OK, I've raise an issue here: https://github.com/cf-convention/cf-conventions/issues/174
cheers, Martin ________________________________ From: CF-metadata <cf-metadata-boun...@cgd.ucar.edu> on behalf of Jonathan Gregory <j.m.greg...@reading.ac.uk> Sent: 12 July 2019 13:53:45 To: cf-metadata@cgd.ucar.edu Subject: Re: [CF-metadata] Indices or Labels as Coordinate Variables Dear Martin Ah, I see. I agree that this is a defect now in our text if they have changed what they say. I also agree that we should stick with what we've got i.e. more restrictive, coord vars are 1D, numeric, and monotonic and called the same as their dimension. That's our data model. Best wishes Jonathan ----- Forwarded message from Martin Juckes - UKRI STFC <martin.juc...@stfc.ac.uk> ----- > Date: Fri, 12 Jul 2019 08:43:33 +0000 > From: Martin Juckes - UKRI STFC <martin.juc...@stfc.ac.uk> > To: Jonathan Gregory <j.m.greg...@reading.ac.uk>, "cf-metadata@cgd.ucar.edu" > <cf-metadata@cgd.ucar.edu> > Subject: Re: [CF-metadata] Indices or Labels as Coordinate Variables > > Hello Tom, Jonathan, > > > that is interesting. It looks like a change introduced in NetCDF 4 which CF > has not caught up with. Do you think they really mean what they say about the > values having to be strictly monotonic? > > > The convention does say we use this term "term precisely as it is defined in > the NUG section on coordinate variables", but we also state that it must be > numeric. Perhaps we should take "precisely" out of that sentence (I think it > was true in NetCDF 3)? Keeping string values out of the array dimensions and > preserving a clear rule about monotonicity looks like the best approach to me, > > > regards, > > Martin > > > > ________________________________ > From: CF-metadata <cf-metadata-boun...@cgd.ucar.edu> on behalf of Jonathan > Gregory <j.m.greg...@reading.ac.uk> > Sent: 10 July 2019 17:55 > To: cf-metadata@cgd.ucar.edu > Subject: Re: [CF-metadata] Indices or Labels as Coordinate Variables > > Dear Tom > > That's interesting. I did not know or had forgotten about that Unidata > recommendation. CF doesn't allow string-valued coordinate variables (with > the same name as any of their dimensions), only string-valued auxiliary > coordinate variables. > > Best wishes > > Jonathan > > ----- Forwarded message from Tom Evans <tom.ev...@niwa.co.nz> ----- > > > Date: Tue, 9 Jul 2019 23:08:46 +0000 > > From: Tom Evans <tom.ev...@niwa.co.nz> > > To: Jonathan Gregory <j.m.greg...@reading.ac.uk> > > Subject: RE: [CF-metadata] Indices or Labels as Coordinate Variables > > > > Dear Jonathan > > > > Thanks very much for your response. It really did help me understand the > > use of coordinate values. In particular, your suggestion that an auxiliary > > coordinate variable (with a different name from the dimension) could be > > listed in the coordinate attribute of a variable is very helpful. It > > produces exactly the behaviour I'd look for in Panoply, for example. > > > > I have a follow-up question, if you don't mind: > > > > The Best Practices page at the Unidata site also mentions a "string-valued > > coordinate variable," which has the same name as its first dimension, e.g. > > > > char location(location, loc_len) > > > > where loc_len is the length of a text label for the location. The CF > > specification mentions a "string-valued auxiliary coordinate variable" -- > > something like > > > > char location_name(location, loc_len) > > > > if I'm following this correctly -- which could also be used as a coordinate > > in the attribute -- but it doesn't say anything about a string-valued > > variable with the same name as a dimension. I also haven't found any > > examples that use string-valued coordinate variables named the same as a > > dimension. Would such a variable risk conflict or confusion with the > > assumptions of applicactions designed to work with CF-compliant data? > > > > Cheers > > Tom Evans > > > > > > > > > > > > [cid:image702fcb.PNG@5e3232e3.49822ae5]<http://www.niwa.co.nz> > > > > > > Dr Tom Evans > > Software Developer > > T +64-7-859-1832 > > > > National Institute of Water & Atmospheric Research Ltd (NIWA) > > Gate 10 Silverdale Road, Hillcrest, Hamilton > > Connect with NIWA: niwa.co.nz<https://www.niwa.co.nz> > > Facebook<https://www.facebook.com/nzniwa> > > Twitter<https://twitter.com/niwa_nz> > > LinkedIn<https://www.linkedin.com/company/niwa> > > Instagram<https://www.instagram.com/niwa_science> > > > > To ensure compliance with legal requirements and to maintain cyber security > > standards, NIWA's IT systems are subject to ongoing monitoring, activity > > logging and auditing. This monitoring and auditing service may be provided > > by third parties. Such third parties can access information transmitted to, > > processed by and stored on NIWA's IT systems. > > > > > > -----Original Message----- > > From: CF-metadata <cf-metadata-boun...