On 20-02-15 15:40, Jim Biard wrote:
Maarten,
This is life with CF. Just to be sure I understand the details of the
problem, the vertical set of pressure values at one lat and lon is
different from the vertical set at a different lat and lon, correct? Is
there no metric (as in, not just an index) vertical coordinate that you
can construct that doesn't vary across the lat/lon grid?
Yes, that is the case.
As far as the pressure bounds being a variable no user will ever need,
I've got to differ with you. Having an unambiguous, consistent, and
automation-friendly mechanism for declaring bounds is quite useful.
No: it is the _bounds_ the user is interested in, there just isn't a
meaningful use for the pressures themselves. The ozone content is given
for the sub-columns, not at a particular level.
It removes uncertainty and avoids the problems that can develop when a
product is developed by one community of people who say, for example,
"Everyone knows that the grid boundaries are halfway between the grid
points" and then gets used by a community of people who say, "Everyone
knows that the grid boundaries are at the grid points." (I've dealt with
this sort of problem more than once in my career!) If CF had a standard
that stated that an extra element at the end of a dimension was
understood to be an upper bound, then your original proposal would be
fine. Without a standard, your original proposal is non-standard (by
definition), and thus open to conflicting interpretations.
I've felt the same frustration about the inefficiencies of coordinate
grids, but until we define a standard for a more compact representation,
it's what we've got.
Coordinate grids are very efficient compared to the present problem,
where a 3D dummy variable is needed.
And perhaps CF 2.0 is an opportunity to address this.
Best,
Maarten Sneep
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