# Why would \`vtkPolyDataNormals\` change the number of nodes?
**URL:** https://discourse.vtk.org/t/why-would-vtkpolydatanormals-change-the-number-of-nodes/12458
**Category:** Support
**Created:** [October 9, 2023, 8:10pm UTC](https://discourse.vtk.org/t/why-would-vtkpolydatanormals-change-the-number-of-nodes/12458 "2023-10-09T20:10:57Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@rexthor](https://discourse.vtk.org/u/rexthor)
#### Post date: [October 9, 2023, 8:10pm UTC](https://discourse.vtk.org/t/why-would-vtkpolydatanormals-change-the-number-of-nodes/12458/1 "2023-10-09T20:10:57Z")
I have a `*.vtp` file that does not have normals (but needs them for what I am doing next). I wanted to use `vtkPolyDataNormals` to add them … but it changes the number of nodes??
```python
rd = vtk.vtkXMLPolyDataReader()
rd.SetFileName("input.vtp")
rd.Update()
pd = rd.GetOutput()
print(pd.GetNumberOfPoints())
104923
nf = vtk.vtkPolyDataNormals()
nf.SetInputData(pd)
nf.Update()
print(nf.GetOutput().GetPointData().GetNormals().GetNumberOfTuples())
104670
```
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### Author:  [@Christos\_Tsolakis](https://discourse.vtk.org/u/Christos_Tsolakis)
#### Post date: [October 9, 2023, 8:33pm UTC](https://discourse.vtk.org/t/why-would-vtkpolydatanormals-change-the-number-of-nodes/12458/2 "2023-10-09T20:33:20Z")
From `vtkPolyDataNormals` [documentation](https://vtk.org/doc/nightly/html/classvtkPolyDataNormals.html#details)
> The filter can reorder polygons to ensure consistent orientation across polygon neighbors. Sharp edges can be split and **points duplicated** with separate normals to give crisp (rendered) surface definition. It is also possible to globally flip the normal orientation.
Experiment with _Splitting_ property as well as the _FeatureAngle_
---
### Author:  [@rexthor](https://discourse.vtk.org/u/rexthor)
#### Post date: [October 9, 2023, 8:57pm UTC](https://discourse.vtk.org/t/why-would-vtkpolydatanormals-change-the-number-of-nodes/12458/3 "2023-10-09T20:57:55Z")
Ah, forgot that, thanks