Hi Jonathan,
>
> Also, existing authorities will only cater for commonly used CRSs. To have the
> flexibility to use any CRS, you need a way to describe it. More specifically,
> existing authorities are only interested in the real world, whereas our files
> have to deal with various model worlds as well.
Au contraire! The EPSG/OGP geodetic database includes hundreds (possibly
thousands) of obscure CRS definitions, many of them seemingly so
parochial I can't even begin to imagine how or where they are used!
Happily the EPSG database is driven by the oil & gas industry so it has
a) substantial resourcing; b) some very smart people contributing to
it :-) (Though admittedly it does focus primarily on traditional 2D and
2D + 1D-vertical coordinate systems.)
>
> To some extent I am being devil's advocate here, but I would like to know what
> extra information you get about the CRS if you look up the URN than we are
> anyway proposing to store in netCDF attributes.
You'd find a whole load of extra CRS information, much of it esoteric
and the preserve of specialist geodetic / surveying / mapping
applications. Far too much to even begin describing here.
The key benefit, I believe, in moving towards the URN-type approach -
and this reiterates the point made by Bryan in his reply - is that you
are referencing a single source of information truth. I should have
thought there was a far greater chance of inconsistency (i.e. typing
errors) arising from data producers having to specify several CRS
attributes for each and every netCDF file they create.
Regards,
--Phil
PS: the notion of URNs for CF names - our very own controlled
vocabulary! - would definitely be a boon. And I see there is a related
discussion in Trac ticket 11 (
http://cf-pcmdi.llnl.gov/trac/ticket/11).
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