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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 davidhassell): Hello, I'd to open up a new topic for discussion - namely '''transform constructs''', but this in no way means stopping the others! I think that the [http://www.met.reading.ac.uk/~david/cfdm_0.7.html current proposal's] definition of a transform construct is a bit confused by trying to be too general, going beyond what CF-1.5 states, so Jonathan and I have tightened it up a bit. It is still the case that transform constructs are contained by a parent field construct, but we have altered their definition to be more precise: ''A transform construct defines a mapping from one set of coordinates which can not geo-locate the field construct's data to another set of coordinates that can geo-locate the field construct's data.'' The proposed full text for this section is: ---- === Transform Constructs === A transform construct defines a mapping from one set of coordinates which can not geo-locate the field construct's data to another set of coordinates that can geo-locate the field construct's data. A transform construct contains * A transform name which indicates the nature of the transformation and implies the formula to be used. A CF-netCDF file does not explicitly record the formula; it depends on the application software knowing what to do. * An unordered collection of variables which correspond to the terms of the transformation formula. The variables may be scalar parameters, pointers to dimension or auxiliary coordinate constructs of the field construct, or pointers to other field constructs. The collection includes the input coordinates being mapped, but not the output coordinates. A transform construct provides geo-locating metadata to all of the dimension and auxiliary coordinate constructs referenced by it. Transform constructs correspond to the functions of the CF-netCDF attributes `formula_terms`, which describes how to compute a vertical auxiliary coordinate variable from components ([http://cf- pcmdi.llnl.gov/documents/cf-conventions/1.6/cf- conventions.html#dimensionless-v-coord CF Appendix D]), and `grid_mapping`, which describes how to compute true latitude and longitude auxiliary coordinate variables from horizontal projection dimension coordinates, or describes the figure of earth for true latitude and longitude coordinate variables ([http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.6/cf- conventions.html#appendix-grid-mappings CF Appendix F]). The transform name is the `standard_name` of a vertical coordinate variable with `formula_terms`, and the `grid_mapping_name` of a `grid_mapping` variable. The scalar parameters are scalar data variables (which should have units if dimensional) named by `formula_terms`, and attributes of `grid_mapping` variables (for which the units are specified by the transform construct). The role of each term in the formula of the transform construct is identified by its keyword in a `formula_terms` attribute, or its attribute name in a `grid_mapping` variable. Note that the transform construct for a CF-netCDF grid mapping of `latitude_longitude` is a special case in which the outputs are the same as the input coordinates. ---- All the best, David -- Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/95#comment:107> 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.
