Hi Martin, I've just come back to this. I think you're right that #104 refers to your case (2), but is that because in case (1), "double dim1" is a CF data variable and not a CF scalar coordinate variable?
Thanks, David ---- Original message from [email protected] (09AM 09 Dec 15) > Date: Wed, 9 Dec 2015 09:07:22 +0000 > From: [email protected] > To: [email protected] > CC: [email protected] > Subject: RE: [CF-metadata] On scalar coordinate variables > > Hi David, > > Aren't there two cases here, one in which the scalar coordinate does have the > same name as a dimension and one in which it doesn't? i.e. > > (1) scalar NUG coordinate variable > Dimensions: > dim1 = 1 ; > variables: > float myvar(dim1); > double dim1; > > (2) Scalar CF coordinate variable > variables: > float myvar; > myvar: coordinates= "dim1" ; > double dim1; > > I see that ticket 104 assumes that the term "scalar coordinate variable" only > refers to the 2nd example, but example (1) is declares a valid coordinate > variable in the NUG sense which is also a scalar. If CF wants to exclude > this, it needs to be explicitly stated that it is not allowed (or, if it is > already excluded by the convention somehow, this restriction relative to the > NUG convention should be clarified). > > I'm not sure that the reference to NUG is incorrect .. I certainly didn't > mean to assert that. I have the impression the NUG usage here is what users > expect and so it should be in the CF convention and the other parts of the > convention should be consistent. In what sense do you think it is incorrect? > > Regards, > Martin > > -----Original Message----- > From: David Hassell [mailto:[email protected]] > Sent: 08 December 2015 14:19 > To: Juckes, Martin (STFC,RAL,RALSP) > Cc: [email protected] > Subject: Re: [CF-metadata] On scalar coordinate variables > > Hello Martin, > > I think that a CF scalar coordinate variable is not a NUG-defined coordinate > variable because it does not have the same name as a dimension. > > Nor is it a special type of CF coordinate variable, as was discussed in > ticket #104 http://cf-trac.llnl.gov/trac/ticket/104 - it could be > functionally equivalent to an auxiliary coordinate variable. > > However, section 1.3 makes it clear (in italics, no less) that > > "The use of [NUG-defined] coordinate variables is required for all > dimensions that correspond to one dimensional space or time > coordinates" > > which as you point out is incorrect. Perhaps that is where a clarification > should go, i.e.: > > "The use of coordinate variables or scalar coordinate variables (as > defined in section 5.7) is required for all dimensions that > correspond to one dimensional space or time coordinates" > > What do you think? > > All the best, > > David > > ---- Original message from [email protected] (09AM 08 Dec 15) > > > Date: Tue, 8 Dec 2015 09:58:29 +0000 > > From: [email protected] > > To: [email protected] > > Subject: [CF-metadata] On scalar coordinate variables > > > > Hello, > > > > The CF Convention 1.6 and draft 1.7 both include, in the discussion of > > dimensions in Section 2.4, the statement that: > > "It is also acceptable to use a scalar coordinate variable which eliminates > > the need for an associated size one dimension in the data variable." > > > > However, the convention states that coordinate variables should be > > interpreted as 'NUG-defined "coordinate variables."'. The NUG is vague > > about the definition ( > > https://www.unidata.ucar.edu/software/netcdf/docs/coordinate_variables.html > > ), but it does say "Current application packages that make use of > > coordinate variables commonly assume they are numeric vectors and strictly > > monotonic". It also states that "A position along a dimension can be > > specified using an index", which is not consistent with the use of a scalar > > coordinate variable. > > > > One application which appears to assume that coordinate variables are > > vectors is the CF Checker, so we need some clarification. I'm not sure how > > other applications deal with it. > > > > The problem with the current phrasing in the CF Conventions document is > > that it suggests the NUG approach is being followed and then introduces a > > departure from the NUG approach in a separate part of the text. > > > > I would recommend either adding after 'NUG-defined "coordinate variables"' > > a clarification '(that is a scalar or vector variable with the same name as > > a dimension)', or changing the statement about use of scalar coordinate > > variables. > > > > regards, > > Martin > > _______________________________________________ > > CF-metadata mailing list > > [email protected] > > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > > > -- > 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] -- 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
