# Decimation

VTKExamples/Cxx/Meshes/Decimation

### Description

This example decimates a mesh. The SetTargetReduction function specifies how many triangles should reduced by specifying the percentage (0,1) of triangles to be removed. For example, if the mesh contains 100 triangles and SetTargetReduction(.90) is called, after the decimation there will be approximately 10 triangles - a 90% reduction.

### Code

Decimation.cxx

    #include <vtkVersion.h>
    #include <vtkPolyData.h>
    #include <vtkSphereSource.h>
    #include <vtkDecimatePro.h>
    #include <vtkSmartPointer.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkProperty.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkRenderer.h>

    int main(int, char *[])
    {
      vtkSmartPointer<vtkSphereSource> sphereSource =
        vtkSmartPointer<vtkSphereSource>::New();
      sphereSource->Update();

      vtkSmartPointer<vtkPolyData> input =
        vtkSmartPointer<vtkPolyData>::New();
      input->ShallowCopy(sphereSource->GetOutput());

      std::cout << "Before decimation" << std::endl << "------------" << std::endl;
      std::cout << "There are " << input->GetNumberOfPoints() << " points." << std::endl;
      std::cout << "There are " << input->GetNumberOfPolys() << " polygons." << std::endl;

      vtkSmartPointer<vtkDecimatePro> decimate =
        vtkSmartPointer<vtkDecimatePro>::New();
    #if VTK_MAJOR_VERSION <= 5
      decimate->SetInputConnection(input->GetProducerPort());
    #else
      decimate->SetInputData(input);
    #endif
      //decimate->SetTargetReduction(.99); //99% reduction (if there was 100 triangles, now there will be 1)
      decimate->SetTargetReduction(.10); //10% reduction (if there was 100 triangles, now there will be 90)
      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;

      vtkSmartPointer<vtkPolyDataMapper> inputMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
    #if VTK_MAJOR_VERSION <= 5
      inputMapper->SetInputConnection(input->GetProducerPort());
    #else
      inputMapper->SetInputData(input);
    #endif
      vtkSmartPointer<vtkActor> inputActor =
        vtkSmartPointer<vtkActor>::New();
      inputActor->SetMapper(inputMapper);

      vtkSmartPointer<vtkPolyDataMapper> decimatedMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
    #if VTK_MAJOR_VERSION <= 5
      decimatedMapper->SetInputConnection(decimated->GetProducerPort());
    #else
      decimatedMapper->SetInputData(decimated);
    #endif
      vtkSmartPointer<vtkActor> decimatedActor =
        vtkSmartPointer<vtkActor>::New();
      decimatedActor->SetMapper(decimatedMapper);

      // 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(.6, .5, .4);

      vtkSmartPointer<vtkRenderer> rightRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderWindow->AddRenderer(rightRenderer);
      rightRenderer->SetViewport(rightViewport);
      rightRenderer->SetBackground(.4, .5, .6);

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

      leftRenderer->ResetCamera();

      rightRenderer->ResetCamera();

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

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(Decimation)

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

    add_executable(Decimation MACOSX_BUNDLE Decimation.cxx)

    target_link_libraries(Decimation ${VTK_LIBRARIES})

### Download and Build Decimation

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

    cd Decimation/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:

    ./Decimation

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.