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Thanks Russ and Ed,I had thought of doing something along these lines but I must say, Russ, your example makes it much simpler than I was thinking it would be. Thank-you.
Is something like this likely to be 'officially' sanctioned as a NUG recommendation at some stage?
regards Simon Wood Russ Rew wrote:
Hi Simon, You asked:Has anybody else been thinking about metadata for compound types? How is metadata expected to be represented for individual fields?and Ed Hartnett wrote:We have also considered that one could create an attribute of compound type, in which each element was a unit for an element of the data compound type.Just to expand on this a bit, I think this is an adequate way to provide attributes to members of a compound type, because attributes in netCDF-4 can be of user-defined types, not just of primitive types. As an example, consider a user-defined compound type "obs_type" and a 1D variable "obs_var" of that type: types: compound obs_type { // a user-defined compound type int station_id; double time; float temperature; float pressure; }; variables: obs_type obs_var(n); // a 1D variable of type obs_type To assign units to all the members of the obs_var variable (and any other variables of that type), just define a related type named "obs_atts", for example, and declare a variable attribute "units" of that type for the obs_var variable:types: ...compound obs_atts { // a user-defined compound type string station_id; string time; string temperature; string pressure; } variables: ... obs_atts obs_var:units = { // a units attribute of type obs_atts time = "hours since 2000-01-01 00:00"; temperature = "degreesC"; pressure = "hPa"; }; Notice that since the station_id member of the obs_type has no units, we do not include a station_id member in the associated obs_var:units attribute. Strictly speaking, there's no need to even use the same order for the members in the obs_atts type, since an association can be made by using the same member names. Also if you wanted to associate a "standard_name" attribute string with each member of the obs_type, you would need to define another variable attribute named "standard_name" for the obs_var variable, but you wouldn't need another type: variables: ... obs_atts obs_var:standard_name = { // another attribute of type obs_atts temperature = "air_temperature"; pressure = "air_pressure"; }; There is a convention implicit in the above, that identity of member names between attribute compound types and variable compound types can be used to associate attributes with members of compound types, but I think this convention is natural and easy to understand. --Russ _____________________________________________________________________ Russ Rew UCAR Unidata Program russ@xxxxxxxxxxxxxxxx http://www.unidata.ucar.edu ============================================================================== To unsubscribe netcdf-hdf, visit: http://www.unidata.ucar.edu/mailing-list-delete-form.html ==============================================================================
-- Simon Wood Meteorology & Remote Sensing Scientific Programmer NIWA simon.wood@xxxxxxxxxx http://www.niwa.co.nz ============================================================================== To unsubscribe netcdf-hdf, visit: http://www.unidata.ucar.edu/mailing-list-delete-form.html ==============================================================================
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