[CF-metadata] Monotonic coordinates

From: Jonathan Gregory <j.m.gregory>
Date: Thu, 20 Dec 2012 07:51:19 +0000

Dear Bill

Yes, I agree with you, the values of a CF coordinate variable (not an auxiliary
coordinate variable) must all be different, as the NUG says; CF generally
upholds the NUG. In principle this is because the coordinate variables are the
independent variables on which the data values depend. Independent variables
should be single-valued.

You could propose a CF trac defect ticket to modify the text of the CF
standard in order to clarify this.

Best wishes

Jonathan

> In CF Metadata Conventions section 1.2. Terminology, a coordinate
> variable "is defined as a numeric data type with values that are ordered
> monotonically."
>
> This suggests that weak-monotonicity is acceptable.
>
> Within the same section and paragraph, reference is made to section
> 2.3.1. of the NUG, which states that coordinate variables "are numeric
> vectors and strictly monotonic (all values are different and either
> increasing or decreasing)."
>
> This states that strict-monotonicity is required.
>
> The definition of a CF coordinate variable is fundamental to the CF
> model, and yet its specification from the wording in the conventions
> document is unclear.
>
> I feel that explicit clarification on this matter within the CF Metadata
> Conventions document is well overdue.
Received on Thu Dec 20 2012 - 00:51:19 GMT