....you could look at the ?standard_error? modifier (CF1.4, appendix C).
This may fail due to the rather strict definition required by CF for
time units attributes, but you could in principle set up a parallel
time_error variable, or similar, with a ?time standard_error? standard
name.
Any thoughts, anybody?
Tim.
On 02/06/2010 16:10, "Jonathan Gregory" <j.m.gregory at reading.ac.uk> wrote:
> Dear Jon
>
> CF doesn't provide a way to do this except by giving bounds. I think that's
> the right thing to do, because the length of the interval alone doesn't say
> when it starts and stops, which applications may need to know.
>
> The cell_methods indicates how the value represents the variation within the
> interval. For an intensive quantity, "point" is the default i.e. instantaneous
> in time. To indicate a mean, cell_methods of "mean" should be specified. You
> are saying it is "representative" in some vaguer way than a mean, and it is
> not
> instantaneous. That sounds like a different cell_methods. Perhaps it would be
> a good idea to allow "cell" to be specified in cell_methods for intensive
> quantities, to indicate a "representative" value in this vague sense. ("cell"
> is the default cell_methods for an extensive quantity, which relates to the
> entire cell and depends on its size.) I think this vagueness should in general
> be discouraged; it would be better to be more precise and specify "mean",
> "median" etc., but if you can't be precise it'd be nice to be able to say so.
>
> What do you think? That would require a small change to the convention.
>
> Cheers
>
> Jonathan
>
>> > We have many datasets for which we need to express the precision of the
>> > time axis. For example, the OSTIA sea surface temperature dataset
>> > contains daily fields. The data are considered "representative" of a
>> > particular day, without necessarily being a simple average over the day.
>> > At the moment the data are registered to 12:00Z on each day, but this is
>> > indistinguishable from an instantaneous snapshot at this time.
>> >
>> > I guess it would be possible to express the temporal precision using the
>> > "bounds" attribute for the variable in question
>> > (http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.4/cf-conventions.ht
>> > ml#cell-boundaries), by specifying the start and end of each day as the
>> > bounds. Is there a less verbose way of providing this information,
>> > perhaps by stating the precision as "1 day/24 hours/whatever" as a
>> > single attribute?
>> >
>> > Jon
>> >
>> > --
>> > Dr Jon Blower
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