Monday, April 2, 2012

WCS to pixel values and vice versa in Python

It's often necessary to convert pixel coordinates within a binary image to physical(ra, dec) sky coordinates. For instance, one might need to find brightness at the central pixel of the galaxy, calculate flux, any photometry-related task would do, actually. I used astLib.astWCS for this purpose, though I think pywcs might work just as well.
from astLib import astWCS


center = WCS.wcs2pix(ra, dec)
print center
print 'brightness at the galaxy center', img[center[1], center[0]] 
#thanks, numpy -- python indexes arrays ass-backward (or, rather, column-backward) for some reason. One have to be careful not to swap them.

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