Dear John
> http://www.unidata.ucar.edu/software/netcdf-java/CDM/DateTime.html
>
> If there's interest, I can propose as a CF convention. Otherwise it
> can remain a CDM extension.
Thank you for doing this. I think it's an attractive idea to have calendar
handling in CF time coordinates. One issue to be dealt with would be the
need to be able to process these strings using any programming language
which might be used to process CF-netCDF data. Could the software be ported
to other languages in which the netCDF lib exists? In order to do calculations
with times, which are often necessary, we need to be able to convert them into
a form which has a fixed-length unit since a reference time (like udunits),
even though that isn't the most convenient way to express them.
What you have proposed for the syntax looks very sensible to me. I have some
minor points:
* A bit related to Don's: it would be good to allow SI prefixes, like udunits
does. For instance, ms is the usual SI symbol for millisecond.
* What happens if n months or n years since a certain date is not a valid
date in the calendar? You probably have a rule to resolve that. Most safely,
it should be an error to encode such a time, I suppose (e.g. 1 year since
29 Feb 2008). Do you insist that the ref data is valid in the calendar?
* The udunits ref time implies missing components e.g. 1 hour since 2011-1-1
means 1 hour since 00:00 on 2001-1-1. What do missing components of ISO strings
imply in your implementation? I think it has got to imply something, because
these datetimes are still complete time specifications, aren't they.
* For further udunits compatibility, it would be convenient to be able to omit
the time zone, which would imply Z. All global model data is in UTC, I should
think, and I suppose it must be the obvious choice for all global datasets.
I think that we should use standard_names of time for datetimes only, and other
words, such as period, for intervals of time in standard_names. Then we can
give them different sorts of units.
Best wishes and thanks
Jonathan
Received on Thu Aug 18 2011 - 09:41:53 BST
