I think it's good to remove the dependence on UDUNITS from the CDM for date handling.
However, although "date" is not a unit of measure, "seconds" is, and so is "month" in the definition of UDUNITS. Since CF defines that we use the UDUNITS interpretation of month/year, it would seem dangerous to change this assumption for backward compatibility? (It's not just that months are of variable lengths within a year, but also that there are different definitions of a "month". UDUNITS uses a fixed year-length (not a calendar year length) and a month is year/12.) BTW, the various calendars are implemented in ncWMS at http://www.resc.rdg.ac.uk/trac/ncWMS/browser/trunk/src/java/uk/ac/rdg/resc/edal/time. I even wrote half-decent unit tests - aren't I a good boy? ;-) Jon -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of John Caron Sent: 15 March 2011 13:02 To: [email protected] Subject: Re: [CF-metadata] udunits handling of fuzzy time units On 3/15/2011 5:03 AM, Karl Taylor wrote: > I agree with Jon. > > By definition, I think, a "unit of measure" must not vary; hence month > is not a proper unit and not only depends on month of year, but also > on assumed calendar (and similarly for year). Therefore, I think > "months since" and "years since" should not be allowed in CF. > > Karl Hi Karl: so if currently we cant actually use months and years, because of the way udunits handles them, why not redefine how they should be understood when you do use them, namely as setting the month or year field in a date calculation. this eases the burden on data writers, and makes the metadata human readable, at the cost of a small increase in the complexity of libraries that read data. one more comment: a date is not a unit of measure, and therein lies all the trouble. IMO, date handling should be removed from the udunits package, which is what im doing now in the CDM (not removing date handling from udunits, just not using udunits anymore to handle dates). John _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
