Efficient use of vtkPolyDataNormals to show smooth surfaces

Support
1

Hi,

I am using vtkLookupTable() and vtkUnsignedCharArray() to re-color a mesh. The Array that contains the colors is modified several times interactively. The problem I have is that to show the actor with a smooth surface I am using vtkPolyDataNormals, as shown below, but I have to create vtkPolydataNormals() everytime I need to recolor the actor. I can create the mapper only once and modify it but it has not been possible to do the same with the vtkPolydataNormals().
Is there a way to achieve a smooth surface in an efficient manner?

def Recolor_Actor(self, mesh):
        normals = vtkPolyDataNormals()
        normals.SetInputData(mesh)
        normals.SetFeatureAngle(80)
        normals.AutoOrientNormalsOn()
        normals.Update()
        self.mapper.SetInputData(normals.GetOutput())
        self.mapper.ScalarVisibilityOn()
        actor.SetMapper(self.mapper)

Thanks!

2

Re-applying vtkPolyDataNormals shouldn’t be necessary. Can you show the code where you apply the lookup table?

3

Hi, thank you for you reply, this in an example of where I apply the lookup table:

        lut = self.CreateLUTtable(self.min, self.max)

        self.colors_init.SetNumberOfComponents(3)
        self.colors_init.Fill(255)

        for h in range(self.radius_list.GetNumberOfIds()):
            dcolor = 3 * [0.0]
            index_id = self.radius_list.GetId(h)
            lut.GetColor(self.efieldnorms[index_id], dcolor)
            color = 3 * [0.0]
            for j in range(0, 3):
                color[j] = int(255.0 * dcolor[j])
            self.colors_init.InsertTuple(index_id, color)
        mesh.GetPointData().SetScalars(self.colors_init)
        self.Recolor_Actor(mesh)
4

You can apply the lookup table with the mapper instead of changing the mesh dataset:

mapper.SetLookupTable(lut)
mapper.SetScalarRange(self.min, self.max)

Changing the appearance of the dataset via the mapper and/or actor is always more efficient than modifying the dataset itself. Modifying the dataset always requires that downstream filters have to re-execute.

To be more clear, what I’m saying is that the mesh scalars should be the efieldnorms, not the colors. The coloring can be applied (very efficiently) by the mapper.

5

Hi,

Ok thank you! I will look into it. I just found examples using the LUT this way, since I am just coloring a circle that moves interactively on the surface of the mesh.

6

The mapper applies the LUT to the whole mesh, not just part of the mesh. So if you’re only recoloring part of the mesh, then what I suggested will not work.

Instead, you can generate the normals before recoloring the mesh, instead of after. The vtkPolyDataNormals filter can be used on meshes that have no scalars.

7

Ok, thank you very much!