[Paraview] Isosurfaces with Hex elements

[John Moore]

It appears I have run into an issue with generating isosurfaces from Hex
elements. I am visualizing high order data, which is discontinuous at the
element interfaces, but continuous within each of the subdivisions used to
visualize the element.

If I create a volumetric isosurface I often get large discontinuities.
However, If I create a slice of the volumetric data and then take an
isosurface of the slice, I obtain isolines without large discontinuities.
When I visualize the isolines and isosurfaces simultaneously, they do not
intersect as they should. It seems very odd that taking a slice and then
taking the isosurface of the slice produces the correct result, while
taking the volumetric isosurface does not.

I think the issue stems from the fact that the isosurfaces for Hexes are
generated by the marching cubes algorithm, which can fail if there are
trilinear terms. I've implemented my own isosurface generation algorithm,
with the same results. I assume some kind of fix has been implemented for
the slice feature or isosurface algorithm in 2D. Can anyone confirm this?
And if so, is there a plan to implement a more robust Hex isosurface
algorithm? Or perhaps I'm on the wrong track here...

Thank you for looking,

John
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