This message came from the CF Trac system. Do not reply. Instead, enter your comments in the CF Trac system at https://cf-pcmdi.llnl.gov/trac/.
#105: Scalar Coordinates -----------------------------+---------------------------------------------- Reporter: markh | Owner: [email protected] Type: enhancement | Status: new Priority: medium | Milestone: Component: cf-conventions | Version: Resolution: | Keywords: -----------------------------+---------------------------------------------- Comment (by jonathan): Dear Mark You say that ticket 104 proposes a change in the interpretation of scalar coordinate variables, and that it would make some existing datasets invalid. I have to say that I think both of these statements are incorrect. As you know, I think the interpretation proposed in ticket 104 is not only the intention of the convention when it was written, but also the most obvious and simplest interpretation of the existing text. However, this debate demonstrates that it's not the only possible interpretation, and I can't argue that yours is definitely excluded by the existing text. But I would emphasise, as I've said before, that adopting 104 does not invalidate any existing dataset. I think that the examples you have given of datasets not OK with 104 but OK with 105 are all legal CF-netCDF files, and would remain so if we clarified the convention as 104 proposes, but they are not good examples of CF-netCDF files. For instance, why would you not make a single model level number and the corresponding single vertical coordinate value belong to the same (size- one) dimension? They are very likely to belong together. It is hard to imagine how it could be useful to have ''independent'' multivalued coordinates of model level number and vertical coordinate. If they are not independent when there are two levels, why would it be useful ''not'' to indicate their relationship when there is only one level? I would argue that a file is deficient, though not invalid, if it does not show this relationship. In another example, you write concerning time (i.e. forecast time), forecast reference time (i.e. analysis time) and forecast period, that "The models which output data don't define the nature of the three time coordinate inter-relationship; they only define that there are two degrees of freedom." This sounds bizarre to me. I find it hard to imagine the writer of the data (or the writer of the software which created the data) thinking, "There are three variables but only two independent dimensions and I want to leave it deliberately vague which are the dimensions." I think it is more likely that this is a degenerate case of a system which has defined relationships between one or two multivalued coordinates in general. One interesting possibility is that it might be one of a collection of forecasts, with various times and forecast reference times, that don't constitute a 2D array. In that case there could be a single discrete axis (CF section 4.5), with no coordinate variable, and all three coordinates would be auxiliary. There's only ''one'' dimension in this case. How can you be sure that there are two dimensions (but not which two they are) if all three of the coordinates are single-valued? I think it is best to record the relationship which is most appropriate to the system which generated the dataset, but you may wish to reinterpret the data if a different description is more convenient. You write that "104 is driving a change in my behaviour as a data creator, where as 105 is enabling me to carry on as I currently work." I would say that 104 does not ''force'' anyone to change how they write single-valued coordinates, but it might strongly ''encourage'' them to clarify their intentions by writing more informative CF-netCDF files. Best wishes Jonathan -- Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/105#comment:8> 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.
