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#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 caron): Hi all: From my POV, CF Conventions have not previously made any clear semantic distinction between coordinate variables and auxiliary coordinate variables. Now tickets 104 and 105 seem to have that as an important distinction. Yet the main difference between the two, monotonicity, has no effect on a scalar coordinate. FYI, in the CDM data model, there is no real difference between coordinate variables and auxiliary coordinate variables, bot between scalar and non- scalar coordinates. However, maybe there should be if we can figure it out. Im guessing that the real issue is with the data model, for which I apologize for not having followed. Perhaps thats what I need to do next in order to have anything useful to say. In terms of the actual wording: "The use of scalar coordinate variables is a convenience feature which avoids adding size one dimensions to variables. A numeric scalar coordinate variable has the same information content and can be used in the same contexts as a size one numeric coordinate variable. Similarly, a string-valued scalar coordinate variable has the same meaning and purposes as a size one string-valued auxiliary coordinate variable (Section 6.1)." "If a string-valued auxiliary coordinate variable has only one dimension (the maximum length of the string), it is a string-valued scalar coordinate variable (see Section 5.7, Scalar Coordinate Variables). As such, it has the same information content and can be used in the same contexts as a string-valued auxiliary coordinate variable of a size one dimension which has not been added to the data variable. This is a convenience feature." both seem quite good. This sentence: "If a data variable has two or more scalar coordinate variables, they are regarded as though they were all independent coordinate variables with dimensions of size one. If two or more single-valued coordinates are not independent, but have related values (for instance, time and forecast period, or vertical coordinate and model level number, Section 6.2), they should be stored as coordinate or auxiliary coordinate variables of the same size one dimension, not as scalar coordinate variables." implies a distinction between "independent coordinate variables" and "not independent coordinate variables", and indictates how to use the dimensions of a variable to convey which is which. My gut instinct is that dimension usage is actually already overloaded, and in the absence of a data model which would spell out the implications, we are probably making things unnecessarily complex and confusing with this addition. What I would need to accept either proposal is a working definition of "dependent" and "independent", esp reletive to "coordinate variable" and "auxiliary coordinate variable". Is it true that a "coordinate variable" must be independent ? Is an "auxiliary coordinate variable" always dependent, or can it be either? or? Regards, John -- Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/104#comment:44> 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.
