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#95: Development of CF 1.5 Data Model -----------------------------+---------------------------------------------- Reporter: markh | Owner: [email protected] Type: task | Status: new Priority: medium | Milestone: Component: cf-conventions | Version: Resolution: | Keywords: -----------------------------+---------------------------------------------- Comment (by jonathan): Dear all I apologise for silence on this ticket; I haven't had time in the last couple of weeks, but I do intend to contribute. On the Field construct, I agree we could gather the netCDF-specific comments together. In doing this Mark has produced a somewhat different text from the one we had before, on which Martin provided some suggestions. I'd like to compare these three versions. The CF-netCDF convention does not have a clear statement of the purpose of coordinate or auxiliary coordinate variables, as far as I can see. The nearest I have found is in section 4, where it speaks of both: "The values of a coordinate variable or auxiliary coordinate variable indicate the locations of the gridpoints." Following that, we could say "gridpoint", as Martin suggests, because the bounds are optional, but sometimes the bounds are the important information and the gridpoints are notional (for extensive quantities). "Cells" covers both cases. Perhaps we could say "A dimension coordinate construct provides physical coordinates to locate the cells along a unique domain axis, such that all cells which have the same index along that axis share the same coordinate value, and have a different coordinate value from cells with any other index along the axis" and "An auxiliary coordinate construct provides physical coordinates to locate the cells as a function of their indices along an ordered list of one or more domain axes". That's a bit more formal, but I think it shows the distinctions between the two kinds. I agree with Martin that we could add text such as "In CF-netCDF, a string-valued auxiliary coordinate construct could be represented by a numerical auxiliary coordinate construct with a `flag_meanings` attribute to supply the translation to strings." I think the text already allows for singleton auxiliary coordinate values, because it says that an aux coord construct might refer to only one domain axis (so it could be 1D array with a single element). I think we may have made a mistake in the last bit. I think it should say "CF requires there to be auxiliary coordinate constructs of latitude and longitude if there is two-dimensional horizontal variation but the horizontal coordinates are not latitude and longitude", not "recommends". I believe that's what the start of sect 5 means, but it is obscurely stated. Steve Hankin and I have separately been discussing ways to rephrase it which could be proposed as a defect ticket. Best wishes Jonathan -- Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/95#comment:20> CF Metadata <http://cf-pcmdi.llnl.gov/> CF Metadata This message came from the CF Trac system. To unsubscribe, without unsubscribing to the regular cf-metadata list, send a message to "[email protected]" with "unsubscribe cf-metadata" in the body of your message.
