[vtkusers] Rendering/Computing normals of a surface

[Bill Lorensen]

How are you creating your Kinect mesh?


On Fri, Apr 12, 2013 at 8:28 AM, Kilgus, Thomas <t.kilgus at dkfz-heidelberg.de
> wrote:

> Hi everyone,****
>
> ** **
>
> I’m trying to compute and render normals of certain vertices of a mesh (in
> fact a Kinect mesh). I assume that I have to compute the normals via
> vtkPolyDataNormals and display them using a vtkGlyph3d? ****
>
> ** **
>
> I observed some strange behavior which really confused me:****
>
> ** **
>
> **1.       **If I create a vtkPlaneSource or load a ball from hard disc
> and compute normals for that data, everything seems fine. If I load an
> “open” surface (my Kinect mesh), there are no normals displayed. The
> documentation says that SetAutoOrientNormals does only work with closed
> surfaces. But at the moment I don’t care about orientation. There should be
> normals for at least some vertices of an open mesh, shouldn’t there?****
>
> **2.       **If I load my Kinect mesh and make a new polydata which
> contains as much points at (0,0,0) as I have normals and set the normals
> for the new polydata, the glyph will produce arrows pointing from (0,0,0)
> to somewhere. This looks pretty good could but could be a random result
> with empty memory. ****
>
> **3.       **If I connect my vtkPlaneSource or the ball directly to the
> glyph (I skip the vtkPolyDataNormals), normals are still rendered
> correctly. Does this mean my vtkPlaneSource already contains them from the
> beginning? Are they computed in the background somewhere inside the
> glyph3d? Is the vtkPolyDataNormals even necessary? This only works for the
> plane and the ball - not for the Kinect mesh. I can imagine that a plane
> automatically computes its normal on Update(), but why does my ball have
> normals already?****
>
> **4.       **How can I get the normal of a certain vertex Id? If I use
> vtkFloatArray::SafeDownCast(output->GetPointData()->GetNormals()) are Id’s
> equal to the vertex Id’s of the polydata? What happens if I turn splitting
> on and get multiple normals for each vertex? How is the mapping done?****
>
> ** **
>
> My code looks as follows:****
>
> ** **
>
> vtkSmartPointer<vtkPolyData> inputPolyData = //load some data****
>
> ** **
>
>   // Generate normals****
>
>   vtkSmartPointer<vtkPolyDataNormals> normalGenerator =
> vtkSmartPointer<vtkPolyDataNormals>::New();****
>
>   normalGenerator->SetInput( inputPolyData );****
>
>   normalGenerator->ComputePointNormalsOn();****
>
>   normalGenerator->ComputeCellNormalsOff();****
>
>   normalGenerator->SetSplitting(0); //I want exactly one normal per vertex
> ****
>
>   normalGenerator->Update();****
>
> ** **
>
>   vtkSmartPointer<vtkPolyDataMapper> mapperNormals =****
>
>       vtkSmartPointer<vtkPolyDataMapper>::New();****
>
> ** **
>
>   //I chose arrows as representation****
>
>   vtkSmartPointer<vtkArrowSource> arrow =
> vtkSmartPointer<vtkArrowSource>::New();****
>
>   arrow->Update();****
>
> ** **
>
> //use the output of vtkPolyDataNormals as input for the glyph3d****
>
> vtkSmartPointer<vtkGlyph3D> glyph =
> vtkSmartPointer<vtkMaskedGlyph3D>::New();****
>
>   glyph->SetInput( normalGenerator->GetOutput() );****
>
>   glyph->SetSourceConnection(arrow->GetOutputPort());****
>
>   glyph->OrientOn();****
>
>   glyph->SetVectorModeToUseNormal();****
>
>   glyph->Update();****
>
> ** **
>
>   mapperNormals->SetInputConnection(glyph->GetOutputPort());****
>
> ** **
>
> //now follows standard code which could be taken from almost any example…*
> ***
>
>   vtkSmartPointer<vtkActor> actorNormals =****
>
>       vtkSmartPointer<vtkActor>::New();****
>
>   actorNormals->SetMapper(mapperNormals);****
>
> ** **
>
>   // Create a renderer, render window, and interactor****
>
>   vtkSmartPointer<vtkRenderer> renderer =****
>
>       vtkSmartPointer<vtkRenderer>::New();****
>
>   vtkSmartPointer<vtkRenderWindow> renderWindow =****
>
>       vtkSmartPointer<vtkRenderWindow>::New();****
>
>   renderWindow->AddRenderer(renderer);****
>
>   vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =****
>
>       vtkSmartPointer<vtkRenderWindowInteractor>::New();****
>
>   vtkSmartPointer<vtkInteractorStyleTrackballCamera> style =
> vtkSmartPointer<vtkInteractorStyleTrackballCamera>::New();****
>
>   renderWindowInteractor->SetInteractorStyle(style);****
>
>   renderWindowInteractor->SetRenderWindow(renderWindow);****
>
> ** **
>
>   // Add the actor to the scene****
>
>   renderer->AddActor(actorNormals);****
>
> ** **
>
>   // Render and interact****
>
>   renderWindow->Render();****
>
>   renderWindowInteractor->Start();****
>
> ** **
>
> Regards,****
>
> Thomas****
>
> ** **
>
> ** **
>
> Thomas Kilgus****
>
> German Cancer Research Center (DKFZ)****
>
> Div. Medical and Biological Informatics ****
>
> Junior group: Computer-assisted Interventions (E131)****
>
> Im Neuenheimer Feld 280****
>
> 69120 Heidelberg, Germany****
>
> Phone: +49(0) 6221-42-3545****
>
> ** **
>
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-- 
Unpaid intern in BillsBasement at noware dot com
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