Taking CrossSections of Volumetric Data

I am plotting some volumetric data as (x,y,z)->w and using a mapContour+
ContourWidget to view the (Linear3DSet) 64x64x64 data.

I would like to try several display/speed up trade offs but I haven't
yet been able to figure how to do some things with visad.

1. how does one get or display planar sections? 
2. is there a way of adding a clipping plane to see "inside" the volume?
3. are there routines which will "re-sample" the data at a lower rate?

TIA
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