Hello,
The CF Convention 1.6 and draft 1.7 both include, in the discussion of dimensions in Section 2.4, the statement that:
"It is also acceptable to use a scalar coordinate variable which eliminates the need for an associated size one dimension in the data variable."
However, the convention states that coordinate variables should be interpreted as 'NUG-defined "coordinate variables."'. The NUG is vague about the definition (
https://www.unidata.ucar.edu/software/netcdf/docs/coordinate_variables.html ), but it does say "Current application packages that make use of coordinate variables commonly assume they are numeric vectors and strictly monotonic". It also states that "A position along a dimension can be specified using an index", which is not consistent with the use of a scalar coordinate variable.
One application which appears to assume that coordinate variables are vectors is the CF Checker, so we need some clarification. I'm not sure how other applications deal with it.
The problem with the current phrasing in the CF Conventions document is that it suggests the NUG approach is being followed and then introduces a departure from the NUG approach in a separate part of the text.
I would recommend either adding after 'NUG-defined "coordinate variables"' a clarification '(that is a scalar or vector variable with the same name as a dimension)', or changing the statement about use of scalar coordinate variables.
regards,
Martin
Received on Tue Dec 08 2015 - 02:58:29 GMT
