OK, I've raise an issue here:
https://github.com/cf-convention/cf-conventions/issues/174
cheers,
Martin
________________________________
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of Jonathan Gregory <j.m.gregory at reading.ac.uk>
Sent: 12 July 2019 13:53:45
To: cf-metadata at 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.juckes at stfc.ac.uk> -----
> Date: Fri, 12 Jul 2019 08:43:33 +0000
> From: Martin Juckes - UKRI STFC <martin.juckes at stfc.ac.uk>
> To: Jonathan Gregory <j.m.gregory at reading.ac.uk>, "cf-metadata at cgd.ucar.edu"
> <cf-metadata at 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-bounces at cgd.ucar.edu> on behalf of Jonathan Gregory <j.m.gregory at reading.ac.uk>
> Sent: 10 July 2019 17:55
> To: cf-metadata at 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.Evans at niwa.co.nz> -----
>
> > Date: Tue, 9 Jul 2019 23:08:46 +0000
> > From: Tom Evans <Tom.Evans at niwa.co.nz>
> > To: Jonathan Gregory <j.m.gregory at 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 at 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-bounces at cgd.ucar.edu> On Behalf Of Jonathan Gregory
> > Sent: Tuesday, 9 July 2019 12:42 AM
> > To: cf-metadata at 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.Evans at niwa.co.nz> -----
> >
> > > Date: Mon, 8 Jul 2019 01:51:19 +0000
> > > From: Tom Evans <Tom.Evans at niwa.co.nz>
> > > To: "cf-metadata at cgd.ucar.edu" <cf-metadata at 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 at 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 at cgd.ucar.edu
> > > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
> >
> >
> > ----- End forwarded message -----
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> > CF-metadata at cgd.ucar.edu
> > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
> >
> >
> >
>
>
>
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Received on Tue Jul 16 2019 - 06:54:35 BST
