tweak order for distortion compensation

[tano...@gmail.com]

Hi,

If I understand correctly, astrometry compensate the image distortion using SIP polynomial correction. It can be done both adding the option - -crpix-center in the solver line and the option - - tweak-order (2 by default)

Is there a best tweak order value for a  super wide field of view (10, 15 up to 20 degrees)?

Thanks

[Dustin Lang]

Hi,

--tweak-order 3

will probably help.  Beyond that, I'm not sure.  The SIP polynomial, like all polynomials, is prone to poor extrapolation, and that gets worse at higher orders.  Best is to experiment with different orders and look at the "red-green" plot to see whether the stars detected in your image (red) match up with the stars from the reference catalog (green).

cheers,

dustin

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