load_data segfaults when WCSNAME is present in the header but blank

[mattkbrown]

Description

Expected behavior

Actual behavior

When loading a fits file through load_data() the loader throws a segfault if WCSNAME is defined in the header but left blank. Giving WCSNAME a throwaway value of '' or None seems to get around this. I don't expect this to affect too many people as it likely will only be encountered by instrument teams during their development phase, eg they know they need a WCS so they put it into their header writer, but have not developed the instrument/code enough to fill it out.

Steps to Reproduce

1. write WCSNAME to your fits file but do not give it any value.
2. try to load the file through ginga.util.loader.load_data
3. et voila. core dump.

# Put your Python code snippet here.

System Details

Linux-6.14.0-37-generic-x86_64-with-glibc2.39
Python 3.12.3 (main, Nov 6 2025, 13:44:16) [GCC 13.3.0]
Numpy 1.26.4
astropy 6.0.0
Scipy 1.11.4
Matplotlib 3.6.3
QtPy 2.4.1
Ginga 5.0.0

[ejeschke]

Hi @mattkbrown, thanks for reporting this. Is this actually seqfaulting in astropy.wcs? If so, that is probably an upstream issue.

[pllim]

Did someone say astropy? Are you able to get some more info out of the segfault with gdb? If you suspect the cause is astropy, please try to run the load data part outside of Ginga and see if you get the same segfault.

[pllim]

That said, if you are writing an invalid FITS file that violates either the FITS or FITS WCS standards, then all bets are off.

[ejeschke]

Since we use astropy.fits to open the file, and astropy.wcs to create the WCS from the header, unless this is segfaulting later in Ginga (unlikely), I suspect this is an issue with astropy and not with Ginga. I'd like to try to reproduce this, but I'm a little unsure how to create the WCSNAME keyword without a value, since the usual methods of writing those keywords using astropy or fitsio require one to provide a value just to include the keyword. I suspect you'd have to do something with CFITSIO. @mattkbrown, can you provide a sample FITS file?