RA&DEC residuals

[Ning B]

I have some images ,FOV is 2.3°×1.5°

I use wcs-xy2rd to get the ra,dec (SIP=3),and crossmatch with gaiadr2 catalog 

here is my residuals picture ,I can't explain this problem about ra's residual

thanks for your any help

 

[Dustin Lang]

Hi,

You could try creating a "quiver plot" -- plot in RA,Dec or in pixel coordinates, and at the position of each matched star, plot an arrow showing the delta-RA,delta-Dec.

If the SIP solution is wrong, you should see nearby arrows all pointing in the same direction, and then the direction slowly changing as you move around the image.

cheers,

dustin

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