Hello Martin, This definition was tightened up in ticket #104 <https://cf-trac.llnl.gov/trac/ticket/104>. An arbitrary scalar coordinate can be either, but not both at the same time. At version 1.7, section 5.7 ( http://cfconventions.org/cf-conventions/cf-conventions.html#scalar-coordinate-variables) now says:
"A numeric scalar coordinate variable has the same information content and can be used in the same contexts as a size one numeric coordinate variable. Similarly, a string-valued scalar coordinate variable has the same meaning and purposes as a size one string-valued auxiliary coordinate variable" Thanks, David On 30 July 2017 at 07:50, <[email protected]> wrote: > Dear All, > > I'm afraid I'm not undrestanding how you are distinguishing between > "auxillary" and other coordinates. The terminology section of the CF > Convention says that a variable is an auxillary coordinate if it contains > coordinate data and is not an NUG coordinate. The definition of a scalar > coordinate states that a scalar coordinate can be either an auxillary > coordinate or a coordinate variable .. so the "height" variable here is > both a scalar coordinate and an auxillary coordinate. It is clearly not a > NUG coordinate variable. > > > regards, > Martin > > ------------------------------------------------------------ > ---------------------------------------------------------------- > > David, > > I'm still not convinced of the utility of axis for coordinate variables > that aren't true coordinate variables, but this case doesn't fit that > one, does it? In this case isn't height a true (scalar) coordinate > variable? Shouldn't this pass the checker, regardless? > > Jim > > > On 5/24/17 3:54 PM, David Hassell wrote: > > Hi Jim, Martin, > > > > I agree - "height" in this case is not an auxiliary coordinate > > variable, rather a scalar coordinate variable (because it doesn't span > > any of the dimensions of "tas"). > > > > I also agree that the conformance document needs changing to allow the > > "axis" attribute on auxiliary coordinate variables - this was accepted > > in CF-1.6, I think. > > > > Thanks, > > > > Daivd > > > > > > > > On 24 May 2017 at 19:59, Jim Biard <jbiard at cicsnc.org > > <mailto:jbiard at cicsnc.org>> wrote: > > > > Martin, > > > > We just had some discussion about the proper use of the axis > > attribute, but this seems to me like it might be a flaw in the > > checker. As a scalar coordinate, height can only be associated > > with the tas variable via the coordinates attribute (per section > > 5.7), but I don't think that makes it an auxiliary coordinate, > > does it? > > > > What do other people think? Chime in! > > > > Grace and peace, > > > > Jim > > > > > > On 5/23/17 10:50 AM, martin.juckes at stfc.ac.uk > > <mailto:martin.juckes at stfc.ac.uk> wrote: > >> Hello All, > >> > >> I'd just like to check one aspect of the conformanc document, which > came to our attention when somebody ran the CF checker on some CMIP5. If > you check using the convention version declared in the file, 1.4, it will > raise an error if there is a scalar coordinate variable with the axis > attribute set, e.g. > >> > >> float tas(time,lat,lon); > >> ...... > >> tas:coordinates = "height" ; > >> float height ; > >> .... > >> height: axis = "Z"; > >> > >> In this case "height" variable is, following the logic of section > 1.2 of the convention, classed as an auxillary coordinate because it is not > of the form "height (height) ; ". > >> > >> The error message appears to relate to a line in the conformance > document saying that "The axis attribute is not allowed for auxiliary > coordinate variables." If the checker is asked to use a later version of > the convention, the error message goes away, but the requirement is still > there in the conformance document. > >> > >> It looks to me as though it should be removed from the conformance > document. The convention document says, in section 4. that "The methods of > identifying coordinate types described in this section apply both to > coordinate variables", referring to the use of the axis attribute, which > appears to directly contradict the line of the conformance document cited > above. But is there another part of the convention that requires some > restriction on the use of the axis attribute? > >> > >> This construction is widely used in CMIP data, so we should get > this point cleared up. > >> > >> regards, > >> Martin > >> > >> _______________________________________________ > >> CF-metadata mailing list > >> CF-metadata at cgd.ucar.edu <mailto:CF-metadata at cgd.ucar.edu> > >> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > >> <http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata> > > -- > > CICS-NC <http://www.cicsnc.org/> Visit us on Facebook > > <http://www.facebook.com/cicsnc> *Jim Biard* *Research Scholar* > > Cooperative Institute for Climate and Satellites NC > > <http://cicsnc.org/> North Carolina State University > > <http://ncsu.edu/> NOAA National Centers for Environmental > > Information <http://ncdc.noaa.gov/> /formerly NOAA’s National > > Climatic Data Center/ 151 Patton Ave, Asheville, NC 28801 e: > > jbiard at cicsnc.org <mailto:jbiard at cicsnc.org> o: +1 828 271 > 4900 > > <tel:%28828%29%20271-4900> /Connect with us on Facebook for > > climate <https://www.facebook.com/NOAANCEIclimate> and ocean and > > geophysics <https://www.facebook.com/NOAANCEIoceangeo> > > information, and follow us on Twitter at @NOAANCEIclimate > > <https://twitter.com/NOAANCEIclimate> and @NOAANCEIocngeo > > <https://twitter.com/NOAANCEIocngeo>. / > > > > _______________________________________________ CF-metadata > > mailing list CF-metadata at cgd.ucar.edu > > <mailto:CF-metadata at cgd.ucar.edu> > > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > > <http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata> > > > > -- > > David HassellNational Centre for Atmospheric ScienceDepartment of > > Meteorology, University of Reading, Earley Gate, PO Box 243, Reading > > RG6 6BB Tel: +44 118 378 5613http://www.met.reading.ac.uk/ > -- > CICS-NC <http://www.cicsnc.org/> Visit us on Facebook > <http://www.facebook.com/cicsnc> *Jim Biard* *Research Scholar* > Cooperative Institute for Climate and Satellites NC <http://cicsnc.org/> > North Carolina State University <http://ncsu.edu/> NOAA National Centers > for Environmental Information <http://ncdc.noaa.gov/> /formerly NOAA’s > National Climatic Data Center/ 151 Patton Ave, Asheville, NC 28801 e: > jbiard at cicsnc.org <mailto:jbiard at cicsnc.org> o: +1 828 271 4900 > /Connect > with us on Facebook for climate > <https://www.facebook.com/NOAANCEIclimate> and ocean and geophysics > <https://www.facebook.com/NOAANCEIoceangeo> information, and follow us > on Twitter at @NOAANCEIclimate <https://twitter.com/NOAANCEIclimate> and > @NOAANCEIocngeo <https://twitter.com/NOAANCEIocngeo>. / > _______________________________________________ > CF-metadata mailing list > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > -- David Hassell National Centre for Atmospheric Science Department of Meteorology, University of Reading, Earley Gate, PO Box 243, Reading RG6 6BB Tel: +44 118 378 5613 http://www.met.reading.ac.uk/
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