[vtkusers] Is Normal Estimation of the Point Set an ill-posed problem?

[David Doria]

> I have tried vtkPolyDataNormals, vtkPointSetNormalEstimation to get the
> normals,

vtkPolyDataNormals is not intended to estimate normals of a point cloud.

> but both functions gave me wrong output.

What do you mean "wrong output"? vtkPointSetNormalEstimation will give
you unoriented normals - that is, no guarantee that the normals are
all facing "out". Did you follow vtkPointSetNormalEstimation with
vtkPointSetNormalOrientation?

> Are there any other ways to estimate normals of the point set?

Not in VTK. PCL (pointclouds.org) has implemented the same method that
we implemented in the
vtkPointSetNormalEstimation/vtkPointSetNormalOrientation pair, maybe
you'll have better luck with theirs?

> Or, is the normal estimation of the point set an ill-posed problem?

Definitely.

> Ps. When I tried to use vtkPointSetNormalEstimation, I missed a chance to
> say thank to David Doria.
>
> Your advices were very helpful and I figured out what the problem was.

No problem at all.

David