# Incorrect rendering of polydata surfaces when using vtkActor::SetUserTransform

**URL:** https://discourse.vtk.org/t/incorrect-rendering-of-polydata-surfaces-when-using-vtkactor-setusertransform/12196
**Category:** Support
**Created:** [August 24, 2023, 8:13am UTC](https://discourse.vtk.org/t/incorrect-rendering-of-polydata-surfaces-when-using-vtkactor-setusertransform/12196 "2023-08-24T08:13:03Z")
**Posts on this page:** 1
**Showing post:** 2

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### Author: ![dyollb](https://discourse.vtk.org/user_avatar/discourse.vtk.org/dyollb/32/7649_2.png) [@dyollb](https://discourse.vtk.org/u/dyollb)
#### Post date: [August 25, 2023, 5:11am UTC](https://discourse.vtk.org/t/incorrect-rendering-of-polydata-surfaces-when-using-vtkactor-setusertransform/12196/2 "2023-08-25T05:11:23Z")

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Okay. It looks like the same issue was discussed here: [mirroring and normals](https://discourse.vtk.org/t/mirroring-and-normals/2767)

I will see if normals are the problem.  
Update: disabling normal computation fixed the issue. I guess I can use vtkReverseSense and flip normals if the matrix has a negative determinant.

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_[View the full topic](https://discourse.vtk.org/t/incorrect-rendering-of-polydata-surfaces-when-using-vtkactor-setusertransform/12196)._