It's been suggested to me that it might help open up this discussion if I could post up a suggested text for scalar coordinate variables, which recognises their semantics within NetCDF files.
If there is some feeling that this is a helpful step, I will raise a trac ticket to discuss the finer points of detail on wording and implications and look to possible approval by the community.
These are suggested alterations to sections in the conventions text. I think all of the current examples (5.11, H4, H5 and H9) remain valid as they are. I think the conventions would benefit from further examples, I leave the discussion on which cases could be most useful to illustrate the usage and implications of scalar coordinates to a potential trac ticket.
mark
Scalar Coordinate Variables
1.2 Terminology
A scalar coordinate variable defines a single valued coordinate for a data variable which applies to the whole data variable equally.
5.7 Scalar Coordinate Variables
A scalar coordinate variables defines a data variable's coordinate with a single data value point. It is associated with a data variable via the coordinates attribute. The scalar coordinate variable must not share any dimensions with the data variable. A single bounds set may be defined for a scalar coordinate variable.
A scalar coordinate variable applies equally to the entire data variable, it does not vary with respect to the data variable's dimensions.
A scalar coordinate variable may be interpreted as implying a further degree of freedom for the data variable, not defined by the data variable's stated dimensions; such degrees of freedom are not explicitly defined.
The variable name of a scalar coordinate variable must not match the name of any dimension in the file.
Note that use of scalar coordinate variables for latitude, longitude, vertical, or time coordinates will inhibit COARDS conforming applications from recognizing them.
6.1 Labels
... {Unchanged, up to the last sentence}
If a character variable has only one dimension (the maximum length of the string), it is a string-valued scalar coordinate variable (see Section 5.7 Scalar Coordinate Variables).
9.2 Collections, Instances and Elements
... {First two paragraphs unchanged}
If there is only a single feature to be stored in a data variable, the instance dimension may be omitted. In this case coordinate variables will not vary with respect to the instance dimension. Mandatory space-time coordinates in table 9.1 may need to be defined as scalar coordinate variables, to maintain the required relationships for the feature types.
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Received on Wed Jun 12 2013 - 03:33:17 BST
