Dear Jonathan, and all,
----- Original Message -----
> It has
> previously been suggested that different components should be in the
> same
> data variable, with a dimension for component, but I prefer your
> solution,
> because the components might have different units (e.g. in the case of
> modulus
> and direction), and they might be on different horizontal grids (e.g.
> for
> an Arakawa C-grid), which makes it undesirable or impossible to store
> them in
> a single data variable.
Of course, I agree with the restriction on units. I am however in doubt if it makes any sense to define vector objects from components that do not share the spatial, height, or time dimensions. A (2d) vector can be instantiated from (minimum) 2 components, if given at a given space/time location. As of today, CF allows Arakawa C-grid constructs where components do not share the same grid. But if I was to reunite these (independent) components into a vector object, I would define 2 vector objects. One for the x vectors (having value 0 for all the y components) and one for the y vectors (having value 0 for all the x components). The two vector fields would not share the same grid. But at least the two components of each vector would share the same locations.
Thus, although I am unsure we should impose it from the convention, e.g. by allowing to define some attributes from the "umbrella" level (such as :coordinates), I see little use for defining vector objects that do not share all their dimensions.
All the best,
Tho,qs (on a French keyboqrd!)
> Furthermore, your solution is more flexible since it
> allows you to have several different decompositions in the same file,
> as you
> say. It is also backwards-compatible; the variables containing
> components are
> described exactly as before, and we have the extra umbrella variable
> showing
> some associations between them, which should not cause a problem to
> any
> existing software.
>
> We would need more standard names, as you say, and these could be
> proposed as
> required. The new standard names would be permitted only with the
> umbrella
> variables, or with ancillaries of the umbrella variables.
>
> Best wishes
>
> Jonathan
--
==========================================
Thomas Lavergne
Norwegian Meteorological Institute
P.O.BOX 43, Blindern, NO-0313 OSLO, Norway
Phone: (+47) 22963364 Fax: (+47) 22963380
Email: t.lavergne at met.no
OSISAF HL Portal: http://osisaf.met.no
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Received on Sun Nov 27 2011 - 03:13:13 GMT
