[CF-metadata] Vertical datums (again)

From: Jonathan Gregory <j.m.gregory>
Date: Fri, 14 Mar 2014 18:21:03 +0000

Dear Jim

Given what you say, what would you suggest for the grid_mapping_name when the
grid_mapping supplies only the figure of the Earth and does not specify any
transformation of coordinate systems?

I agree that grid_mapping is itself an unsatisfactory name, which reflects
the purpose we had in mind when it was first introduced, subsequently
generalised. In the data model we can (and indeed we propose to) call it
something else. We could change its name in the convention but we'd have to
retain the old one too for backward compatibility, I'd argue, and I would
feel it's not worth the effort. It's more important to describe clearly what
it does in principle.

Best wishes and thanks

Jonathan


----- Forwarded message from Jim Biard <jbiard at cicsnc.org> -----

> The contents of the grid_mapping variable are doing as much mapping when specifying a projected coordinate system as they are when specifying a geographic (i.e., lon/lat) coordinate system. It is telling you how to understand the spatial coordinate information, particularly in relation to any other choice of coordinate system. It has an unfortunate name, in that it leads us to think about it as ?the thing that tells me how I got from my X & Y coordinate variables to my lon & lat grids?. When you have both X/Y coordinates and lon/lat auxiliary coordinates, the grid_mapping variable is actually telling you how to understand both. There is really no such thing as a ?null mapping?.
Received on Fri Mar 14 2014 - 12:21:03 GMT