Dear all,
I would like to add one aspect that hasn't been mentioned yet, namely
the numerical side of the story. It depends on the numerical scheme used
whether quantities represent values in cells or values at grid corners
that should be interpreted as continuous (often linear) functions in
between. Staggered schemes and finite volume methods in general lead to
state quantities that can be mapped to average quantities within certain
cells (e.g. average water level). However, collocated schemes and finite
element methods often lead to quantities defined at nodes that are
continuous functions. We're working with some codes, e.g. wave model
SWAN, that provide data on gridpoints that should not be interpreted as
values valid for some grid cell. For this reason I would object against
default bounds since there is no way that one can undo the association
with cell bounds.
I do support the idea of including boundaries whenever appropriate. I
think that explicit (or implicit) cell bounds will also play an
important role in the mapping between netCDF CF and OGC concepts.
Best regards,
Bert
-----
Karl Taylor wrote:
Dear all,
I agree that in cases where bounds are appropriate, they should always
be included. I'm not sure, however, how the checker would know in
which cases they should be included.
So, we'll have to be careful in how we word the recommendation, and
perhaps the checker won't be able to raise a warning when they aren't.
regards,
Karl
On 8/11/11 11:33 PM, Jonathan Gregory wrote:
Dear Karl
I agree with Karl about this:
I'm not sure why we should assume anything if the bounds are
missing. Making an assumption would be valuable if the absence of
bounds invariably implied a rule (e.g., centers half-way between
bounds), but otherwise the assumption could be wrong, so what have
we gained?
...
It might especially be difficult to decide where to place the bounds
in the case of unevenly spaced grid-points.
While I agree we should not assume a default for missing bounds, I think it
would be good to recommend that bounds should be included. At present we do
not do this. If we made it a recommendation (in section 5.1), the CF_checker
would give a warning if there were no bounds.
Cheers
Jonathan
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