David,
As I read the Conventions, the axis attribute is to be applied to
coordinate variables (Section 4. Coordinate Types and Section 5.
Coordinate systems) to indicate that this variable can be treated as
representing an dimensional axis of corresponding variable grids.
Section 5 paragraph 6 talks about how it is still possible to figure out
that an auxiliary coordinate variable is a spatiotemporal dimension of
the if the axis attribute is not present. I don't think a 2D auxiliary
coordinate variable can be considered to be a dimensional axis, can it?
Grace and peace,
Jim
On 3/31/17 11:52 AM, David Hassell wrote:
Hello Sébastien and Jim,
You are right to feel weird about identifying 2D lat and lon as Y
and X axes. The axis attribute should never be applied to 2D
variables. It is only valid for 1D "true" coordinate variables.
The axis attribute can be attached to auxiliary coordinate variables
with any number of dimensions. I would agree, though, that attaching
the axis=X attribute to a 2-d longitude auxiliary coordinate variable
is likely to confuse. The axis attribute's purpose is merely to make
identification easier, but as long there are units of degrees_east
(mandatory) and a standard name of longitude (optional), humans and
software alike should be happy.
All the best,
David
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National Centre for Atmospheric Science
Department of Meteorology, University of Reading,
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Tel: +4
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http://www.met.reading.ac.uk/
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