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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 ngalbraith): Replying to [comment:38 graybeal]: > The problem brings its own solution. it should be fine to let multiple variables share the same ancillary variable, if it makes sense in all respects. For it to make sense when the standard_name needs to have the units of the data variable, all the variables need to have the same units. Hmm, I don't think there's been any question of multiple variables sharing a single ancillary variable; that's already permitted in the standard. We're now at the stage of deciding whether the current standard name modifiers should be ''elevated'' to free-standing standard names, so that these variables no longer carry the target variable(s) as part of the standard_name attribute. The problem now is that standard names have specific units assigned to them, and this does not work for variables like standard_error or detection_minimum, which take their units from their 'data variables'. We would need to change the structure of the standard name table to accommodate this type of name - I'm not sure we have the motivation to do that. > Looks to me like it makes sense for detection minimum to allow this, in some environments it would be a common use case. But I can't figure out a sensible use case for one standard_error variable for multiple variables! Agreed, more or less; however standard_error could still be a stand-alone standard name, so that the concept of the standard name modifier could be retired. The idea here is that the data variable points to the correct standard_error, using the ancillary_variables attribute, and the error variable does not include the standard name of the data variable in its standard_name attribute. {{{ float swt(time,depth,lat,lon); swt:standard_name="sea_water_temperature"; swt:ancillary_variables="swt_std_err"; float swt_std_err(time,depth,lat,lon); swt_std_err:standard_name="standard_error"; swt_std_err:long_name="standard error of sea water temperature" }}} This makes the standard error variable a little less independent - you would not know what it is without looking at other variables in the file. To me, this is not an issue, but it might be important to other people. On the other hand, the current method, where swt_std_err has the standard name 'sea_water_temperature standard_error', ''does not work'' when there are multiple variables with a standard name sea_water_temperature in a file. -- Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/74#comment:39> 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.
