[fitsbits] Repeated header keywords

[Peter Bunclark]

Dick Shaw wrote:

> 
> 
> One approach would be to say that headers _should not_ contain repeated 
> keywords, and if a repeat does occur then the value is not defined 
> (unless the values are identical). Ideally, this could have a few 
> desired effects: it would encourage authors of FITS verifiers to flag 
> instances of repeated keywords (though I suspect they do already), it 
> would encourage FITS writers to pay attention to this problem, and it 
> would encourage application developers to be refrain from silently 
> adopting the first, last, or whatever instance of a keyword value 
> without telling the user.

This looks to me like the best wording so far.  I too have had many a 
weary battle with ``software engineers'' to get them to to conform to 
the existing standard; expecting a change which in so many cases just 
doesn't matter (the example of duplicated instrument temperatures) will 
just get zero priority.

Would it be too complex to make the non-duplication of reserved words 
mandatory and of others just strongly recommended?

In the real world, if crucial keywords like those in the WCS are 
repeated with different values, and applications randomly choose one or 
the other, that should soon be seen as a hard bug in the FITS writer and 
would get fixed - although of course it would be better if verification 
software caught such problems first. But if the verification program 
marks all my data files as non-conforming because of a duplicate 
temperature reading, I get into the regime of "oh, you can ignore those 
errors, they're not important" (er, I also support the less-able end of 
the software community).  I really want to be able to say to the 
software authors "keep going till fitsverify passes".

Pete.