[vtkusers] vtkButterflySubdivisionFilter displays incorrect shape.

[madz]

I have a 3D contour plot which I'm plotting with several point values. To
give the image a more smoother interpolated look I applied the
vtkButterflySubdivisionFilter. However, after applying the filter, the shape
of the grid looks altered. I noticed that it renders a butterfly shape
(hence the name?) to the grid. The following is an example to highlight the
problem. 

#include <vtkSmartPointer.h>
#include <vtkActor.h>
#include <vtkDelaunay2D.h>
#include <vtkLookupTable.h>
#include <vtkMath.h>
#include <vtkPoints.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkCubeAxesActor.h>
#include <vtkInteractorStyleTrackballCamera.h>
#include <vtkCamera.h>
#include <vtkButterflySubdivisionFilter.h>

int main(int, char *[])
{
        // Create a grid of points (height/terrian map)
        vtkSmartPointer<vtkPoints> points =
                vtkSmartPointer<vtkPoints>::New();

        unsigned int GridSize = 5;
        double xx, yy, zz;

        points->InsertNextPoint(0, 0, 0.5);
        points->InsertNextPoint(0, 1, 0.5);
        points->InsertNextPoint(0, 2, 0.5);
        points->InsertNextPoint(1, 0, 0.5);
        points->InsertNextPoint(1, 1, 0.5);
        points->InsertNextPoint(1, 2, 0.5);
        points->InsertNextPoint(2, 0, 0.5);
        points->InsertNextPoint(2, 1, 0.5);
        points->InsertNextPoint(2, 2, 0.5);
        points->InsertNextPoint(3, 0, 0.5);
        points->InsertNextPoint(3, 1, 0.5);
        points->InsertNextPoint(3, 2, 0.5); 
       

        // Add the grid points to a polydata object
        vtkSmartPointer<vtkPolyData> inputPolyData =
vtkSmartPointer<vtkPolyData>::New();
        inputPolyData->SetPoints(points);

        // Triangulate the grid points
        vtkSmartPointer<vtkDelaunay2D> delaunay =
vtkSmartPointer<vtkDelaunay2D>::New();
#if VTK_MAJOR_VERSION <= 5
        delaunay->SetInput(inputPolyData);
#else
        delaunay->SetInputData(inputPolyData);
#endif
        delaunay->Update();
        vtkPolyData* outputPolyData = delaunay->GetOutput();

        double bounds[6];
        outputPolyData->GetBounds(bounds);

        // Find min and max z
        double minz = bounds[4];
        double maxz = bounds[5];

        // Create the color map
        vtkSmartPointer<vtkLookupTable> colorLookupTable =
                vtkSmartPointer<vtkLookupTable>::New();
        colorLookupTable->SetTableRange(minz, maxz);
        colorLookupTable->Build();

        // Generate the colors for each point based on the color map
        vtkSmartPointer<vtkUnsignedCharArray> colors =
vtkSmartPointer<vtkUnsignedCharArray>::New();
        colors->SetNumberOfComponents(3);
        colors->SetName("Colors");

        std::cout << "There are " << outputPolyData->GetNumberOfPoints()
                << " points." << std::endl;

        for(int i = 0; i < outputPolyData->GetNumberOfPoints(); i++)
        {
                double p[3];
                outputPolyData->GetPoint(i,p);

                double dcolor[3];
                colorLookupTable->GetColor(p[2], dcolor);
                unsigned char color[3];
                for(unsigned int j = 0; j < 3; j++)
                {
                        color[j] = static_cast<unsigned char>(255.0 *
dcolor[j]);
                }

                colors->InsertNextTupleValue(color);
        }

        outputPolyData->GetPointData()->SetScalars(colors);

        vtkSmartPointer<vtkCubeAxesActor> axes =
vtkSmartPointer<vtkCubeAxesActor>::New();
        axes->SetBounds(delaunay->GetOutput()->GetBounds());
        axes->SetFlyModeToOuterEdges();

        axes->XAxisMinorTickVisibilityOff();
        axes->YAxisMinorTickVisibilityOff();
        axes->ZAxisMinorTickVisibilityOff();
        axes->SetXLabelFormat("%6.1f");


 vtkSmartPointer<vtkButterflySubdivisionFilter> subdivide =
vtkSmartPointer<vtkButterflySubdivisionFilter>::New();
  subdivide->SetNumberOfSubdivisions(3);
#if VTK_MAJOR_VERSION <= 5
  subdivide->SetInputConnection(outputPolyData->GetProducerPort());
#else
  subdivide->SetInputData(outputPolyData);
#endif

  // Create a mapper and actor
  vtkSmartPointer<vtkPolyDataMapper> mapper =
vtkSmartPointer<vtkPolyDataMapper>::New();
  mapper->SetInputConnection(subdivide->GetOutputPort());

  vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
        actor->SetMapper(mapper);

        // 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();
        renderWindowInteractor->SetRenderWindow(renderWindow);

        //prevents the pointer option from going haywire
        vtkSmartPointer<vtkInteractorStyleTrackballCamera> style =
vtkSmartPointer<vtkInteractorStyleTrackballCamera>::New();
        renderWindowInteractor->SetInteractorStyle(style);

        // Add the actor to the scene
        renderer->AddActor(actor);
        renderer->SetBackground(.1, .2, .3);

        // Render and interact
        renderWindow->Render();

        renderer->GetActiveCamera()->Elevation(290);
        renderer->AddViewProp(axes);
        axes->SetCamera(renderer->GetActiveCamera());

        renderWindowInteractor->Start();

        return EXIT_SUCCESS;
}

As you can see in the following image the maximum point values of the shape
is altered, I don't want those values altered in my plot. How do I avoid it.


Normal image without subdivision and with ButterflySubdivision. 

<http://vtk.1045678.n5.nabble.com/file/n5724768/rect.png>    
<http://vtk.1045678.n5.nabble.com/file/n5724768/butter_rect.png>  


Thank you. 



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