[CF-metadata] Proposal for better handling vector quantities in CF

From: John Caron <caron>
Date: Fri, 09 Dec 2011 12:43:18 -0700

On 12/9/2011 11:37 AM, Jonathan Gregory wrote:
> Dear John
>
> I prefer the idea that Thomas has put forward of an umbrella, rather than
> containing the vector/tensor components in one data variable, because
>
> * I really don't like the idea of units being mixed within a data variable.
> I think things with different units must certainly be different quantities
> and could not be regarded as the same field. You can get away with it if they
> are all m s-1, for instance, but not so easily if the vertical one is orders
> of magnitude different from the horizontal, and not at all if the vector is
> expressed in polar coordinates.

I think the common case is that the vector components have the same
unit. One could restrict to that case.

>
> * I think it would be very inconvenient, and would break a lot of existing
> software, if the coordinates were not what they appeared to be, because an
> offset had to be added. Also, in general, the component fields of a staggered
> grid do not have the same dimensions, as well as differing in the coordinates.
Im not sure what "an offset had to be added" means.

I think the common case of staggered grids could be handled with a
convention defining the staggering, rather than seperate dimensions. I
pull out the one Rich Signell and I cam up with a long time ago, for its
own sake.

>
> * It avoids the need to define a convention for labelling vector/tensor
> components.
I think this convention would be about as complex as the one you will
need for Thomas' proposal.

>
> * It is completely backwards-compatible as regards the component fields, which
> are exactly as before; we're just adding some separate information linking
> them. This seems neat to me.

I agree thats a strong reason for Thomas' method.

OTOH, if we start thinking in terms of the extended model, a Structure
("compound type" in HDF5 parlance) might be useful. What do you think
about starting to think about possible uses of extended data model?

Thanks for your thoughts, as always, interesting.

John
Received on Fri Dec 09 2011 - 12:43:18 GMT