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[CF-metadata] support for multiple auxulary coordinate variables

From: Jonathan Gregory <j.m.gregory>
Date: Wed, 5 Sep 2012 18:28:28 +0100

Dear Randy

I agree with what you write. You could list the alternative sets of three
coordinates each all as auxiliary coord vars, and distinguish them with
standard_names; presumably you would want to propose some new standard_names.
That would be fine and quite simple to do.

In addition, you could propose new grid_mappings. Up to now grid_mappings
have been for 2D coordinate systems, but you would want something in 3D,
I think. If it's likely generally useful, it would interesting to see a
proposal of what it might look like.

There is already an agreed change to the CF standard to allow more than
one grid_mapping for a given data variable. This was proposed by Mark Hedley
in ticket 70 https://cf-pcmdi.llnl.gov/trac/ticket/70 and will go in CF 1.7.

In response to Jim's comment, I would say that the data variable does have a
coordinate system; it's defined by the various coordinate variables that the
data variable is associated with, either 1D (Unidata) coordinate variables
or auxiliary coordinate variables. The role of the grid_mapping is to make
explicit the relationship among the coordinate variables of the space in which
the data variable exists.

Best wishes

Jonathan
Received on Wed Sep 05 2012 - 11:28:28 BST

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