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Changing image center pixels
07-21-2014, 21:02
Post: #1
Changing image center pixels
Hi. I would like to generate an output image in MOL projection. We need the full range of RAs, but only limited Dec values since our telescope in in the Southern Hemisphere (and so cannot see Dec > 20deg).

I want the MOL projection to be centered at RA=12h, Dec=0. This gives the best display of the output coordinate grid (it may not be quite ideal since it distorts the zenith, but this is mostly for making nice images). However, I don't want the reference pixel to be at (Nx/2,Ny/2) where Nx and Ny are the image sizes in x and y. Instead I'd like to move the reference pixel to be offset in Dec, such that my image covers the Dec range of my telescope without wasting pixels.

I.e., I want to be able to specify both:

CRVAL1,CRVAL2 (which are done through the CENTER keyword)

and:

CRPIX1,CRPIX2

An example would be:

NAXIS1 = 27648
NAXIS2 = 9216
LONPOLE = 1.800000000000E+02
LATPOLE = 9.000000000000E+01
CTYPE1 = 'RA---MOL'
CRVAL1 = -1.800000000000E+02
CDELT1 = -1.250000000000E-02
CRPIX1 = 1.382500000000E+04
CUNIT1 = 'deg '
CTYPE2 = 'DEC--MOL'
CRVAL2 = 0.000000000000E+00
CDELT2 = 1.250000000000E-02
CRPIX2 = 6.738000000000E+03
CUNIT2 = 'deg '


Is there a way to specify CRPIX1/CRPIX2 or equivalently specify how I want to center my image?

David
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