[CF-metadata] Vertical datums (again)

From: Jonathan Gregory <j.m.gregory>
Date: Thu, 6 Feb 2014 16:47:26 +0000

Dear Rich

> Yes, I think your answer before is the answer now, but I'm just clear
> on the details. Would you specify sea_surface_height above NAVD88
> like this?
>
> float zeta(y=1534, x=2122);
> :standard_name = "sea_surface_height_above_reference_datum";
> :grid_mapping = "Albers_Projection";
>
> int Albers_Projection;
> :grid_mapping_name = "albers_conical_equal_area";
> :standard_parallel = 20.5, 27.5; // double
> :longitude_of_central_meridian = -89.0; // double
> :latitude_of_projection_origin = 24.0; // double
> :false_easting = 0.0; // double
> :false_north = 0.0; // double
> :vertical_datum = 'urn:ogc:def:datum:epsg::5103'

I'm not clear still what NAVD88 is though. SSH must be above some surface. Is
this surface a reference ellipsoid or a geoid? These are two different standard
names:
  sea_surface_height_above_geoid
  sea_surface_height_above_reference_ellipsoid
whereas sea_surface_height_above_reference_datum is not an existing stdname.

If it's a reference ellipsoid, it can be described already by grid_mapping
parameters. To name a geoid, we'd need a new attribute of grid_mapping, but
I don't think that would be problematic.

Best wishes

Jonathan
Received on Thu Feb 06 2014 - 09:47:26 GMT