[AstroPy] FITS files and column descriptions

Yannick Roehlly yannick.roehlly at lam.fr
Thu Nov 7 16:20:37 EST 2013

Hi all,

I have some remarks / questions concerning the column descriptions in
FITS table files (and VO).

1. Long column description

The FITS format requires that a column description must be 68
characters or less. Some tools like topcat / stills allows longer
descriptions because they use a kind of VO-table metada section in the
FITS header. If you open such file with astropy.io.fits and save it
again, you loose the long description. In fact, it's not an astropy
problem as these description as not in the "real FITS" column
descriptions in the header (TCOMxx), it is just because astropy does
not save the "VO-table" part of the topcat file.
Maybe it's worth raising a warning when opening such files, like "Hey,
you may loose metadata!" because one may be surprise not to have all
its column description.

2. astropy.table and column descriptions in FITS files

When opening a FITS file with astropy.tables(with last git checkout)
one does not have access to column descriptions. When saving an
astropy.io.table to FITS, the column description are lost. But when
opening a FITS file with description and saving it again to FITS, the
column descriptions are still here. I suppose that it's because
astropy.io.fits is under the hood. 

Is this because column description handling is not implemented or do I
miss something?

3. Column descriptions in VO-Table

When saving a table to VO-Table, astropy prettily indent the xml, e.g.

     IAU Name

But when reading these tables with topcat, this one add the spaces to
the description ("     IAU Name"). Maybe astropy should write the
description on one line.



Mystics always hope that science will some day overtake them.
		-- Booth Tarkington

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