[vtkusers] How to extract area weighted normals from cells?

[lynx.abraxas at freenet.de]

Hello!


Are the normals from vtkPolyDataNormals normalized?

I need a listing of surface area weighted normals of each cell of a
vtkPolyData mesh (from a smoothed marching cubes mesh).
Iterating now over all cells of this vtkPolyData I wonder how I can get the
associated cell normal and the cell area. I tried as follows but I'm
stuck. vtkCell has no getNormal() nor a getAtrribute("Quality") in which
the area is supposed to be after vtkMeshQuality().
Would it be better to extract all Normals and areas into arrays?
How would I have to calculate the weighted normals then?

    ##calc cell normal
    ##output as input but with normals added?

    triangleCellNormals= vtk.vtkPolyDataNormals()
    triangleCellNormals.SetInput(smoother.GetOutput())
    triangleCellNormals.ComputeCellNormalsOn()
    triangleCellNormals.ComputePointNormalsOff()
    triangleCellNormals.ConsistencyOn()
    triangleCellNormals.AutoOrientNormalsOn()
    triangleCellNormals.Update()


    ##calc cell area
    ##output as input but with areas added?

    triangleCellAN= vtk.vtkMeshQuality()
    triangleCellAN.SetInput(triangleCellNormals)
    triangleCellAN.SetTriangleQualityMeasureToArea()
    triangleCellAN.SaveCellQualityOn() ##default
    triangleCellAN.Update()



    for i in range(0, triangleCellAN.GetNumberOfCells()):

        cell= triangleCellAN.GetCell(i);
        cell.GetNormals()
        "Quality"


Thanks for any help or hints about this.
Lynx


On 17/12/09 09:09:03, David Doria wrote:
> On Thu, Dec 17, 2009 at 2:32 AM, Bryn Lloyd <blloyd at vision.ee.ethz.ch> wrote:
> > Another way to compute the area is via vtkMeshQuality.
> >
> > First pass the mesh through this filter, compute the area for all triangles
> > (SetTriangleQualityMeasureToArea()), and the obtain the values from the
> > vtkCellData in the output.
> >
> > Cheers
> > Bryn
> 
> Bryn,
> 
> I tried that:
> http://www.vtk.org/Wiki/VTK/Examples/Mesh_Quality
> 
> But the values in the "Quality" array are all 0. Any thoughts?
> 
> Thanks,
> 
> David
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