[fitsbits] Fwd: multiple keyword occurance in header

[Rob Seaman]

Meant to send this to fitsbits:

Begin forwarded message:

> From: Rob Seaman <seaman at noao.edu>
> Date: August 20, 2007 8:50:12 AM MST
> To: Walter Jaffe <jaffe at strw.leidenuniv.nl>
> Subject: Re: [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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