[vtkusers] vtkUnstructuredGrid and Gouraud Shading

[Ken Martin]

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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Ken Martin PhD
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