Astropy WCS: "IOError: Header missing END card."

Question

I'm trying to convert WCS to pixels using astropy, but when I try to read in the image:

from astropy import wcs

w = wcs.WCS('image_file.fits')

I get the following Exception:

*WARNING: Unexpected extra padding at the end of the file.  This padding may not be preserved when saving changes. [astropy.io.fits.header]
Traceback (most recent call last):
  File "make_stamps.py", line 29, in <module>
    w = wcs.WCS(image_file)
  File "/Users/anaconda/lib/python2.7/site-packages/astropy/wcs/wcs.py", line 385, in __init__
    fobj = fits.open(header)
  Fhttp://stackoverflow.com/posts/41513868/editile "/Users/anaconda/lib/python2.7/site-packages/astropy/io/fits/hdu/hdulist.py", line 139, in fitsopen
    return HDUList.fromfile(name, mode, memmap, save_backup, cache, **kwargs)
  File "/Users/anaconda/lib/python2.7/site-packages/astropy/io/fits/hdu/hdulist.py", line 281, in fromfile
    save_backup=save_backup, cache=cache, **kwargs)
  File "/Users/anaconda/lib/python2.7/site-packages/astropy/io/fits/hdu/hdulist.py", line 839, in _readfrom
    hdu = _BaseHDU.readfrom(ffo, **kwargs)
  File "/Users/anaconda/lib/python2.7/site-packages/astropy/io/fits/hdu/base.py", line 423, in readfrom
    **kwargs)
  File "/Users/anaconda/lib/python2.7/site-packages/astropy/io/fits/hdu/base.py", line 483, in _readfrom_internal
    header = Header.fromfile(data, endcard=not ignore_missing_end)
  File "/Users/anaconda/lib/python2.7/site-packages/astropy/io/fits/header.py", line 451, in fromfile
    padding)[2]
  File "/Users/anaconda/lib/python2.7/site-packages/astropy/io/fits/header.py", line 520, in _from_blocks
    raise IOError('Header missing END card.')
IOError: Header missing END card.*

I got this error before when using just fits.open() but was able to solve the problem by adding "ignore_missing_end=True". But, "ignore_missing_end" doesn't seem to be a argument of the wcs class. How can the image be read with astropy.wcs.wcs?

Answer 1

That astropy.wcs.WCS can take a filename is just a convenience option so it's not really surprising that you can't pass (all) parameters that astropy.io.fits.open accepts to this function as well.

However it's quite easy to create a WCS with a astropy.io.fits.Header. So you can open the file, extract the relevant header and create the WCS yourself:

from astropy.io import fits
from astropy.wcs import WCS

with fits.open('your_file.fits', mode='readonly', ignore_missing_end=True) as fitsfile:
    # if you want the first extension, otherwise change the [0].
    wcs = WCS(fitsfile[0].header)  
# Now you can use your WCS, for example:
print(wcs)