How to Apply Distortion Map

How to Apply the Distortion Map File †

The distotion map can be simply applied by IRAF ccsetwcs command;

ccsetwcs (image file) (s11a-band.db) (s11a-band.coo)

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How the Files are Made †

The distortion map is measured using the data of galactic plane, where the number density of stars are high.
The coordinates of the detected stars are matched with those in the 2MASS catalog (which are written in s11a-band.coo), and the distortion map (s11a-band.db) is produced by IRAF ccmap command with 5th order polynominal;

ccmap s11a-band.coo s11a-band.db lngunit="degree" latunits="degrees" projection="tnx" xxorder=6 xyorder=6 yxorder=6 yyorder=6 maxiter=3 reject=4

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