@cgd.ucar.edu> On Behalf Of Jonathan > > Gregory > > Sent: Tuesday, 9 July 2019 12:42 AM > > To: cf-metadata@cgd.ucar.edu > > Subject: [CF-metadata] Indices or Labels as Coordinate Variables > > > > Dear Tom > > > > It would be a coordinate variable if it's location(location) and in that > > case > > its values have to be unique and monotonic because generic applications > > may make that assumption when plotting or doing computations with them. If > > these are really labels then those operations don't really make sense > > anyway. > > In that case it would be more suitable to store the IDs in an auxiliary > > coordinate variable, which doesn't have the same name as the dimension, and > > is listed in the coordinates attribute of the data variable. Values in aux > > coord variables do not have to be unique or monotonic or even numeric. It is > > not mandatory to include a coordinate variable (in the Unidata sense). > > > > Best wishes > > > > Jonathan > > > > ----- Forwarded message from Tom Evans <tom.ev...@niwa.co.nz> ----- > > > > > Date: Mon, 8 Jul 2019 01:51:19 +0000 > > > From: Tom Evans <tom.ev...@niwa.co.nz> > > > To: "cf-metadata@cgd.ucar.edu" <cf-metadata@cgd.ucar.edu> > > > Subject: [CF-metadata] Indices or Labels as Coordinate Variables > > > > > > I have a question regarding coordinate variables: > > > > > > I am working with time-series data representing hydrological conditions > > > at fixed locations in a stream network. The values are generated by a > > > model at regular time intervals, and I believe that the data will fit > > > well into the timeSeries feature type described in the "Discrete Sampling > > > Geometries" chapter of the CF conventions. For example, we would put all > > > the discharge values into a single 2D array: > > > > > > double flow(time, location) > > > > > > The dimension "location" here is the "instance dimension" described in > > > the convention. > > > > > > I would like to use an integer variable named "location" as a coordinate > > > variable to go along with the location dimension. I think this would > > > provide a handy way for post-processing programs to locate a time series > > > in our model result files. The Best Practices guidance on the Unidata > > > website, though, says that coordinate variables "must be strictly > > > monotonic" and the order of the IDs in my location variable is arbitrary. > > > All of the location values are unique, but the location numbers are > > > essentially numerical labels - location 1524 is distinct from location > > > 2817, but neither is greater than the other in a way that means anything > > > to the model. Location IDs do not consistently increase or decrease > > > traveling downstream, for example. > > > > > > So, is the guidance that coordinate variable should strictly increase or > > > decrease relevant to my case? I've built some sample files and examined > > > them using Panoply, and in Python using xarray. I haven't seen any > > > problems with using non-monotonic integer "ID numbers" as coordinate > > > variables, but that "must" in the guidance troubles me. If my locations > > > are identified by arbitrary numbers, do I run the risk of scrambling the > > > links between my time series and their identifiers? > > > > > > Thanks > > > Tom Evans > > > > > > > > > > > > [cid:image9ef98c.PNG@58bab801.4bad83a3]<http://www.niwa.co.nz> > > > > > > > > > Dr Tom Evans > > > Software Developer > > > T +64-7-859-1832 > > > > > > National Institute of Water & Atmospheric Research Ltd (NIWA) > > > Gate 10 Silverdale Road, Hillcrest, Hamilton > > > Connect with NIWA: niwa.co.nz<https://www.niwa.co.nz> > > > Facebook<https://www.facebook.com/nzniwa> > > > Twitter<https://twitter.com/niwa_nz> > > > LinkedIn<https://www.linkedin.com/company/niwa> > > > Instagram<https://www.instagram.com/niwa_science> > > > > > > To ensure compliance with legal requirements and to maintain cyber > > > security standards, NIWA's IT systems are subject to ongoing monitoring, > > > activity logging and auditing. This monitoring and auditing service may > > > be provided by third parties. Such third parties can access information > > > transmitted to, processed by and stored on NIWA's IT systems. > > > > > > > > > > > > > > > > > > > > > > > > _______________________________________________ > > > CF-metadata mailing list > > > CF-metadata@cgd.ucar.edu > > > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > > > > > > ----- End forwarded message ----- > > _______________________________________________ > > CF-metadata mailing list > > CF-metadata@cgd.ucar.edu > > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > > > > > > > > > > ----- End forwarded message ----- > _______________________________________________ > CF-metadata mailing list > CF-metadata@cgd.ucar.edu > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata ----- End forwarded message ----- _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
