Dear Thomas and Tom The simple method proposed by Thomas in ticket 79 still looks good to me. I would note that, since the earlier discussion, status_flag has been introduced as a standard_name (as well as a modifier) - that was one of the motivations of the proposal original.
Best wishes Jonathan ----- Forwarded message from "Clune, Thomas L. (GSFC-6101)" <[email protected]> ----- > Date: Thu, 27 Oct 2016 20:19:30 +0000 > From: "Clune, Thomas L. (GSFC-6101)" <[email protected]> > To: Thomas Lavergne <[email protected]> > CC: "[email protected]" <[email protected]>, "Auer, Benjamin M. > (GSFC-610.1)[SCIENCE SYSTEMS AND APPLICATIONS INC]" > <[email protected]>, "Trayanov, Atanas L. (GSFC-610.1)[SCIENCE > SYSTEMS AND APPLICATIONS INC]" <[email protected]> > Subject: Re: [CF-metadata] annotating vector quantities (e.g., (u,v) winds) > > Hello Thomas, > > Thank you very much for pointing me at the previous discussion. (And > apologies for not having done the search for myself.) > > I’m not sure I understand one sentence in the proposal: > > "To be valid, a vector variable shall have at least as many components > as the dimensionality of the vector.” > > I do not see where the proposal defines the “dimensionality” of the vector, > aside from the number of components. Hopefully this is not the number of > coordinate dimensions, as it does not suit our current needs. > > Consider (u,v) in a climate model using a lat lon grid. Here u and v are > both 3 dimensional (level, lat, lon). Yes, in theory there is a “w” > component out there somewhere, but in practice it is treated quite > differently. And, even in the document, the variables do have a time > dimension that would seem to run afoul of this constraint. And finally, > consider our new situation where the data is to be exported on cubed-sphere > grid. In this case, our variables have dims: (time, level, nf, ny, nx), > where “nf” is 6 corresponding to the 6 faces of the cube. But our wind is > still 2D - there is no “face” component of the wind. > > Aside from that concern, I think the proposal meets our needs. > > Cheers, > > - Tom > > > > On Oct 27, 2016, at 3:51 PM, Thomas Lavergne > <[email protected]<mailto:[email protected]>> wrote: > > Dear Thomas, and colleagues, > > Thank you for bringing this topic back in the spot lights. I made an attempt > to define vectors in CF about 4 years ago. There was a lot of good discussion > in here (http://cf-trac.llnl.gov/trac/ticket/79) but we unfortunately never > reached a conclusion (although there was some level of consensus at the > start). I will gladely participate to this discussion. > > T. > > 2016-10-27 21:23 GMT+02:00 Clune, Thomas L. (GSFC-6101) > <[email protected]<mailto:[email protected]>>: > I could not find any discussion in the specs about how to indicate that two > variables are part of a vector pair such as (u,v). In theory one can infer > the relationship from the long-name, but it would seem to be useful to have a > more direct means to indicate this relationship. > > I see at least 4 different approaches to this: > > > 1. Each variable that is part of a vector has an attribute that names the > partner component. u:vector_partner = “v" There is also an attribute that > specifies the component index: u:vector_index=1 Others may want vectors > with more components, in which case naming the partners becomes more > problematic. And then one would also want an attribute that specifies the > total number of components u:vector_length=2 > 2. Each vector component has an attribute that names the entire vector > rather than the partner. u:vector_name=“u-v”. There would also be an > attribute for specifying the vector component index as in (1) above. This > approach is more scalable for longer vectors, but tools would need to search > through all variables to find the partner components. > 3. Have a separate variable which is a vector of strings. Each string > names the list of component variables with some standard separator. E.g., > “u,v”, “mx, my”, … > 4. Combine components into one variable with an extra vector index > dimension. But this seems to be contrary to CF conventions for naming > variables. It is also not very friendly to the tools that we are currently > using. > > Thanks in advance, > > - Tom > > > _______________________________________________ > CF-metadata mailing list > [email protected]<mailto:[email protected]> > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > > > > > -- > ========================================== > Thomas Lavergne > Norwegian Meteorological Institute > P.O.BOX 43, Blindern, NO-0313 OSLO, Norway > Phone: (+47) 22963364<callto:+47%29%2022963364> Skype: > thomas.lavergne<callto:+47%29%2022963380> > Email: [email protected]<mailto:[email protected]> > OSISAF HL Portal: http://osisaf.met.no<http://osisaf.met.no/> > ========================================== > > _______________________________________________ > CF-metadata mailing list > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata ----- End forwarded message ----- _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
