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[fitsbits] Fwd: multiple keyword occurance in header



 
 
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Old August 20th 07, 04:50 PM posted to sci.astro.fits
Rob Seaman
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Default [fitsbits] Fwd: multiple keyword occurance in header

Meant to send this to fitsbits:

Begin forwarded message:

From: Rob Seaman
Date: August 20, 2007 8:50:12 AM MST
To: Walter Jaffe
Subject: [fitsbits] multiple keyword occurance in header

On Aug 20, 2007, at 7:58 AM, Walter Jaffe wrote:

Such occurances probably occur mostly when histories of
previous reduction steps are copied into the headers
of downstream products. Originally this kind of
information was supposed to be recorded with
HISTORY keywords, but I can imagine that many
programmers ignore this option because it requires
reformatting each card image. Maybe something like
BLOCK HISTORY BEGIN
... literal copy of keywords from previous steps ...
BLOCK HISTORY END


Well, it's a good thought that we might want to understand why
issues like duplicate keywords occur before making changes to the
standard. But I'm not sure I see the advantage of:

BLOCK HISTORY BEGIN
text 1
text 2
text 3
BLOCK HISTORY END

to

HISTORY text 1
HISTORY text 2
HISTORY text 3

other than gaining 8 characters per line.

In any event, sequential header edits is only one way duplicates
can arise. NOAO iSTB grabs raw data from a couple of dozen
different instruments. These raw data often demonstrate a wide
variety of "interesting" metadata, with just one example being
duplicate keywords. I would attribute this to an interaction
between various groups (who often work for different
organizations): the instrument engineers, the data acquisition
programmers, the telescope control system, the data handling system
- to name a few. There often is no one final arbiter of the
content of the header - and this issue is rarely at the top of the
list for anybody before the data reach the archivists. In fact, an
archive is an instrumentality for asserting coherent standards -
but it requires a bit more subtlety than simply telling everybody
up stream that something is verboten.

Rob



 




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