Reading pyspeckit file 10074-190_HCOp.fits about specutils

[keflavich]

@shaileshahuja This is a simple 1D spectrum, but the FITS header has 3 degenerate axes. You can use wcs.sub to drop all but the spectral axis:

header = fits.getheader('10074-190_HCOp.fits')
data = fits.getdata('10074-190_HCOp.fits')
w = wcs.WCS(header)
spectral_axis = w.naxis - 1 - w.wcs.spec # w.wcs.spec is FITS-order, 0-indexed
w_spec = w.sub([wcs.WCSSUB_SPECTRAL])
# this is the general case
slices = [slice(None)] + [0 for i in range(w.naxis-1)]
spectrum = data.swapaxes(0,spectral_axis)[slices]
# in this case, this would work fine:
spectrum = data.squeeze()

pyspeckit's reader is non-general and simply assumes the first axis is the spectral one (with an override option).

[shaileshahuja]

Thanks @keflavich for your response. May I know where is this procedure to evaluate this kind of function defined? Any research paper?

[keflavich]

The WCS features are recorded in the astropy docs. They derive from WCSlib. This isn't research-level stuff, it's definitions and standards.

[shaileshahuja]

Is there any place where this standard is defined? There are a lot of WCS keywords, and I am trying to find a place where these standard are detailed, including steps to follow to derive the world coordinates from logical coordinates

[keflavich]

Yes!

The old IRAF standard is here:
http://iraf.noao.edu/projects/spectroscopy/formats/sptable.html

The FITS homepage is here:
http://fits.gsfc.nasa.gov/
especially Papers II and III; these actually define the standard officially:
http://fits.gsfc.nasa.gov/fits_wcs.html

I swear there was another link, but I can't find it right away...

[wkerzendorf]

So we figured out yesterday that most of the data contained in this file is described in http://www.aanda.org/index.php?option=com_article&access=bibcode&Itemid=129&bibcode=2006A%2526A...446..747GFUL - which I think settles this problem for now.

[keflavich]

Yes, that's the "Paper III" I was referring to.