[fitsbits] structurally compliant FITS

[Mark Calabretta]

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.  Implicit in your description is that a single FITS-
>compliant ASCII 2880-byte record was received.  Underneath all the
>semantics and data representation issues we are discussing is a very
>simple and solid framework of a sequence of structurally compliant
>HDUs.  Useful utilities (or archive components like NOAO's "Save the
>Bits") may well view a FITS file at only this most basic level.
>Sending such a simple file could serve a useful purpose as an
>"iamalive" packet, for instance.

Huh?  Are we talking about the same thing?  Which non-optional element
of the FITS standard did I leave out?

>>Ignoring INHERIT could lose you a stack of porentially important
>>keywords.  Ignoring CONTINUE could lose the nether end of string
>>keyvalues.  Ignoring tiled compression could render the image
>>unreadable.  How is that harmless?
> 
>I want to say that in an ideal world all FITS-compliant software would
>recognize all variations of FITS usage.  I want to, but I don't
>actually believe this.  On the one hand there is a layer beneath even
>the structural example given above.  Vast numbers of useful host level
>tools can be used with FITS files - tools that don't know nothin' about
>FITS.  And on the other hand is it really true that FITS "competitors"
>are any different?  Do all jpeg tools understand all JPEG2000 features?
>Is all the complexity of HDF5 supported in all its gory details
>wherever an HDF5 file may travel?  Surely we all can recount instances
>of MS Word-compliant files not being compatible with our version of
>Word or third-party software?

Dunno about HDF5, but JPEG2000-unaware software produces an error
message and no image at all.

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

Regards,
Mark