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[fitsbits] The CONTINUE and HIERARCH Conventions Public CommentPeriods



 
 
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Old September 10th 07, 10:29 PM posted to sci.astro.fits
William Pence
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Default [fitsbits] The CONTINUE and HIERARCH Conventions Public CommentPeriods

Rob Seaman wrote:
If we really want to extend FITS to allow longer
keyword names, then I think a much simpler way to do this is to just
allow free-format keyword records in which the "=" can appear anywhere
after byte 9 of the record, such as:

MY_LONG_KEYWORD = 17 / comment string


Bleh! No, no, no. Talk about needing to version FITS...


Why would versioning be necessary if this were to be adopted (not that
this is being seriously proposed)? I would think that adding a version
keyword to the new FITS files would only be necessary if there were
existing FITS files that would be invalidated, or potentially
misinterpreted, if read using the new free-format keyword parsing rules.

Note that this keyword is perfectly legal under the current FITS
Standard: existing FITS readers should interpret this as a
commentary-type keyword, with the 8-character name "MY_LONG_"
and the rest of the record treated as a comment string.


I don't think we've ever tested this in anger. A lot of FITS
applications likely still assume that the only commentary keywords
are COMMENT, HISTORY and BLANK.


Hopefully the FITS Standard is clear that if a keyword does not have a
"= " value indicator in bytes 9 and 10 of the record, then the keyword
does not have a formal value. The new wording in section 4.1.2.3 of the
proposed new FITS Standard is:

"In keyword records without a value indicator, bytes 9 through 80 should
be interpreted as commentary text, however, this does not preclude
conventions that interpret the contents of these bytes in other ways".

The HIERARCH and CONTINUE keyword conventions are examples of this.

As an important reminder, this proposed change in the wording of the
FITS Standard, along with hundreds of other changes, are all available
for review and public comment at
http://fits.gsfc.nasa.gov/fits_draft.html until the end of this month
(September).

I would like to strongly encourage members of the FITS community to
carefully read the entire new proposed Standard, and not just the short
summary documents that the technical panel prepared, to double check
that all of the proposed changes are clear and that they do not
inadvertently introduce undesirable changes or ambiguities.

Bill Pence
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__________________________________________________ __________________
Dr. William Pence
NASA/GSFC Code 662 HEASARC +1-301-286-4599 (voice)
Greenbelt MD 20771 +1-301-286-1684 (fax)


 




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[fitsbits] The CONTINUE and HIERARCH Conventions Public CommentPeriods William Pence FITS 4 September 21st 07 08:12 AM
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