# How to render coincident cells?

**URL:** https://discourse.vtk.org/t/how-to-render-coincident-cells/16516
**Category:** Support
**Created:** [August 19, 2026, 4:25pm UTC](https://discourse.vtk.org/t/how-to-render-coincident-cells/16516 "2026-08-19T16:25:57Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![raungst](https://discourse.vtk.org/user_avatar/discourse.vtk.org/raungst/32/1965_2.png) [@raungst](https://discourse.vtk.org/u/raungst)
#### Post date: [August 19, 2026, 4:25pm UTC](https://discourse.vtk.org/t/how-to-render-coincident-cells/16516/1 "2026-08-19T16:25:57Z")

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I sometimes have coincident cells in the same unstructured grid / actor. My problem is that neither one of them renders when this happens. If I hide one of them, the other one shows up. I’ve tried both SetResolveCoincidentTopologyToPolygonOffset and SetRelativeCoincidentTopologyPolygonOffsetParameters but haven’t been able to get them to not disappear.

Is there any other setting or approach that would work?

Thanks!

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### Author: ![sankhesh](https://discourse.vtk.org/user_avatar/discourse.vtk.org/sankhesh/32/73_2.png) [@sankhesh](https://discourse.vtk.org/u/sankhesh)
#### Post date: [September 11, 2026, 7:11pm UTC](https://discourse.vtk.org/t/how-to-render-coincident-cells/16516/2 "2026-09-11T19:11:51Z")

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Thanks for the details! Could you share a small code snippet showing how you create the unstructured grid and actor, along with the exact calls and parameter values you tried for `SetResolveCoincidentTopologyToPolygonOffset` and `SetRelativeCoincidentTopologyPolygonOffsetParameters`?

It would also help to know which VTK version and rendering backend you’re using.

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### Author: ![raungst](https://discourse.vtk.org/user_avatar/discourse.vtk.org/raungst/32/1965_2.png) [@raungst](https://discourse.vtk.org/u/raungst)
#### Post date: [September 16, 2026, 3:15pm UTC](https://discourse.vtk.org/t/how-to-render-coincident-cells/16516/3 "2026-09-16T15:15:03Z")

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Here’s an example file. It has two hexes on top of each other. As is, nothing shows up. If you comment one of them out, you see it as expected. No values of the resolving coincident topology parameters seem to change anything for me when the two are coincident.

Thanks!

[coincident.py](https://discourse.vtk.org/uploads/short-url/6x4YiIXkqB8fOpqfWlaMRM4Bht3.py) (2.3 KB)