way, applying the INT-WFC.ast
file to any set of image NDF files will result in them sharing
coordinates which are related by a simple shift in X and Y coordinates, since the nonlinear optical
distortions, the exact positioning of the CCDs on the turntable, and the orientation of the turntable
itself will have been accounted for.
Once the new coordinate system has been attached to the images, then most Starlink applications will
make use of this as appropriate. If you display any of the images using KAPPA’s DISPLAY
application, the axes will show the coordinates in the new frame as in figure 3:
% kappa
KAPPA commands are now available -- (Version 0.13-7)
Type kaphelp for help on KAPPA commands
Type "showme sun95" to browse the hypertext documentation
% display r106282 style=’"grid=1,gap=500"’
If some of the frames overlap, the corresponding X and Y offsets can then easily be determined using
CCDPACK’s object matching registration facilities.
Copyright © 2000 Council for the Central Laboratory of the Research Councils
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