[fitsbits] structurally compliant FITS

[Rob Seaman]

Hi Mark,

> On Jun 26, 2015, at 8:56 AM, Mark Calabretta <mark at calabretta.id.au> wrote:
> 
> On Fri, 26 Jun 2015 07:09:23 -0700
> Rob Seaman <seaman at noao.edu> wrote:
> 
> Hi Rob,
> 
>>> Also, I must point out that the simplest legal FITS file consists of
>>> SIMPLE, BITPIX, NAXIS and END keyrecords, followed by 32 blank
>>> keyrecords.  Everything else in the standard is optional.  "Optional"
>>> has no significance whatsoever.
>> 
>> Well, no…
> 
> Huh?  Are we talking about the same thing?  Which non-optional element
> of the FITS standard did I leave out?

You’ll note from the timestamp that it was 7am and before my first cup of coffee.  I was commenting on the assertion that “optional has no significance”.  I suppose you are suggesting that since pretty much everything is optional after the first 2880-byte record that we might omit the word optional for more particular cases throughout the standard?

> Ignoring INHERIT or CONTINUE potentially produces *wrong* answers
> without providing even a hint that anything is wrong.  That's not
> what I call "harmless".

In previous cases of modifying the standard we have jiggered things such that new-format files might either be invisible to unmodified software (e.g., relying on the extra appended record gimmick), or rather would cause unmodified software to abort (e.g., negative BITPIX values).

But several of the conventions are already perfectly legal FITS.  And projects already use INHERIT, for instance.  Improving the documentation and hooks for recognizing such usage will be surely "less harmful”, if not “harmless", right?

Rob