[fitsbits] INF/NAN as header values?

[Erik Bray]

I originally sent this message a few months ago and never got any replies.  Now 
based on recent activity I'm thinking maybe the mailinglist was having issues? 
So trying again. Apologies if this is a duplicate.


-------- Original Message --------
Subject: INF/NAN as header values?
Date: Mon, 8 Apr 2013 15:15:21 -0400
From: Erik Bray <embray at stsci.edu>
To: <fitsbits at nrao.edu>

Hello all,

I've had a few different issues reported against PyFITS lately regarding INF/NaN
as values in FITS headers (that is, as float literals, without quotation marks
around them).

In particular, reading files that contain values like this fails in PyFITS, and
writing those values to a header currently has undefined behavior (though upon
writing to disk the header is reported as invalid).  And according to a strict
reading of the current FITS standard, specifically section 4.2.4, this is
correct:  INF and NaN are not valid formats for header values.

I have a suspicion that this was at one time intentional--not all systems may
have had representations for those values in their floating point
implementations.  But by today's standards it feels like an oversight.  It was
pointed out to me that IDL allows saving INF/NaN as header values, but the way
it writes them violates the FITS standard.  But several such files appear to be
present in the wild, so I'm considering going and letting PyFITS allow this too.

Are there any thoughts/feelings on this?  Should this be corrected in a future
version of the standard?

Thanks,

Erik