[fitsbits] updates to the FITS standard document

[Erik Bray]

On 06/22/2015 09:19 PM, Mark Calabretta wrote:
> On Mon, 22 Jun 2015 10:16:41 -0400
> Erik Bray <embray at stsci.edu> wrote:
>
> Erik,
>
>> I believe that the INHERIT keyword convention, in particular, is *not* familiar
>> to most users of FITS in large part because many readers ignore it, and it is
>> benign when ignored.
>
> Given the context, I take it that you meant to say "malign" here,
> rather than "benign".

No, I did mean that it is benign when ignored.  STScI is, I'm told, partially 
responsible for creating this keyword in the first place.  And yet even STScI's 
own FITS software has almost always chosen to ignore its presence.

I suppose if you absolutely needed the keyword to be heeded, ignoring it would 
be a problem.  But the common consensus seems to have been that *not* ignoring 
it causes even more problems.  So as it is there is some custom software that 
checks for INHERIT where it does matter for some particular instrument's data 
model.  But for generic FITS files it doesn't seem to be a big deal.

Erik

>> Suddenly requiring it to be interpreted would be very surprising to many users,
>> and even if support for it were implemented I anticipate "bug" reports from
>> users surprised that keywords that don't physically appear in some header are
>> suddenly showing up (somehow...the other problem with the INHERIT convention, as
>> documented, is that its interpretation by software is unspecified, which I
>> believe to be dangerous and user-hostile).
>>
>> If I had a vote it would be "NO" on the INHERIT convention--the others I think
>> have better existing support in the community and are benign and/or
>> well-specified.  But I think this deserves more time for discussion.
>
> Regards,
> Mark Calabretta
>