[vtkusers] vtkImplicitLoop and vtkExtractPolyDataGeometry

[NsPx]

Hi all,

I am coding a tools to interactively select a region of a mesh with 
vtkContourWidget.

To get this contour, I headed for vtkExtractPolyDataGeometry and 
vtkImplicitLoop.

Now I don't understand very well what happened : most of the time I get 
extra cells which doesn't belong to the interior of the contour.
For example here : 
http://img341.imageshack.us/img341/523/sanstitreypg.jpg, I get the 
desired region + the back face of this region.

Can someone explain me what's wrong with this code ?

// 1. close the loop if not
vtkContourWidget->CloseLoop();

// 2. get the contour as a polydata
vtkContourRepresentation *contourRep = 
reinterpret_cast<vtkContourRepresentation*>(vtkContourWidget->WidgetRep);

vtkSmartPointer<vtkPoints> selectionPoints = 
vtkSmartPointer<vtkPoints>::New();
selectionPoints = 
contourRep->GetContourRepresentationAsPolyData()->GetPoints();


// 3. Pass convert the contour into vtkImplicitSelectionLoop
vtkSmartPointer<vtkImplicitSelectionLoop> loop = 
vtkSmartPointer<vtkImplicitSelectionLoop>::New();
loop->SetLoop(selectionPoints);

// 4. clip mesh with the contour
vtkSmartPointer<vtkExtractPolyDataGeometry> clip = 
vtkSmartPointer<vtkExtractPolyDataGeometry>::New();
clip->SetImplicitFunction(loop);
clip->SetInput(mesh);
clip->SetExtractInside(1);
clip->SetExtractBoundaryCells(1);
clip->Update();

Thanks by advance
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