# QuadricDecimation

VTKExamples/Cxx/Meshes/QuadricDecimation

### Description

This example uses Quadric Clustering, based on the work of Garland and Heckbert who first presented the quadric error measure at Siggraph '97 "Surface Simplification Using Quadric Error Metrics". For details of the algorithm Michael Garland's Ph.D. thesis is also recommended. Hughues Hoppe's Vis '99 paper, "New Quadric Metric for Simplifying Meshes with Appearance Attributes" is also a good take on the subject especially as it pertains to the error metric applied to attributes.

Seealso

QuadricClustering and Decimation.

### Code

QuadricDecimation.cxx

    #include <vtkVersion.h>
    #include <vtkPolyData.h>
    #include <vtkSphereSource.h>
    #include <vtkQuadricDecimation.h>
    #include <vtkXMLPolyDataReader.h>
    #include <vtkTriangleFilter.h>
    #include <vtkSmartPointer.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkProperty.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkRenderer.h>
    #include <vtkCamera.h>

    #include <vtkNamedColors.h>

    int main(int argc, char *argv[])
    {
      vtkSmartPointer<vtkPolyData> inputPolyData;
      if(argc > 1)
      {
        vtkSmartPointer<vtkXMLPolyDataReader> reader =
          vtkSmartPointer<vtkXMLPolyDataReader>::New();
        reader->SetFileName(argv[1]);
        vtkSmartPointer<vtkTriangleFilter> triangles =
          vtkSmartPointer<vtkTriangleFilter>::New();
        triangles->SetInputConnection(reader->GetOutputPort());
        triangles->Update();
        inputPolyData = triangles->GetOutput();
      }
      else
      {
        vtkSmartPointer<vtkSphereSource> sphereSource =
          vtkSmartPointer<vtkSphereSource>::New();
        sphereSource->SetThetaResolution(30);
        sphereSource->SetPhiResolution(15);
        sphereSource->Update();
        inputPolyData = sphereSource->GetOutput();
      }

      vtkSmartPointer<vtkNamedColors> colors =
        vtkSmartPointer<vtkNamedColors>::New();
      std::cout << "Before decimation" << std::endl << "------------" << std::endl;
      std::cout << "There are "
                << inputPolyData->GetNumberOfPoints() << " points." << std::endl;
      std::cout << "There are "
                << inputPolyData->GetNumberOfPolys() << " polygons." << std::endl;

      vtkSmartPointer<vtkQuadricDecimation> decimate =
        vtkSmartPointer<vtkQuadricDecimation>::New();
      decimate->SetInputData(inputPolyData);
      decimate->AttributeErrorMetricOn();
      decimate->SetTargetReduction(.9);
      decimate->VolumePreservationOn();

      decimate->Update();

      vtkSmartPointer<vtkPolyData> decimated =
        vtkSmartPointer<vtkPolyData>::New();
      decimated->ShallowCopy(decimate->GetOutput());

      std::cout << "After decimation" << std::endl << "------------" << std::endl;
      std::cout << "There are "
                << decimated->GetNumberOfPoints() << " points." << std::endl;
      std::cout << "There are "
                << decimated->GetNumberOfPolys() << " polygons." << std::endl;
      std::cout << "Reduction: " <<
        static_cast<double>((inputPolyData->GetNumberOfPolys() - decimated->GetNumberOfPolys())) /
        static_cast<double>(inputPolyData->GetNumberOfPolys()) << std::endl;

      vtkSmartPointer<vtkPolyDataMapper> inputMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      inputMapper->SetInputData(inputPolyData);

      vtkSmartPointer<vtkProperty> backFace =
        vtkSmartPointer<vtkProperty>::New();
      backFace->SetColor(colors->GetColor3d("gold").GetData());

      vtkSmartPointer<vtkActor> inputActor =
        vtkSmartPointer<vtkActor>::New();
      inputActor->SetMapper(inputMapper);
      inputActor->GetProperty()->SetInterpolationToFlat();
      inputActor->GetProperty()->SetColor(colors->GetColor3d("flesh").GetData());
      inputActor->SetBackfaceProperty(backFace);

      vtkSmartPointer<vtkPolyDataMapper> decimatedMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      decimatedMapper->SetInputData(decimated);

      vtkSmartPointer<vtkActor> decimatedActor =
        vtkSmartPointer<vtkActor>::New();
      decimatedActor->SetMapper(decimatedMapper);
      decimatedActor->GetProperty()->SetColor(colors->GetColor3d("flesh").GetData());
      decimatedActor->GetProperty()->SetInterpolationToFlat();
      decimatedActor->SetBackfaceProperty(backFace);

      // There will be one render window
      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->SetSize(600, 300);

      // And one interactor
      vtkSmartPointer<vtkRenderWindowInteractor> interactor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      interactor->SetRenderWindow(renderWindow);

      // Define viewport ranges
      // (xmin, ymin, xmax, ymax)
      double leftViewport[4] = {0.0, 0.0, 0.5, 1.0};
      double rightViewport[4] = {0.5, 0.0, 1.0, 1.0};

      // Setup both renderers
      vtkSmartPointer<vtkRenderer> leftRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderWindow->AddRenderer(leftRenderer);
      leftRenderer->SetViewport(leftViewport);
      leftRenderer->SetBackground(colors->GetColor3d("burlywood").GetData());

      vtkSmartPointer<vtkRenderer> rightRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderWindow->AddRenderer(rightRenderer);
      rightRenderer->SetViewport(rightViewport);
      rightRenderer->SetBackground(colors->GetColor3d("slate_grey").GetData());

      // Add the sphere to the left and the cube to the right
      leftRenderer->AddActor(inputActor);
      rightRenderer->AddActor(decimatedActor);

      // Shared camera looking down the -y axis
      vtkSmartPointer<vtkCamera> camera =
        vtkSmartPointer<vtkCamera>::New();
      camera->SetPosition (0, -1, 0);
      camera->SetFocalPoint (0, 0, 0);
      camera->SetViewUp (0, 0, 1);
      camera->Elevation(30);
      camera->Azimuth(30);

      leftRenderer->SetActiveCamera(camera);
      rightRenderer->SetActiveCamera(camera);

      leftRenderer->ResetCamera();
      leftRenderer->ResetCameraClippingRange();

      renderWindow->Render();
      interactor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(QuadricDecimation)

    find_package(VTK REQUIRED)
    include(${VTK_USE_FILE})

    add_executable(QuadricDecimation MACOSX_BUNDLE QuadricDecimation.cxx )

    target_link_libraries(QuadricDecimation ${VTK_LIBRARIES})

### Download and Build QuadricDecimation

Click here to download QuadricDecimation and its CMakeLists.txt file. Once the tarball QuadricDecimation.tar has been downloaded and extracted,

    cd QuadricDecimation/build

If VTK is installed:

    cmake ..

If VTK is not installed but compiled on your system, you will need to specify the path to your VTK build:

    cmake -DVTK_DIR:PATH=/home/me/vtk_build ..

Build the project:

    make

and run it:

    ./QuadricDecimation

WINDOWS USERS PLEASE NOTE: Be sure to add the VTK bin directory to your path. This will resolve the VTK dll's at run time.