Dear Nan
> DEPTH:reference=<R>;
> where currently vetted values for R are "mean_sea_level",
> "mean_lower_low_water",
> "wgs84_geoid" and the default, "sea_level".
>
> DEPTH:coordinate_reference_frame="urn:ogc:crs:EPSG::5831"; or
> HEIGHT:coordinate_reference_frame="urn:ogc:crs:EPSG::5829";
> 5831 and 5829 can be resolved at http://www.epsg-registry.org/ but are not
> meant for human information. They're defined as 'depth (or height)
> relative to instantaneous
> water level, uncorrected for tide.'
The above is interesting. This and Rich's posting suggests that maybe part of
the difficulty is a different organisation of concepts in CF. Maybe this is
just my personal confusion, but I might not be the only one.
The standard_names of depth and height in CF are defined as meaning vertical
distance below and above "the surface". In stdnames, "the surface" means the
bottom of the atmosphere. So these concepts include a vertical datum. There is
no CF stdname for vertical distance above some surface to be specified in
another part of the metadata. All the stdnames which somehow involve a special
surface (like The Surface, the geoid, the tropopause, the top of the
atmosphere, the bedrock) identify it in the stdname itself.
However, some of these special surfaces might have to be more precisely
defined in extra metadata to accompany the standard name. This can already
be done for a reference ellipsoid, but not for a geoid.
Best wishes
Jonathan
Received on Thu Feb 06 2014 - 09:54:40 GMT
