Dear David Thanks for noticing the incorrect standard_name in Example 7.3. It looks like a defect to me too.
When Sect 7.2 was written, as far as I remember we had only horizontal area in mind. As you say, the convention doesn't exclude areas which are functions of non-horizontal axes, but that probably wasn't intended. So I think the answer is that the situation is ambiguous, and it should be clarified by explicitly allowing or disallowing non-horizontal areas as an "area" cell measure. If they are not allowed, but you have use-case where they are needed, a differently named measure should be proposed. I think that these would be substantive changes to the convention either way, not defects. The same applies to the standard_name. Either cell_area could have its definition generalised, or a new standard_name could be added. Best wishes Jonathan ----- Forwarded message from David Hassell <[email protected]> ----- > Date: Wed, 7 Oct 2015 16:37:48 +0100 > From: David Hassell <[email protected]> > To: [email protected] > Subject: [CF-metadata] cell measures for non-horizontal planes > User-Agent: Mutt/1.5.21 (2010-09-15) > > Hello, > > I was wondering if anyone can help clear something up for me: Can an > "area" cell measure variable span non-horizontal axes? For example, > could you have an area cell measure for X-Z cells? And if so, what > could its standard name be? E.g. > > float cell_area(longitude, height): > cell_area:measure = "area"; > cell_area:units = "m2"; > cell_area:standard_name = ????????????? > > I know that the standard_name attribute is optional, thus the two part > question. > > There is a standard name "cell_area" (= the horizontal area of a > gridcell), but not one for areas of arbitrarily orientated planes. > > The conventions (section 7.2) do not explicitly disallow > non-horizontal planes (that's three negatives in half a sentence!), > but if they're allowed then the assumption is, I think, that the plane > of the area is implied by the variable's dimensions and there is no > applicable standard name. This is tricky if the cell measure variable > does have X and Y dimensions, as in example 7.3. This example uses the > standard name "area" for its cell measure variable, but this name is > not in the table - I presume that "cell_area" is meant. I'll raise a > defect ticket for this if required. > > Many thanks and all the best, > > David > > -- > David Hassell > National Centre for Atmospheric Science (NCAS) > Department of Meteorology, University of Reading, > Earley Gate, PO Box 243, > Reading RG6 6BB, U.K. > > Tel : +44 118 3785613 > E-mail: [email protected] > _______________________________________________ > 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
