Repository navigation
Is it possible to add WCS constructor. #6371
Description
There are different wcs definitions especially for polynomial. There is Sip class for constructing tan-sip programmatically, but for TPV TPD or anything else, seems that no way to build an empty wcs with parameters initialized, even I could not find a way to modify the TPV parameters.
Activity
fockez commentedon Jul 23, 2017
I see that astropy expose the wcsprm and tabprm struct of wcslib to python, but no disprm and dpkey, is that why astropy can initial TPV only from header.
nden commentedon Jul 23, 2017
@fockez TL;DR It's not possible currently to create a TPV distortion programmatically.
To give some background on this.
wcslibdid not implement distortions until early 5.x.astropy.wcshad an implementaiton ofSIPandLookupTabledistortion long before that. This was done as a layer on top ofwcslib. Whenwcslibimplemented distortions an attempt was made to start using SIP fromwcslib. However there were issues with inverse and roundtripping of coefficients which needed to be fixed inwcslib. So this aproach was abandoned andastropy.wcscontinued usingSipfrom the python layer. As far as I can tell from thewcslibChange log this issue has not been worked out. MeanwhileTPVand the rest of the polynomials are implemented inwcslibonly. Hence there's a difference in what can be done withSipand the rest of the polynomials. Some of the relevant PRs are #3751, #3845, #3878.fockez commentedon Jul 27, 2017
I understand the difference between Sip and other polynomials. I mean, the base wcs Wcsprm is implemented, can the disprm be implemented as well? Or scheduled.
nden commentedon Jul 27, 2017
I think this was attempted in #3845 and did not quite work. I'm setting the milestone to
Futurein case someone has the time to do it.