Is there any way for SWARP to hand SIP distortion standards?

[TrystanScottLambert]

No description provided.

[ebertin]

Hi @TrystanScottLambert
Unfortunately SWarp does not yet handle SIP. If your image projection is -TAN-SIP, you might however be able to convert them to TPV using this tool. I haven't tried it though.

[TrystanScottLambert]

@ebertin Thanks so much for the reply. I gave that tool a trial a while back. It converts the WCS from the SIP to TPV which results in the headers looking like the attached header.

header.txt

When I run Swarp on these images with the converted wcs, Swarp gives me the following error for a lot of the images:
WARNING: Significant inaccuracy likely to occur in projection

And then is unable to combine them at the final step.

So I don't know if the conversion is playing nice with Swarp. Do you see anything blatantly obvious in the header due to the conversion? I'd love to write a fix if at all possible.

Thanks.

[ebertin]

Sorry for not getting back to you earlier. Yes the warning means that SWarp is not able to invert the (de-)projection to a sufficient accuracy (<<pixel) . It often means that the distortion is not bijective everywhere over the frame. It might be worth plotting the distortion pattern to check whether it looks reasonable.