[AstroPy] Pywcs not reading transformation matrix correctly
Oliver King
ogk@astro.caltech....
Thu Jul 26 11:54:52 CDT 2012
Hi,
I've discovered what I think is a bug in the pywcs module in astropy. I have a FITS file with a WCS that contains these parameters:
CRVAL1 = 343.485065456 / RA of reference point
CRVAL2 = 16.1466891384 / DEC of reference point
CRPIX1 = 1094.26737976 / X reference pixel
CRPIX2 = 1037.56068399 / Y reference pixel
CUNIT1 = 'deg ' / X pixel scale units
CUNIT2 = 'deg ' / Y pixel scale units
CD1_1 = -7.75889930453E-05 / Transformation matrix
CD1_2 = 4.5042903792E-07 / no comment
CD2_1 = -3.9690360471E-07 / no comment
CD2_2 = -7.76314691533E-05 / no comment
Notice that the transformation matrix parameters are in exponential notation. However, when I read the WCS using astropy I get these parameters:
In [14]: wcs.printwcs()
WCS Keywords
CD_11 CD_12: -7.7588993045299999 4.5042903790000004
CD_21 CD_22: -3.9690360400000002 -7.7631469099999997
CRVAL : 343.48506545599997 16.146689138399999
CRPIX : 1094.26737976 1037.5606839
NAXIS : 2048 2048
It has ignored the exponential notation. If I manually edit the transformation matrix parameters in the header to remove the exponential notation it reads in the WCS correctly.
Is this a known bug? Is there a workaround or do I need to manually edit my FITS file headers?
Cheers,
Oliver
------
Oliver King
Astronomy Department, Caltech
+1-626-395-4197
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