Hi Dan, Your example looks correct to me. Not that I'm an expert or anything, but if you *are* confused, at least you're not alone. :)
Cheers, --Seth On 12/17/2015 4:35 AM, Hollis, Dan wrote: > Hi all, > > I thought I understood coordinates until I read this post :-) > > I've waded through much of #104 and re-read some bits of the CF convention > and NUG. As far as I can tell both 'auxiliary coordinate variable' and > 'scalar coordinate variable' are concepts introduced by CF i.e. they don't > exist in the NUG. Is that correct? > > In an attempt to help myself understand all the different flavours of > coordinate I've put together the following simple example that I think > demonstrates all the possibilities. > > > dimensions: > x = 180; > y = 290; > p = 1; > n = 5; > > variables: > float d(y, x, p, n); > d: coordinates = "lat lon h s a z t"; > > float x(x); # coordinate variable > float y(y); # coordinate variable > float p(p); # size 1 coordinate variable > > float lat(y, x); # auxiliary coordinate variable > float lon(y, x); # auxiliary coordinate variable > float h(p); # size 1 auxiliary coordinate variable > char s(n); # string-valued auxiliary coordinate variable > char a(p); # size 1 string-valued auxiliary coordinate variable > > float z; # numeric scalar coordinate variable > char t; # string-valued scalar coordinate variable > > > Is this a valid example? Have I missed anything out, or completely > misunderstood some aspect? I hope I'm not creating further confusion... > > Regards, > > Dan > > > > -----Original Message----- > From: CF-metadata [mailto:[email protected]] On Behalf Of > [email protected] > Sent: 17 December 2015 09:04 > To: [email protected] > Cc: [email protected] > Subject: Re: [CF-metadata] On scalar coordinate variables > > Hi David, > > In case (1) "double dim1" is a an NUG scalar coordinate variable. My point is > that the #104 text appears ambiguous to me, because it is using the term > "scalar coordinate variable" in a way which is different from the NUG usage, > but at the same time relies on reference to the NUG text for definitions of > coordinate variables, > > regards, > Martin > ________________________________________ > From: David Hassell [[email protected]] > Sent: 16 December 2015 23:38 > To: Juckes, Martin (STFC,RAL,RALSP) > Cc: [email protected] > Subject: Re: [CF-metadata] On scalar coordinate variables > > 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 > _______________________________________________ > CF-metadata mailing list > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
