[CF-metadata] bounds not allowed for scalar coordinate variables

From: Jonathan Gregory <j.m.gregory>
Date: Thu, 16 Dec 2010 14:52:07 +0000

Dear Karl

> Does anyone remember, why we didn't allow the "bounds" attribute to be
> attached to a scalar coordinate variable? Currently CF requires the
> user to include a dimension a size one if he wants to define coordinate
> bounds:
>
> "The advantage of using a coordinate variable is that all its attributes
> can be used to describe the single-valued quantity, including boundaries."

I don't think the text means that a scalar coord var can't have bounds. In
the sentence you quote, it is not contrasting a (Unidata) coord var with a
scalar coord var. I believe that by "coordinate variable" it means either
a size-one (Unidata) coord var or a scalar coord var. It is contrasting the
use of coordinate vars of either type with attributes, as means of attaching
single values, I guess. Indeed, in 5.7, it says "Scalar coordinate variables
have the same information content and can be used in the same contexts as a
size one coordinate variable."

I often attach bounds to scalar coord vars and I don't believe the conformance
requirements exclude that.

> [Note that we also, don't allow an "axis" attribute to be attached to a
> scalar coordinate variable, and I also don't remember why we did this.]

Where do you find that? It is possible that this would be excluded because
scalar coord vars are (formally) auxiliary coord vars, which are specifically
excluded from having the axis attribute in the intro to 5. There were good
reasons for that but we ought to be revisit it. Steve Hankin has raised that.
I think scalar coord vars should be allowed to have the axis attr. That is
necessary if they are to have the same info content etc., as quoted above.

Best wishes

Jonathan
Received on Thu Dec 16 2010 - 07:52:07 GMT