[vtkusers] cleaning polydata precludes computing curvatures

vidyadhar vidyadhar at lucidindia.com
Tue Mar 31 00:07:42 EDT 2009

In all probability the cell and point normals are lost. 3DS meshes have both
and are imported by the importer. Clean may be removing them. Try using
vtkPolyDataNormals between clean and curvature. Set it up to compute both
point and cell normals. Compare the result with that for slices. It is
possible that vertex order in some cells gets changed in the pipeline (doubt
it) in which case enable auto-orient normals.

On Mon, Mar 30, 2009 at 10:16 PM, Lane Phillips <phillips at cs.umn.edu> wrote:

> I have a 3DS model and I want to do analysis of the surface curvature. I
> use a vtk3DSImporter to load the model and I notice that the model is sliced
> into multiple meshes, so I take the vtkPolyData from each mesh and send it
> through a vtkCurvatures and, magically, VTK displays the curvature as color
> on the surface, and I can spin the model at interactive rates.
> I don't want to deal with multiple meshes, so I add each vtkPolyData to a
> vtkAppendPolyData object, and send the output of that through the
> vtkCurvatures object.  VTK still displays the curvatures on the surface, but
> now it's extremely slow to rotate.  Maybe the slices cached better?
>  However, speed is not my concern right now...
> Now I have all the meshes in one vtkPolyData, but I assume they are not
> contiguous yet, so I run the output of the vtkAppendPolyData through a
> vtkCleanPolyData, hoping this will merge duplicate points and stitch the
> meshes together.  I send the output of vtkCleanPolyData through
> vtkCurvatures, but now the surface is rendered in one color.
> So my question is, what information is needed by vtkCurvatures that is
> getting destroyed by vtkCleanPolyData?
> I'm attaching my code; sorry it's a mess.  The important lines are 81
> through 127.
> Thanks,
> Lane
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