Hi Richard,
I'm confused by 1). Could you explain further?
It sounds like what you mean is that you want to propose that the
basetime specified by the units attribute should not have an offset
specifier after the date-time if the calendar is not real-world.
That makes sense, although I don't think I would support it. In
regional climate modeling, people are concerned about things like
the diurnal cycle, so there are cases where it would be convenient
to define the base time such that the day boundaries align with
local midnight. (We didn't do that in NARCCAP, but we did consider
it as an option.)
Regardless, if there's no offset specified, the time coordinate still
needs to be pinned down by having it be relative to some particular
point on the globe. If you feel the need to make a distinction
between UTC in real-world calendars and the logical equivalent
(GMT, I suppose) in non-real-world calendars, that's fine, but I
would say to do so very carefully; I think it would cause more
confusion than it would clear up to just say that the statement in
section 4.4 doesn't apply to non-real-world calendars...
Cheers,
--Seth
On Mon, 1 Jul 2013 13:26:22 +0000
"Hattersley, Richard" <richard.hattersley at metoffice.gov.uk> wrote:
>Hi everyone,
>
>I'd like to propose a trac ticket or two to clarify the meaning when using
>alternative calendars. But before I do that I'd like to check for community
>opinion (or even consensus!?) ...
>
>1. Time zones should be excluded/banned when using non-real-world calendars.
>For example, the statement in section 4.4 of "if the time zone is omitted the
>default is UTC" should not apply.
>
>2. The "months since" and "years since" semantics for non-real-world calendars
>need defining/outlawing. e.g. The UDUNITS definition of a year as
>365.242198781 days makes no sense at all for a 360-day calendar, but in this
>particular case a year could be unambiguously defined as 360 days.
>
>3. The year-zero semantics for non-real-world calendars need defining. From
>section 7.4, "Year 0 may be a valid year in non-real-world calendars".
>
>I have some further questions concerning real-world calendars, but as with all
>things dealing with the real world they are a little more messy so I'll save
>them for another post.
>
>Richard Hattersley
>Benevolent Dictator of Iris - a CF library for Python:
>www.scitools.org.uk/iris<http://www.scitools.org.uk/iris>
>Met Office FitzRoy Road Exeter Devon EX1 3PB United Kingdom
>Tel: +44 (0)1392 885702
>Email:
>richard.hattersley at metoffice.gov.uk<mailto:richard.hattersley at metoffice.gov.uk>
> Web: www.metoffice.gov.uk<http://www.metoffice.gov.uk/>
>
Received on Tue Jul 02 2013 - 13:50:52 BST
