Dear all I think that we should be very cautious about backwards-incompatibility, even when changing CF versions. I would be worried about making a change which means metadata would have a different meaning according to which version of the convention is used. I know in principle it is safe because the file states the version, but I don't think we can depend on the version to be coded correctly, or on software to make correct use of it. Although these are errors, we ought nonetheless to design the convention to be as robust as possible in an error-prone world.
Therefore I don't think it is safe to change the the default calendar from gregorian to proleptic_gregorian, because that could change the date you get for a given time coordinate. However, I do think it would be safe to make it illegal to use the default calendar for reference dates earlier than 1582-10-15, or for negative time coordinates (to make sure that dates before 1582-10-15 cannot be specified). In that case, real-world data for which there is no problem would be unaffected, but software would reject time coordinates whose interpretation is problematic. Software could provide an option whereby the user could state what the calendar actually is, when not specified, in order to override the error if the user knows what it truly is. Alternatively, they could easily repair the file with ncatted or some such tool. It should still be possible to use the real-world calendar before 1582-10-15, because CF might be used for real-world historical data earlier than that date, but it would be necessary to state the calendar explicitly. Best wishes Jonathan _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
