[Paraview] Odd problem slicing/cutting complex polyhedron

[Joachim Pouderoux]

Andy,

ParaView uses vtkPolyhdron data-structure to store polyhedron.
As you can read on this page
<https://www.vtk.org/doc/nightly/html/classvtkPolyhedron.html#details>,
vtkPolyhdron requires:
*"The polyhedron should be watertight, non-self-intersecting and manifold
(each edge is used twice)."*

Clearly, your cell here is not watertight (see attached picture), so I fear
you won't be able to
process it correctly with VTK based tools.

Best,

* Joachim Pouderoux*, Ph.D.

*Technical Lead - Scientific Visualization Team*
*Kitware SAS <http://www.kitware.fr>*



Le jeu. 7 juin 2018 à 17:36, Andrew Parker via ParaView <
paraview at public.kitware.com> a écrit :

> Hi,
>
> I have attached two files.  One is a single-cell complex polyhedron which
> I wish to be able to use and visualise (as is, without tessellation and
> tetrahedralization).  Using 5.5.0 this fails to slice/cut in paraview in
> any major plane.  Paraview complains about non-manifold (under-connected)
> edges.  To debug I wrote out as a vtkPolyData containing all the faces of
> this single cell polyhedron.  This polyData Slices/cuts just fine.  All
> faces added to the vtp file as VTK_POLYGON, likewise are added as a
> face-stream when added as a VTK_POLYHEDRON to the vtu file.  To be clear, I
> write the faces out to the vtp in the same loop I build the faces for the
> single cell vtu mesh, so they are carbon copies of the faces, including
> numbering, ordering etc.  I am aware there are more vertices in the file
> than need be (27 rather than 19), but it was easier...
>
> My working assumption is that there is no problem visualising and working
> with cells of this type (non-convex) in paraview (real use cases includes a
> mesh with many of these types of cells).  Clarity on this point would also
> be good…
>
> I believe paraview should work for concave cells and I suspect it’s a bug
> (either in paraview or my face-data) because if I use 5.4.1 (or indeed
> 5.2.0) I can clip the singleCell in the x-plane (with inside-out flag
> on/off) and I get the expected results. However, in the y and z planes I do
> not get the expected results and those versions either return an empty
> result or the whole cell.  I get no results in 5.5.0 regardless of plane.
> Finally, I get no results in 5.5.1 either.  So it sort of used to work in
> earlier versions depending on the plane of slicing, but now does not.
>
> I’m not sure what I’m doing wrong, can somebody shed some light or spot an
> error in the attached file?  This may be linked to:
>
> https://gitlab.kitware.com/paraview/paraview/issues/18003
>
> Thanks again,
> Andy
>
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