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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 Randy On the email list you asked for an example to explain what I mean. I can't think of an example as such. Would you agree that the standard error of a measured quantity means, in principle, the standard deviation of the values you would get by repeatedly measuring the quantity under the same conditions (as far as you can control the conditions)? I believe that's the idea people have wanted to convey by this modifier. The values are not all exactly the same because of uncontrollable variations in the conditions and the behaviour of the instruments and methods being used to make the measurement. If you did in fact make many measurements and wanted to record them in a CF-netCDF file, it would be natural to have a dimension with an index number (1, 2, 3, ...) running over the values you got. A possible standard name for the coordinate variable containing this index could be `measurement` e.g. {{{ dimensions: measurement=10; variables: float temp(measurement); temp:standard_name="sea_water_temperature"; temp:units="K"; int measurement(measurement); }}} If you calculate the mean or the standard deviation of the measurements, you would use `cell_methods` to record this operation: {{{ dimensions: measurement=1; variables: float temp(measurement); temp:standard_name="sea_water_temperature"; temp:units="K"; temp:cell_methods="measurement: standard_deviation"; }}} It is allowed to omit the dimension and include instead the standard name of the dimension in `cell_methods`. See Section 7.3.4. So we can have "measurement: standard_deviation" in `cell_methods` even if there is no `measurement` dimension. I think we could take that to imply the standard deviation of all possible values this measurement could take, which is what is meant (I think) by the standard error of the measurement. This might be stretching 7.3.4 a bit, and if so, an extra sentence could be inserted to explain this usage of the convention. Is that any clearer? Cheers Jonathan -- Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/74#comment:41> 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.
