[vtkusers] get only normals from extracted surface

[Johannes Holzmeister]

Hi!

I extracted a surface with "vtkExtractPolyDataGeometry". Now I want to get the normals of the extracted surface, then I would like to add up the vectors and get a main vector. 
But how can I only get the Normals of the points which are insinde or at the surface? 
If I try "vtkPolyDataNormals" I get the normals of every single point of the image not only the normals of the surfacepoints.


code:
vtkExtractPolyDataGeometry* extract = vtkExtractPolyDataGeometry::New();

extract->SetInput(objectContainer4);

extract->SetImplicitFunction(plane);

extract->ExtractInsideOff();

extract->ExtractBoundaryCellsOn();

extract->Update();

 

vtkExtractPolyDataGeometry* extract1 = vtkExtractPolyDataGeometry::New();

extract1->SetInput(extract->GetOutput());

extract1->SetImplicitFunction(plane);

extract1->ExtractInsideOn();

extract1->ExtractBoundaryCellsOn();

extract1->Update();



vtkPolyDataNormals* norm = vtkPolyDataNormals::New();

norm->SetInput(extract1->GetOutput());

norm->Update();



Thank you for your help!!
Johannes
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