[CF-metadata] CF compliant tripolar grid representation

Jim Biard jbiard at cicsnc.org
Fri Mar 31 10:04:25 MDT 2017


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,


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
> -- 
> David Hassell
> National Centre for Atmospheric Science
> Department of Meteorology, University of Reading,
> Earley Gate, PO Box 243, Reading RG6 6BB
> Tel: +4
> ​4 ​
> 118 378 5613
> http://www.met.reading.ac.uk/

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