Help with WCS
Diego Farías wrote on Apr 28, 2015
Hi everyone, I'm new in this forum and I would like you to give me some advices about a problem I've had with WCS:
I have a set of FORS2 polarimetric images, and for some reason the WCS is messed up in the slits; for this I'm using a reference image (with no polarimetric optics) of the same field, with a GOOD WCS. In the beginning, I just needed to align slits which I've done (years ago) with imalign, and I got good results, but as I didn't have a WCS (from slits) I couldn't properly reconstruct my image.
What I want to do now is using the WCS of the reference image and "copying it" to my slits after aligning reference's section with
the slits,
Any idea how to do this? I've tried using wcscopy, but it doesn't work properly and I think I should use something like msctpeak/ccmap, but I'm not used to those tasks yet.
Thanks a lot
Diego
PS: I've tried to use catalogs/astrometry.net, but my images are really small and the latter fails solving fields.
Matrix wrote on Apr 29, 2015
Do you want to add a wcs to your fits image? If so, I recommend you a website: http://blogs.thewehners.net/liz/posts/353-adding-a-wcs-to-your-fits-image, you can do it as it says.
Diego Farías wrote on Dec 16, 2015
Hi Matrix, thanks for your answer.
I've tried that ( I 'made' a 'catalog' with the information I had from a reference image), but
when I use CCMAP I don't have a good plate solution for my image (it is the same field of reference image after all, that means, I should be able to get a 'similar' WCS). For sure is my mistake, because not only I got wrong celestial coordinates; also pixel scale is way off, rotation fitting parameter are not zero (not even close to zero) and etc...
Is it naive to think if I have almost identical images (just x,y shifts ), one with a good WCS and the other with a messed up, I should be able to get a 'close' WCS doing the procedure on that webpage? (i.e. getting a catalog of stars from the image with good WCS, knowing the shifts between the images, knowing also the reference point of the good image and the projection)
I'm sorry for the question, but I think I'm a bit confused and amazed for the results.
PD: I know that with the information I have I could 'simply' shift my images and copy and paste the WCS, but I don't want to do that for multiple reasons.
Diego
Last post on Dec 16, 2015