sorry, didn't mean to send this to Bill (Pence) only.

Maren Purves wrote:
Bill,

I read this like Bill Thompson. The fact that the standard requires
EXTEND=T if there may be extensions doesn't prohibit putting EXTEND=F
(never mind the formatting) if there may (must) not be.

Of course if one wants to ignore either and read the whole file
either way that's up to the software used (but that's a very inclusive
way of seeing this).

?

Maren

William Pence wrote:
The difference here is that I was quoting the revised definition in
the new draft standard, which doesn't allow for the possibility that
EXTEND = F. Given that there are existing FITS files with EXTEND = F,
the definition should probably be revised to at least not prohibit
this usage.


William Thompson wrote:
It's not clear to me that the FITS standard forbids setting EXTEND=F.

EXTEND Keyword The use of extensions necessitates a single
additional keyword in the
primary header of the FITS file. If the FITS file may contain
extensions, a card image
with the keyword EXTEND and the value field containing the logical
value T must appear
in the primary header immediately after the last NAXISn card image,
or, if NAXIS=0,
the NAXIS card image. The presence of this keyword with the value T
in the primary
header does not require that extensions be present.
To me, having EXTEND=F when one knows that no extensions are present
is one of those "bedrock of logic" that Rob Seaman refers to.

Bill Thompson


William Pence wrote:
William Thompson wrote:

The SECCHI instrument on the STEREO mission produces some files
with table extensions, and other files which don't. The value of
the EXTEND keyword is set to either T or F to account for this.
Strictly speaking, this does not conform to the definition of the
EXTEND keyword in the FITS Standard, which states that the value
field *shall* contain a logical constant with the value T, and thus
must never be set to F. All the more reason I think to demote
this keyword by making it optional instead of required if the file
contains extensions.

Bill Pence