Re: [netcdf-java] Questions about handling dimensionless coordinates

On 5/4/2011 9:51 AM, Jon Blower wrote:


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:

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.




Dr Jon Blower

Technical Director, Reading e-Science Centre

Environmental Systems Science Centre

University of Reading, UK

Tel: +44 (0)118 378 5213 <>

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