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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