Hi Philip,
> 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 is a very good point - in fact ISO 19111 says that you can't
separate horizontal and vertical CRSs in some cases. I'm wary of
making such proposals myself because I frankly don't understand all
the issues properly (we need some geodesists or GIS experts or
something). So it's a tricky one.
Cheers, Jon
On Thu, Aug 7, 2008 at 5:48 PM, Philip Bentley
<philip.bentley at metoffice.gov.uk> wrote:
> 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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Technical Director Tel: +44 118 378 8741 (ESSC)
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Received on Thu Aug 07 2008 - 14:27:54 BST
