Dear Paul, Etienne et al. > From my perspective I treat an EPSG code as a unit definition (in this > case a coordinate) as I would treat 'metres' as a unit definition for > length. CF conventions do not require the description of what a metre > implies; that is assumed knowledge, and I believe the EPSG code should > be treated likewise. If we make it easy to define the CRS, we will see > far more users actually specify one!
I see the analogy, but it's not a perfect one, because units are a much simpler business. There is only a handful of basic units, and the translations of all the derived units are easily accessible, well-known and completely dependable. In particular, there is readily available software for parsing and converting units. So, while I agree with your order of preference > Option 1: Long form : full parameter attribution (as per your ticket) > Option 2: Short form : EPSG code > Option 3: Compatibility form : wkt representation I think that Option 1 is much better than Option 2. Option 2 would be worth considering if there was a online service, or a machine-readable file available from a public repository, that CF software could use to translate EPSG codes into and out of parameters that could be equivalenced to CF grid_mapping attributes. As far as I understand (but I'm ready to be corrected) this is not the case. If it were the case, it would be possible to check automatically that the EPSG code and the grid_mapping in a CF file were consistent. Without such a check, I think it is dangerous to allow codes, because it is inevitable that some people will put codes in files without making sure that the grid_mapping is consistent with the code, and then data-analysts will get different results according to what information their software uses. This would obviously be a failure of the purpose of CF to "define metadata that provides a definitive description of ... the spatial and temporal properties of the data." Best wishes Jonathan _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
