Hi Jonathan et al,
> (2) Precision about *which* real-Earth reference ellipsoid or geoid is meant.
> As others have said, this is related to the definition of the horizontal
> coordinate reference system. It has been raised several times before, and we
> deferred it from the discussion of Phil Bentley's ticket in order to limit the
> scope of the discussion and because it appeared no-one had time to formulate
> and describe a proposal to deal with the vertical aspects of the datum.
A significant CF governance/evolution issue here - one that I ran up
hard against when formulating trac proposals #9 and #18 - is that, in
attempting to put forward a proposal to address CF requirements A, B,
and C, one anticipates closely allied *future* requirements X, Y, and Z.
Yet the current CF 'philosophy', as I understand it, is to avoid
introducing new features until there is an identified and immediate need
for them.
This situation is especially pertinent to the complex realm of
coordinate reference systems, where it is difficult to focus on one
particular facet - vertical coordinate systems, say - without also
having to consider other facets - horizontal coordinate systems,
geodetic datums, ellipsoids, projections, and so on. It's an all-or-
nothing kind of problem domain.
This conflict between wanting to make manageable, incremental progress
[on the CF conventions] and wanting to put forward holistic solutions
that address a range of current and anticipated requirements, has IMHO
yet to be resolved. Personally I would like to see the latter approach
trialled, if nothing else, by implementing some of the larger-scale
changes (CRSs, common concept bundles, namespace support, etc) into a CF
2.0 candidate release. Existing CF-compliant software can then continue
to work against the CF 1.x specifications.
> this. The geoid model is too complicated to be specified by CF metadata, so I
> think it would have to be named in some way.
Ah, I see, so netCDF files don't always have to be self-describing
then :-))
Regards,
Phil
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