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
