On 5/4/2011 9:51 AM, Jon Blower wrote:
Hi,
I'd like to add support for dimensionless vertical coordinates in
ncWMS and I have a few questions:
1.How common is it for the transformation between dimensionless coords
and natural coords to be time-dependent? Under what circumstances
would this occur? Does it happen when the coordinate depends on a
pressure field that varies with time?
yes, thats the common case that ive seen: surface_pressure(time) for
hybrid/sigma coordinates. Im not sure about the ocean vertical coordinates.
2.If the VerticalTransform exists, can I assume that
getCoordinateArray() will always return a valid array, i.e. that nj4
has automatically found all the auxiliary fields necessary to create
the transform (such as pressure)?
yes, it will fail fast (at construction) if theres a problem.
3.I can see how to get the units of the transformed vertical
coordinate (i.e. the "natural" coords, via
VerticalTransform.getUnitString()) but how can I get the "positive"
direction? In other words, if the natural coordinates are in metres,
how do I know whether this is depth or height?
hmm, i never thought of that problem. im guessing a domain expert could
look at these:
http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.5/cf-conventions.html#dimensionless-v-coord
and tell us the right answer, which we could then embed into the code.
4.What would be the most "natural" interpolation method in the
vertical when transforming a gridded field from dimensionless
coordinates into levels -- nearest-neighbour or linear? (Or something
else?)
dunno - id guess linear or log, depending on the transform. perhaps
the domain expert could look at the above list and give some advice.
Thanks,
Jon
--
Dr Jon Blower
Technical Director, Reading e-Science Centre
Environmental Systems Science Centre
University of Reading, UK
Tel: +44 (0)118 378 5213
http://www.resc.reading.ac.uk <http://www.resc.reading.ac.uk/>
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