[vtkusers] vtkUnstructuredGrid and Gouraud Shading

Luca Pallozzi Lavorante lplavorante at gmail.com
Tue Nov 29 10:05:34 EST 2016

Hi Ken, thank you very much for your reply. I will follow the suggested


On Tue, Nov 29, 2016 at 12:33 PM, Ken Martin <ken.martin at kitware.com> wrote:

> You need normals for smooth shading. So yes, something like
> vtkUnstructuredGrid -> vtkGeometryFilter (with merging on) ->
> vtkPolyDataNormals
> Do you have to convert to polydata? Technically no, you could volume
> render the 3D cells using ProjectedTetrahedra but the most common approach
> is to extract some sort of polygonal surface and render that.
> On Tue, Nov 29, 2016 at 6:57 AM, Luca Pallozzi Lavorante <
> lplavorante at gmail.com> wrote:
>> Hi  vtkusers,
>> how can I display a vtkUnstructuredGrid using Gouraud shading? I have
>> seen two or three similar posts on the list but was unable to find any
>> answer.
>> I have an unstructured grid with ~50000 3D cells (Triquadratic
>> Hexahedra). I need to extract its outer shape and visualize it with a
>> smooth appearance. I verified that the method vtkActor::GetProperty()->SetInterpolationToGouraud()
>> is of no avail on an actor built directly from the grid's vtkDataSetMapper.
>> So I though I should convert the unstructured grid to a polygonal
>> representation in order to compute normals on it using vtkPolyDataNormals.
>> Here I have another doubt. I want to extract just the boundary faces from
>> the unstructured grid (something I have successfully done using a
>> vtkDataSetSurfaceFilter fed with a vtkStructuredGrid).
>> Which is the proper pipeline I should follow?
>> vtkUnstructuredGrid -> vtkDataSetSurfaceFilter -> vtkPolyDataNormals ?
>> Is vtkDataSetSurfaceFilter able to extract only the boundary faces from
>> an unstructured grid?
>> Also, is the polygonal conversion strictly necessary? I ask this because
>> this is probably computationally costly.
>>  Thank you in advance for any help,
>>           Luca
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