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/.
#104: Clarify the interpretation of scalar coordinate variables -----------------------------+---------------------------------------------- Reporter: jonathan | Owner: [email protected] Type: enhancement | Status: new Priority: medium | Milestone: Component: cf-conventions | Version: Resolution: | Keywords: -----------------------------+---------------------------------------------- Comment (by apamment): After careful reading of both tickets #104 and #105 and the relevant sections of CF 1.6, I have come to the conclusion that I support the approach taken in ticket 104. Therefore I vote to accept #104 and reject #105. I agree that the original intention in section 5.7 seems to have been that scalar coordinate variables represent independent axes. Scalar coordinates are stated to be an alternative to adding a size one dimension, which implies that each one does indeed represent an independent dimension of the data variable. I can't help feeling that if CF had stuck to the COARDS way of doing things, i.e., always requiring the addition of size 1 dimensions to data variables, then this ambiguity about whether scalar coordinates are independent or auxiliary would not have arisen. Perhaps this is something to bear in mind if we are tempted to add any more "convenience features" in the future. I can see how the kind of practices highlighted by Mark may have arisen, but I think it is highly undesirable for data files to be written in which the relationship between the coordinates and auxiliary coordinates is ambiguous. I fully agree with Jonathan and David's position that users of data are free to interchange coordinates and auxiliary coordinates as appropriate for their application of the data. Furthermore, I think the ability to do this in a meaningful way (i.e. correctly interpreting the data) is enhanced by making the relationships between the possible alternative coordinates clear at the time of writing. Not to document these relationships is to supply incomplete and possibly misleading metadata which diminishes the opportunities to reuse the data and interpret it appropriately. I certainly do not think we should change the convention to encourage ambiguous use of either coordinate or auxiliary coordinate variables, hence my rejection of the proposal in ticket 105. I confess to having become rather bogged down when reading the discussion of dimensionality versus degrees of freedom, but John's examples helped me to understand (eventually!) the issue. My feeling is to go with Jonathan's way of doing things, i.e., that scalar coordinates are independent and data with only one real degree of freedom, like John's time series, should be described by adding auxiliary coordinates of size one. I think John's idea of making scalar coordinates dependent is in some ways simpler, but it is a more radical change than the one Jonathan is proposing. I had a look at the CF 1.6 conformance document to see what it says about scalar coordinates. They are referred to in section 7.3 (and also, of course, in the corresponding section of the conventions). The text on cell methods clearly treats scalar coordinates as separate dimensions along which statistical processing may have taken place. For this reason, I think that changing scalar coordinates to being dependent rather than independent is in fact a break with the way things have been done in the past and it risks making CF1.7 incompatible with earlier versions. Regardless of whether we ultimately choose to declare scalar coordinates as dependent or independent, I would advocate the inclusion in the conventions document of as many examples as are necessary to fully illustrate the intended use of both scalar coordinates and auxiliary coordinates. In this way, we can hope to avoid future ambiguities and misunderstandings. Maybe we could even include clearly signposted "Do" and "Don't" examples, showing first how scalar coordinate variables are meant to be used and also how they are ''not'' meant to be used. Best wishes, Alison -- Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/104#comment:65> 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.
