[vtkusers] vtkButterflySubdivisionFilter displays incorrect shape.

[Bill Lorensen]

Although the the surface will pass through the original points,
evaluated positions between the points might overshoot. This is the
nature of smooth interpolation.

You can use LinearSubdivisionFilter, which  wiki produce more
triangles, the the resulting surface will not be smooth.

On Mon, Dec 2, 2013 at 3:49 AM, madz <madaramh at gmail.com> wrote:
> 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.
>
>
>
> --
> View this message in context: http://vtk.1045678.n5.nabble.com/vtkButterflySubdivisionFilter-displays-incorrect-shape-tp5724768.html
> Sent from the VTK - Users mailing list archive at Nabble.com.
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