# Strange display representation of VTK\_POLYHEDRON cells

**URL:** https://discourse.paraview.org/t/strange-display-representation-of-vtk-polyhedron-cells/14612
**Category:** ParaView Support
**Tags:** python, vtk
**Created:** [May 13, 2024, 11:42am UTC](https://discourse.paraview.org/t/strange-display-representation-of-vtk-polyhedron-cells/14612 "2024-05-13T11:42:41Z")
**Posts on this page:** 5
**Page:** 1

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### Author: ![Ieeshka](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/i/ec9cab/32.png) [@Ieeshka](https://discourse.paraview.org/u/Ieeshka)
#### Post date: [May 13, 2024, 11:42am UTC](https://discourse.paraview.org/t/strange-display-representation-of-vtk-polyhedron-cells/14612/1 "2024-05-13T11:42:41Z")

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Hello everybody!

I am a newbie in ParaView and I would appreciate some explanation of the cell visualization problem I observe (VTK\_POLYHEDRON). I have generated VTU file with 3D mesh of polyhedrons using my own python script. Surface representation does not render accurately (see first figure bellow). However wireframe representation seems to be correct/reasonable (see second figure bellow). Is there any explanation for my observation or is there a better way to visualize such models/data?

 ![Representation: Surface](https://discourse.paraview.org/uploads/default/original/2X/9/990a84826f4c8de73c89913971eae7b18a13dcff.png)  
 ![Representation: Wireframe](https://discourse.paraview.org/uploads/default/original/2X/e/e56bf58f5bcbf634d8e759388ffe5eaab901e872.png)

Thank you!  
Pavel Jíška

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### Author: ![dcthomp](https://discourse.paraview.org/user_avatar/discourse.paraview.org/dcthomp/32/20_2.png) [@dcthomp](https://discourse.paraview.org/u/dcthomp)
#### Post date: [May 13, 2024, 12:02pm UTC](https://discourse.paraview.org/t/strange-display-representation-of-vtk-polyhedron-cells/14612/2 "2024-05-13T12:02:02Z")

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Note that concave polyhedra are not well-supported: [VTK: vtkPolyhedron Class Reference](https://vtk.org/doc/nightly/html/classvtkPolyhedron.html#Limitations)

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### Author: ![dcthomp](https://discourse.paraview.org/user_avatar/discourse.paraview.org/dcthomp/32/20_2.png) [@dcthomp](https://discourse.paraview.org/u/dcthomp)
#### Post date: [May 13, 2024, 12:15pm UTC](https://discourse.paraview.org/t/strange-display-representation-of-vtk-polyhedron-cells/14612/3 "2024-05-13T12:15:15Z")

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Also, it appears from your images that you are referring to [polygonal (2D)](https://vtk.org/doc/nightly/html/classvtkPolygon.html) rather than polyhedral (3D) cells. If that is the case, it seems like a bug in the triangulation method being used. Can you provide the dataset causing the problem? Because polygonal cells are intended to allow concavities, though not holes.

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### Author: ![Ieeshka](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/i/ec9cab/32.png) [@Ieeshka](https://discourse.paraview.org/u/Ieeshka)
#### Post date: [May 13, 2024, 12:23pm UTC](https://discourse.paraview.org/t/strange-display-representation-of-vtk-polyhedron-cells/14612/4 "2024-05-13T12:23:43Z")

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Actually this is 3D mesh visualized in 2D Interaction Mode. Here is the [VTU file](https://drive.google.com/file/d/1n0UAYoTKI8tKzAEf_hnIwZSrCCaGvbCe/view?usp=sharing). In general those cell are extruded polygons with concavities.

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### Author: ![Jeff\_Lee](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/j/8797f3/32.png) [@Jeff\_Lee](https://discourse.paraview.org/u/Jeff_Lee)
#### Post date: [June 24, 2026, 2:47pm UTC](https://discourse.paraview.org/t/strange-display-representation-of-vtk-polyhedron-cells/14612/5 "2026-06-24T14:47:28Z")

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Resurrecting this thread, vtk9.7 will have a fix for rendering of concave polygonal cells.