[vtkusers] Problem with two polydata clip

[minyang]

This is VTK 5.10.1.

Requirement:
User pick several points on the screen, create a closed polygon, then cut
the below mesh(polydata) with this polygon.

Implement:
Extrude the polygon, triangulate it and clip mesh

Core Codes:

        vtkSmartPointer<vtkPolyData> polyData = 
vtkSmartPointer<vtkPolyData>::New();
        polyData->SetPoints(polyLinePoints);
	polyData->SetPolys(polygons);

	vtkSmartPointer<vtkLinearExtrusionFilter> extrude =
vtkSmartPointer<vtkLinearExtrusionFilter>::New();
	extrude->SetInput(polyData);
	extrude->SetExtrusionTypeToNormalExtrusion();
	extrude->CappingOn();
	extrude->SetVector(0, 0, -1 );
	extrude->SetScaleFactor (50);
	extrude->Update();

	vtkSmartPointer<vtkTriangleFilter> tria =
vtkSmartPointer<vtkTriangleFilter>::New();
	tria->SetInputConnection(extrude->GetOutputPort());
	tria->Update();

	vtkSmartPointer<vtkPolyDataNormals> norm =
vtkSmartPointer<vtkPolyDataNormals>::New();
	norm->SetInput(tria->GetOutput());

	vtkSmartPointer<vtkImplicitPolyDataDistance> implicit_data =
vtkSmartPointer<vtkImplicitPolyDataDistance>::New();
	implicit_data->SetInput(norm->GetOutput());

	vtkSmartPointer<vtkClipPolyData> clipper =
vtkSmartPointer<vtkClipPolyData>::New();
	clipper->SetInput(inputMeshPolyData);
	clipper->SetClipFunction(implicit_data); 
	clipper->GenerateClippedOutputOn();
	clipper->InsideOutOn();
	clipper->Update();
	
	poly_data_copy = vtkPolyData::New();
	poly_data_copy->DeepCopy(clipper->GetOutput()/*cutter->GetOutput()*/);

	vtkSmartPointer<vtkPolyDataMapper> mapper_cut =
vtkSmartPointer<vtkPolyDataMapper>::New();
	mapper_cut->SetInput(poly_data_copy);
	vtkSmartPointer<vtkActor> actor_copy = vtkSmartPointer<vtkActor>::New();
	actor_copy->SetMapper(mapper_cut);
	actor_copy->VisibilityOn();
	renderer->AddActor(actor_copy);
	renderWindow->Render();
<http://vtk.1045678.n5.nabble.com/file/n5734644/clip_issue.png> 

Problem: In red circle, there are additional meshes clipped near the acute
angle. These section should not be clipped. Any expert know what wrong of my
codes? or is there any limition of  VTK in handle two polygon clip? Thanks
in advance.



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