[fitsbits] Proposed Changes to the FITS Standard

[William Thompson]

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

-- 
William Thompson
NASA Goddard Space Flight Center
Code 671
Greenbelt, MD  20771
USA

301-286-2040
William.T.Thompson.1 at gsfc.nasa.gov