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#74: Allow sharing of ancillary variables among multiple data variables ---------------------------------------+------------------------------------ Reporter: [email protected] | Owner: [email protected] Type: enhancement | Status: new Priority: medium | Milestone: Component: cf-conventions | Version: Resolution: | Keywords: "ancillary data" "standard name modifiers" ---------------------------------------+------------------------------------ Comment (by jonathan): Dear all Jim's description of what I meant is correct. The original dimension is replaced by a dimension of size one when you collapse it by calculating the statistic. In just the same way, a variable which is a function of longitude, having a longitude dimension of size greater than one, becomes a variable with a longitude dimension of size one when you calculate the zonal mean of it. We record the operation of calculating the zonal mean in `cell_methods` with an entry `longitude: mean`, where `longitude` is the name of the longitude dimension (now of size one). Another example, closer to my suggestion of `measurement`, is a model ensemble. It is possible to have a dimension for ensemble member. It is a common operation to calculate ensemble mean and ensemble standard deviation, and we can record these in `cell_methods` in the same way. I respectfully disagree with Nan about the importance of `cell_methods`. The standard name does not contain the entire description of the data variable. I think it's important to keep in mind that CF metadata is distributed over several attributes, which should always all be considered. The `cell_methods` makes important distinctions about how the values represent variation over coordinates. Its whole purpose is to represent statistical operations, and that's why I've made the suggestion in this ticket, because there seems to be an analogy to me. There is always a statistical operation involved in calculating a value, unless it's truly a point value. Moreover, `cell_methods` is a more flexible attribute than the standard name because it refers to the dimensions, which may have been treated statistically in different ways: for instance, a quantity might be a time-mean and a zonal maximum, or it might be (to address Nan's question) an interannual standard deviation of monthly means (`time: mean within years time: standard_deviation over years` in `cell_methods`). Best wishes Jonathan -- Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/74#comment:45> 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.
