Hi Martin, The terminology entry has also been updated:
auxiliary coordinate variable Any netCDF variable that contains coordinate data, but is not a coordinate variable (in the sense of that term defined by the NUG and used by this standard - see below). Unlike coordinate variables, there is no relationship between the name of an auxiliary coordinate variable and the name(s) of its dimension(s). scalar coordinate variable A scalar variable (i.e. one with no dimensions) that contains coordinate data. Depending on context, it may be functionally equivalent either to a size-one coordinate variable (Section 5.7, "Scalar Coordinate Variables" <http://cfconventions.org/cf-conventions/cf-conventions.html#scalar-coordinate-variables>) or to a size-one auxiliary coordinate variable (Section 6.1, "Labels" <http://cfconventions.org/cf-conventions/cf-conventions.html#labels> and Section 9.2, "Collections, instances, and elements" <http://cfconventions.org/cf-conventions/cf-conventions.html#collections-instances-elements> ). The phrase "and used by this standard" allows, I think, the scalar coordinate variable to not be an auxiliary coordinate in the right context (i.e. when it's numeric). Does that make sense? Thanks, David On 31 July 2017 at 09:55, <[email protected]> wrote: > Hi David, > > But it is not a NUG coordinate variable has, by definition, the same name > as a dimension (see http://www.unidata.ucar.edu/ > software/netcdf/docs/netcdf_data_set_components.html#coordinate_variables > ) ... so height, in the example below, is not a NUG coordinate variable. It > is an auxiliary coordinate variable, if you follow the definitions we have > in the CF convention. > > Martin > ________________________________ > From: David Hassell [[email protected]] > Sent: 31 July 2017 09:33 > To: Juckes, Martin (STFC,RAL,RALSP) > Cc: CF Metadata > Subject: Re: [CF-metadata] Use of axis attribute in an auxillary coordinate > > Hi Martin, > > Because it's numeric, I would say that it acting as a coordinate variable > in the NUG sense. > > All the best, > > Daivd > > On 31 July 2017 at 09:18, <[email protected]<mailto: > [email protected]>> wrote: > Hello David, > > yes, so "height" in the example I gave is clearly an auxiliary coordinate, > right? > > cheers, > Martin > > ________________________________ > From: David Hassell [[email protected]<mailto: > [email protected]>] > Sent: 31 July 2017 09:03 > To: Juckes, Martin (STFC,RAL,RALSP) > Cc: CF Metadata > Subject: Re: [CF-metadata] Use of axis attribute in an auxillary coordinate > > 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]<mailto: > [email protected]><mailto:[email protected]<mailto: > [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< > http://cicsnc.org><http://cicsnc.org> > > <mailto:jbiard<mailto:jbiard><mailto:jbiard<mailto:jbiard>> at > cicsnc.org<http://cicsnc.org><http://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<http://stfc.ac.uk>< > http://stfc.ac.uk> > > <mailto:martin.juckes<mailto:martin.juckes><mailto:martin.juckes > <mailto:martin.juckes>> at stfc.ac.uk<http://stfc.ac.uk><http://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<http://cgd.ucar.edu>< > http://cgd.ucar.edu> <mailto:CF-metadata<mailto:CF-metadata><mailto: > CF-metadata<mailto:CF-metadata>> at cgd.ucar.edu<http://cgd.ucar.edu>< > http://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<http://cicsnc.org><http://cicsnc.org> <mailto: > jbiard<mailto:jbiard><mailto:jbiard<mailto:jbiard>> at cicsnc.org< > http://cicsnc.org><http://cicsnc.org>> o: +1 828 271 4900 > <tel:%2B1%20828%20271%204900><tel:%2B1%20828%20271%204900> > > <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<http://cgd.ucar.edu>< > http://cgd.ucar.edu> > > <mailto:CF-metadata<mailto:CF-metadata><mailto:CF-metadata<mailto: > CF-metadata>> at cgd.ucar.edu<http://cgd.ucar.edu><http://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 5613<tel:%2B44%20118%20378%205613> > <tel:%2B44%20118%20378%205613>http://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<http://cicsnc.org><http://cicsnc.org> <mailto:jbiard > <mailto:jbiard><mailto:jbiard<mailto:jbiard>> at cicsnc.org< > http://cicsnc.org><http://cicsnc.org>> o: +1 828 271 4900 > <tel:%2B1%20828%20271%204900><tel:%2B1%20828%20271%204900> /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]<mailto:[email protected]><mailto: > [email protected]<mailto:[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<tel:%2B44%20118%20378%205613> > http://www.met.reading.ac.uk/ > > > > -- > 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/ > -- 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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