[fitsbits] INF/NAN as header values?

[Steve Allen]

On Fri 2013-06-07T12:44:44 -0700, Tim Pearson hath writ:
> I can think of no use-cases in which it would be appropriate for the
> value of a FITS header keyword to be Inf: perhaps someone else can?

I do not want to rule out that possibility, but I also do want not to
break existing FITS readers.

> There are cases where the value NaN might be appropriate, but in
> such cases I think it must be better to indicate ignorance by omitting
> the keyword.

> So I do not think keyword-values Inf and NaN should be added to the
> FITS standard.

We do have the concept of "null" or "undefined" header keywords; e.g.

MYKEYWRD=       / absence of value after equals and before slash

Rather than create files that violate the existing standard (and
especially for mandatory and reserved keywords with defined data type)
I would prefer writing a "null" value with a comment; e.g.
MYKEY001=       / +Inf
MYKEY002=       / -Inf
MYKEY003=       / NaN
For most situations simply writing a "null" value is already a strong
flag that interpreting the value requires special care.

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