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a problem of scale: FSCALE_DEFAULT
02-15-2008, 11:31
Post: #1
a problem of scale: FSCALE_DEFAULT
Hi,

I was trying to combine sky flats with swarp, but I found I can't make the scale right. So, I tried to do a simple test by combining a few identical images with FSCALE_DEFAULT set to some values, but I am really confused with the result.

Here is the command I used:
swarp a.fits,a.fits,a.fits,a.fits -c default.swarp -HEADER_SUFFIX .head -BLANK_BADPIXELS N -WEIGHT_IMAGE a.wm,a.wm,a.wm,a.wm -PROJECTION_TYPE TAN -IMAGEOUT_NAME test.fits -SUBTRACT_BACK N -RESAMPLE N -COMBINE_TYPE MEDIAN -WEIGHT_TYPE MAP_WEIGHT -WEIGHTOUT_NAME test.weight -FSCALE_DEFAULT 0.5,0.5,0.5,0.5 -FSCALE_KEYWORD FFF -FSCALASTRO_TYPE NONE

(the default.swarp is generated from swarp -dd)

I found the counts in test.fits are roughly 1.5 of that in a.fits. It is strange that the ratio is not 0.5, and the ratio is not a constant, nither. Though, the distribution is quite narrow (1.40 to 1.53). Since the .head files are the original header of a.fits, there should be no any projection effect, and I have set the FSCALASTRO_TYPE to NONE.
On the other hand, if I set the FSCALE_DEFAULT to 1.0, then the result is exactly the same with a.fits.

May I ask if anyone knows what's going on?

Cheng-Jiun

P.S., I am using swarp-2.17.1
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a problem of scale: FSCALE_DEFAULT - cjma - 02-15-2008 11:31

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