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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 Mark Actually I think may already have the same perspective. You write > I want the ability to add a single valued coordiante to my Field without defining a domain_axis at any time. ... The flexibility that CF NetCDF provides for size one coordinates is a really useful feature that I am worried we are designing away in the model. My understanding is that size-one domain axis constructs preserve this flexibility. This is precisely because, in the CF-netCDF standard, scalar coordinate variables and size-one coordinate variables are regarded as equivalent, which is the flexibility you value. Described in terms of the CF data model, adding a new size-one coordinate to a CF-netCDF data variable means (i) creating a domain axis construct of size one, (ii) creating a dimension coordinate construct having this domain axis (and therefore also of size one), (iii) adding the new size-one domain axis construct to the list of axes which dimension to the data array of the field. Adding a new scalar coordinate to a CF-netCDF data variable is described in the data model by exactly the same steps (i) and (ii), but step (iii) is not taken: the dimensions of the data array are unchanged in the data model representation, just as in the CF-netCDF representation. > Additionally I want the ability to evaluate two or more Fields with single valued coordinates, establish that they share coordinate definitions and that the values are different. At this point I will create a new domain_axis on one Field, a new data dimension, and bind my new two- valued coordinate to this data dimension, aggregating my two Fields into one. In order to aggregate the two fields, they must first both have domain axis constructs in the appropriate quantity e.g. indicated by standard name. For example, one of them might at 1.5 m height, the other at 10 m height. However, in CF-netCDF terms, one of them could be a scalar coordinate variable and the other a size-one dimension coordinate variable, since these are logically equivalent. The process of aggregation combines the size-one domain axis constructs of the separate fields into a domain axis of size two of the aggregated field. > By stating that the domain_axes are all defined by the Field, even if some of them are not evident as data dimensions, I feel I have lost this ability to see domain_axes emerge from my data as I aggregate. In my understanding, the existence of the size-one axis constructs of the two foields is what enables the aggregation to happen. Is this the same process as you describe, but in different words? Best wishes Jonathan -- Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/95#comment:43> 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.
