Get normals coordinates

Support
1

Hi VTK community,

Is there any options to get X,Y,Z coordinates of the cell normals?

Currently I have the following code:

normals = vtk.vtkPPolyDataNormals()
normals.SetInputConnection(decimate.GetOutputPort())

normals.ComputeCellNormalsOn()

normals.SplittingOff()
normals.FlipNormalsOff()
normals.ConsistencyOn()
normals.AutoOrientNormalsOn()
normals.Update()

For my further processing steps I need to get coordinates (ot at least angle of the normals). I’ve found vtkDeflectNormals() class, however, I get this error with it: AttributeError: module ‘vtkmodules.all’ has no attribute ‘vtkDeflectNormals’

1 Like
2

Normals are computed as float array and stored in cell data.

I don’t have the python code, in C++ one can do this

vtkFloatArray* normalsFloat = vtkFloatArray::SafeDownCast( polydata->GetCellData()->GetNormals() );
2 Likes
3

Thanks for your comment, I’ve tried your solution, however it works only with VTK primitives such as sphere, for example. When I use polydata->GetCellData()->GetNormals() with STL file, the result is None:

filename = “loop.STL”
source = vtk.vtkSTLReader()

source.SetFileName(filename)
source.Update()

polydata = vtk.vtkPolyData()
polydata.ShallowCopy(source.GetOutput())

normals = polydata.GetCellData().GetNormals()
print(normals)

The result as I mentioned is None. I’ve tried different STL files here, but the problem persists. Is there any problem with my code or GetNormals() works only with primitives?

4

Get the polydata from STL reader and compute the normal as you originally posted. If you don’t compute normal you cannot expect them to be there.

Cheers!

5

To generate points at the (parametric) center of cells use vtkCellCenters