Name
lwscoadd -- Convert raw 6-dimensional LWS image to 2-D frame
Usage
lwscoadd input output
Parameters
- input
- List of input images to process. These must be
6-dimensional raw LWS images. Wildcards may be used to select
multiple files. An "@"-file may also be used.
- output
- List of output co-added images to create. This may be
either a list of files (in which case the number of input and
output images must match), a directory name (in which case the
output images will have the same names as the input images), or
a blank string (legal only if the CL environment variable
clobber=yes, in which case
the output images will replace the input images).
- verbose = yes
- Flag which determines whether or not to echo the actions
being taken.
Description
The
lwscoadd task takes as input a raw image
produced by the Long Wavelength Spectrometer (LWS) at the W. M. Keck
Observatory (WMKO) and outputs an image which properly combines the
various layers of the input. The raw LWS images have the following
dimensions:
- detector columns:
Index of detector column or "x" coordinate, from 1 to 128.
- detector rows: Index of detector row or "y" coordinate, from 1 to 128.
- chpbeams:
Index of chop beam, 1 for on-source and 2 for off-source.
- savesets:
Index of the save set; i.e., number of disk writes during a nod set.
- nodbeams:
Index of nod beam, 1 for on-source and 2 for off-source.
- nodsets:
Index of the nod set; i.e., number of nods during the exposure.
Processing consists solely of subtracting the appropriate chop-off
beams from their corresponding chop-on beams, and subtracting
nod-off layers from corresponding nod-on layers; i.e., taking the
"double difference." Images are properly processed whether taken
in stare, chop, or chop-nod mode.
Examples
- To convert a single raw LWS image into an output image in
the same directory:
cl> lwscoadd lws00001.fits coadd00001.fits
- To convert a single raw LWS image into an output image of
the same name in a subdirectory named coadd/:
cl> lwscoadd lws00001.fits coadd/
- To replace all LWS images in the current directory with
their co-added versions:
cl> lwscoadd *.fits
This will only work if the CL environment variable clobber = yes.
Time Requirements
To process a 32MB raw LWS image on a lightly-loaded UltraSPARC 10
requires less than 4 seconds, which is much faster than equivalent
IDL routines.
Algorithm
The algorithm can be described as follows:
for( each line in the input image){
set default sense to "positive";
negate the sense if this layer represents the CHOP OFF beam;
negate the sense if this layer represents the NOD OFF beam;
add this line into the final array;
}
Notes
- Clobbering of the input image is supported if the CL
environment variable clobber = yes. To disable
clobbering, issue the command
cl> reset clobber = no
on the IRAF command line, or in your loginuser.cl file.
Author
Gregory D. Wirth, W. M. Keck Observatory
Support
Send questions to the
Revisions
- lwscoadd v1.1 1999-Oct-27
- Fixed bug in lwscoadd() procedure: data array not zeroed
- lwscoadd v1.0 1999-Oct-26
- Original public release.
- lwscoadd v0.0 1999-Jun-30
- Original internal release.
See Also
The IDL version of lwscoadd
The SPP program lwscoadd.x
The package wmkolws
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Last modified: Wed Jan 30 11:19:21 HST 2002