Lauren MacArthur has found some cases where a TAN-SIP SkyWcs is not written as TAN-SIP to FITS metadata (instead a local TAN approximation is used). The attached file is a program showing an example. I have reported the issue to David Berry in hopes he can fix it or suggest a workaround.
This issue actually consists of two parts:
- Normal TAN-SIP WCS cannot be written as FITS-WCS header cards. David Berry has implement a fix for that problem.
- WCS rotated by rotateWcsPixelsBy90 cannot be written as FITS-WCS. I have split that into a separate ticket: