As I recall, disallowing missing data for auxiliary coordinate variables was originally just 'inherited' from the rule for coordinate variables. The argument was made (correctly I think) that sometimes the auxiliary coordinate variable is measured or calculated as part of the same process that generates the data which *has* the auxiliary coordinate variable, and that it didn't make sense to force the generation of auxiliary coordinate variables in those cases.
I think this argument was made and accepted by all a little while back, and I've seen nothing refuting it.
John
On Feb 21, 2014, at 14:35, Jonathan Gregory <j.m.gregory at reading.ac.uk> wrote:
> Dear Jim
>
>> For Rich?s case it may be that the complex grid network is stretched out somehow into a rectangular array space, so there are no coordinates to have for the ?missing? elements.
>
> But that seem to imply there are no (non-auxiliary) coordinates either. Perhaps
> that was the case. I've forgotten. Is that right, Rich?
>
>> As to whether or not missing values have ever actually been forbidden in auxiliary coordinates (except in people?s minds), here?s the definition from the CF conventions document.
>
> Yes, aux coord vars are not coord vars, but they contain coordinate data.
> Table A indicates vars which indicates coord data with C. _FillValue and
> missing_value did not have C until it was added for the sake of chapter 9.
> I am certain we intentionally did not previously allow aux coord vars to
> include missing data.
>
> What I am wondering is if anyone can recall or think of something which would
> go wrong if we allowed this. Obviously one thing that probably would go wrong
> is that existing software, not expecting to check for missing data in aux
> coord vars, would wrongly interpret missing data if it was actually included.
> If a change would break existing software, there has to be a good reason for
> making the change.
>
> Cheers
>
> Jonathan
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Received on Fri Feb 21 2014 - 16:41:21 GMT
