Hello David, It makes sense to me. It implies that "height" is not a coordinate variable in the NUG sense, and is therefore an auxiliary coordinate variable. Do you agree with this?
regards, Martin ________________________________ From: David Hassell [[email protected]] Sent: 31 July 2017 10:48 To: Juckes, Martin (STFC,RAL,RALSP) Cc: CF Metadata Subject: Re: [CF-metadata] Use of axis attribute in an auxillary coordinate 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]<mailto:[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]<mailto:[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]><mailto:[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]><mailto:[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]>><mailto:[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><http://cicsnc.org> > <mailto:jbiard<mailto:jbiard><mailto:jbiard<mailto:jbiard>><mailto:jbiard<mailto:jbiard><mailto:jbiard<mailto:jbiard>>> > at cicsnc.org<http://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><http://stfc.ac.uk> > > <mailto:martin.juckes<mailto:martin.juckes><mailto:martin.juckes<mailto:martin.juckes>><mailto:martin.juckes<mailto:martin.juckes><mailto:martin.juckes<mailto:martin.juckes>>> > at stfc.ac.uk<http://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><http://cgd.ucar.edu> >> <mailto:CF-metadata<mailto:CF-metadata><mailto:CF-metadata<mailto:CF-metadata>><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://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 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mailing list [email protected]<mailto:[email protected]><mailto:[email protected]<mailto:[email protected]>><mailto:[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><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<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/ 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