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#107: CF Data Model 1.7 -----------------------------+---------------------------------------------- Reporter: markh | Owner: [email protected] Type: task | Status: new Priority: medium | Milestone: Component: cf-conventions | Version: Resolution: | Keywords: -----------------------------+---------------------------------------------- Comment (by markh): I have a set of questions regarding the proposed text for [wiki:Ticket107Text9Nov13Transforms transforms] #70 contains an approved change which will be incorporated into CF1.7 enabling coordinates to be explicitly linked to particular grid_mapping attributes in a file. This facility is not supported by the description of transforms proposed above. I think that we have two types of information represented here. 1. We have coordinate reference systems which individual coordinates may be defined with respect to. 1. We have coordinates which may be derived from other coordinates and additional information. I wonder whether we can address case 2 by providing a derived coordinate type: rather than focusing on the action and having a transform type, we focus on the goal, the coordinate. Case 1 may then be addressed by providing a coordinate reference system type whose sole job is to give context to the horizontal spatial coordinate, just like a calendar definition does for a time coordinate. grid_mapping attributes from CF1.5 and before were provided to enable the relationship between coordinate variables and [http://cf- pcmdi.llnl.gov/documents/cf-conventions/1.6/ch05s06.html true latitude and longitude coordinates]. As CF-NetCDF also mandates that latitude and longitude coordinates must be supplied, this information is being duplicated (for good reason, I am not questioning the utility of this approach). In this context singular grid_mapping attributes, as in CF1.5, are transforms, or derived coordinates, depending on your point of view, providing latitude and longitude coordinate derivations; these coordinates happen to exist explicitly in netCDF files, for convenience. The singular grid_mapping attribute is also a coordinate reference system definition for the axis=X and axis=Y coordinates of the data variable. CF1.7 introduces a richer syntax, but it does not change the core semantics, that we would like to define horizontal spatial coordinates with respect to a coordinate reference system. Use of the CF1.7 (#70) syntax does not imply derived coordinates, in my opinion, it is a clear signal that only case 1 applies. Does this approach make logical sense? -- Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/107#comment:17> 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.
