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 <[email protected]> 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 > _______________________________________________ > CF-metadata mailing list > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
