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[netCDF #XLE-976716]: Indices or Labels as Coordinate Variables



Let me suggest you post this question to the netcdf mailing list
and/or the CF conventions mailing list. You are likely to get a more
detailed explanation and solution.

> 
> 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 “serial 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:imagec972de.PNG@a92acecf.4181a3f7]<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
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> 
> 
> 
> 
> 

=Dennis Heimbigner
  Unidata


Ticket Details
===================
Ticket ID: XLE-976716
Department: Support netCDF
Priority: Normal
Status: Open
===================
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