[CF-metadata] Coordinate System nomenclature in netcdf-java-2.2 / CDM:

[John Caron]

Brian Eaton wrote:

>On Wed, Dec 22, 2004 at 02:28:16PM -0500, Rich Signell wrote:
>  
>
>>This seems to be agreeing with Brian's earlier statement that saving 4D 
>>fields of Z are allowed already, enabled by the "coordinates" 
>>attribute.   Can one of you guys give an example of how this would be 
>>done?  I have only seen the "coordinates" attribute used to specify 
>>two-dimensional longitude and latitude fields.  
>>    
>>
>
>In general, the "coordinates" attribute is used to point to variables that
>contain coordinate information that can't be represented by a coordinate
>variable (note that the conventions always use the term coordinate variable
>to mean a 1D variable whose name matches the name of its dimension).  The
>only restriction on an auxiliary coordinate variable are that its
>dimensions are a subset (not necesarily proper) of the variable to which it
>is attached (and of course there's an exceptional case for dealing with
>label coordinates).  
>
FYI, we have started using the following nomenclature in the Coordinate 
System layer in netcdf-java -2.2 and the common data model:

A "coordinate variable alias" is really a coordinate variable (1D, 
monotonic) but its name doesnt match its dimension.

A "coordinate axis" is a generalization of a coordinate variable, it may 
have more than 1 dimension and may have any name. it acts like a 
coordinate variable in that it assignes a coordinate value to each value 
in a data variable. It is the same i think as CF's "auxiliary coordinate 
variable". A coordinate variable is also a coordinate axis.

A "coordinate system" for a data variable is a set of coordinate axes.

A "georeferencing coordinate system" for a data variable is a set of 
coordinate axes that give us lat, lon (or x, y on projection plane),  z, 
and time coordinates for each value in the data variable.