vtkTriangleFilter leads to hole in mesh

Support
1

I have a polydata that is comprised of quads. When I triangulate it, the mesh has a hole. Why?

In the screenshot below, left is the original polydata, right is post triangulation.

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image1919×1030 216 KB

For comparison, when I tetrahedralize it, then extract the surface, no hole appears: (left is post triangulation, right is tetrahedralize → extract surface)

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image1919×1030 223 KB

Why does this happen? Is there something to be aware about my mesh or is this something weird happening vtk-side?

Posting in vtk rather than paraview forum because I’m assuming that triangulate = vtkTriangleFilter and tetrahedralize = vtkDataSetTriangleFilter

Here’s the mesh itself:
clip_original.vtp (4.7 KB)

Thanks!

2

I do not know completely why, maybe someone with more knowledge about that algorithm could comment.

That quad in particular looks concave to me. Maybe that is why the earcut triangulation algorithm (which is in use by vtkTriangleFilter) is skipping it.

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Any particular reason to triangulate? The rendering process in VTK already pretriangulates the mesh properly before rendering (that is why the quads render fine)

3

I also confirmed in VTK 9.5 and ParaView 6.0.1. I created an issue to track this: https://gitlab.kitware.com/vtk/vtk/-/issues/19808