# A problem about surface smoothing
**URL:** https://discourse.vtk.org/t/a-problem-about-surface-smoothing/2011
**Category:** Support
**Created:** [October 31, 2019, 7:40am UTC](https://discourse.vtk.org/t/a-problem-about-surface-smoothing/2011 "2019-10-31T07:40:08Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@KeyboardMan](https://discourse.vtk.org/u/KeyboardMan)
#### Post date: [October 31, 2019, 7:40am UTC](https://discourse.vtk.org/t/a-problem-about-surface-smoothing/2011/1 "2019-10-31T07:40:08Z")
- I used vtkPolyDataBooleanFilter for Boolean operation
[vtkPolyDataBooleanFilter](https://github.com/zippy84/vtkbool)
- Before the Boolean operation
- This surface looks very smooth
- But after the Boolean operation
- Why is that? Is there a solution?
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### Author:  [@mwestphal](https://discourse.vtk.org/u/mwestphal)
#### Post date: [October 31, 2019, 8:03am UTC](https://discourse.vtk.org/t/a-problem-about-surface-smoothing/2011/2 "2019-10-31T08:03:50Z")
Looks like you are missing the normals in the process. You can add them back with vtkPolyDataNormals filter.
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### Author:  [@KeyboardMan](https://discourse.vtk.org/u/KeyboardMan)
#### Post date: [October 31, 2019, 8:42am UTC](https://discourse.vtk.org/t/a-problem-about-surface-smoothing/2011/3 "2019-10-31T08:42:57Z")
I still don’t get it. Can you be more specific?Or is there any documentation i can refer to?thank you
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### Author:  [@mwestphal](https://discourse.vtk.org/u/mwestphal)
#### Post date: [October 31, 2019, 8:51am UTC](https://discourse.vtk.org/t/a-problem-about-surface-smoothing/2011/4 "2019-10-31T08:51:42Z")
[https://vtk.org/doc/nightly/html/classvtkPolyDataNormals.html#details](https://vtk.org/doc/nightly/html/classvtkPolyDataNormals.html#details)
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### Author:  [@KeyboardMan](https://discourse.vtk.org/u/KeyboardMan)
#### Post date: [October 31, 2019, 8:57am UTC](https://discourse.vtk.org/t/a-problem-about-surface-smoothing/2011/5 "2019-10-31T08:57:18Z")
- Ok, thank you. This is very useful