Dear Ethan, Balaji et al. No-one is suggesting having different standard names for different geoids or different reference ellipsoids, as far as I know. We agree that the identity of the geoid etc. belongs in the grid mapping. The distinction of standard names is for different geophysical quantities. The distinction of what is truly different is blurred, but we have to make black-and-white choices. The one which we make in many existing CF standard names is that if quantities refer to different geophysically defined surfaces that makes them different geo- physical quantities. I think that's a useful distinction for a data-analyst. Geoid, reference ellipsoid, surface (i.e. bottom of the atmosphere), bedrock (bottom of atmosphere, sea or ice sheet, whichever is lowest) and mean sea level are all different geophysical concepts, aren't they. In my opinion, primarily as a scientist analysing data, heights referring to these various references are not the same geophysical quantity, and I expect them to have different standard names. That is the approach we have followed in naming quantities up to now.
I agree with Balaji to the extent that the standard name is not a complete characterisation of a quantity. There is other CF metadata. Especially, there are coordinates. The height of cloud can be specified by coordinates, which avoids the needs for more standard names, is more precise and much more flexible. I regard cloud amount on any level as the same geophysical quantity (while acknowledging that different cloud microphysics is at work, of course) and so I am happy for clouds at various heights to be distinguished by coordinates. The same is the reason why we have a standard_name for air_temperature, but we don't have one for "surface air temperature", since the extra precision can be supplied by a coordinate of height. This is another blurred distinction, I realise, but I think it works quite well in practice. Cheers Jonathan ----- Forwarded message from Ethan Davis <eda...@unidata.ucar.edu> ----- > Date: Wed, 12 Feb 2014 10:43:46 -0700 > From: Ethan Davis <eda...@unidata.ucar.edu> > User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 > Thunderbird/24.3.0 > To: cf-metadata@cgd.ucar.edu > Subject: Re: [CF-metadata] Vertical datums (again) > > Hi all, > > I agree with Jim on this. The grid_mapping, rather than the standard > name, is the appropriate place for this information. Just as it is for > "latitude" and "longitude (and X and Y). We don't have "latitude-wgs84" > or "latitude-airy-1830". > > Ethan > > On 2/11/2014 11:51 AM, Jim Biard wrote: > > Karl, > > > > My point is that putting the reference surface in the standard name > > (potentially) proliferates standard names for things that (like > > temperatures in different units) are not different except for their > > reference frame. I agree that we don?t want to put the datum > > information in the units, but the place for this sort of information > > already exists - it?s the grid_mapping variable. We don?t have the > > appropriate attributes defined yet, but that is where the information > > should go. The definition of the standard name can state a requirement > > for the information to present in a grid_mapping variable. I thought > > that the point of standard names was to assist in identifying variables > > that are of the same kind or class, and that the goal was to avoid > > putting implementation details into standard_names. By tacking on CRS > > details, it seems to me that we are moving away from that goal. > > > > Grace and peace, > > > > Jim _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
