# Zooming in on the surface results in stripes

**URL:** <https://discourse.vtk.org/t/zooming-in-on-the-surface-results-in-stripes/12133>\
**Category:** Development\
**Tags:** code\
**Created:** [August 11, 2023, 4:14am UTC](https://discourse.vtk.org/t/zooming-in-on-the-surface-results-in-stripes/12133 "2023-08-11T04:14:09Z")\
**Posts on this page:** 1\
**Showing post:** 10

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**Author:** ![whereismymoney](https://discourse.vtk.org/user_avatar/discourse.vtk.org/whereismymoney/32/6859_2.png) [@whereismymoney](https://discourse.vtk.org/u/whereismymoney)\
**Post date:** [August 29, 2023, 2:50am UTC](https://discourse.vtk.org/t/zooming-in-on-the-surface-results-in-stripes/12133/10 "2023-08-29T02:50:41Z")

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It is important to compute point normals, not just cell normals.  
Without the point normals the behavior is bad and the renderer may crash on some systems.  
I provided an example here

> [@vtkPolyDataNormals appears to behave incorrectly](https://discourse.vtk.org/t/vtkpolydatanormals-appears-to-behave-incorrectly/11988):
>
> The sample code I provide here allows you to easily compare SetComputePointNormals(true) and SetComputePointNormals(false), so we can compare the correct behavior with the incorrect behavior, shown in this image: Here is the code: #include \<vtkActor.h\> #include \<vtkNew.h\> #include \<vtkRenderWindow.h\> #include \<vtkRenderWindowInteractor.h\> #include \<vtkRenderer.h\> #include \<vtkPolyDataNormals.h\> #include \<vtkPolyDataReader.h\> #include \<vtkPolyDataMapper.h\> #include \<vtkCleanPolyData.h\>…

This lets you compare SetComputePointNormals(true) and SetComputePointNormals(false).  
-Matthias

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