# PolyDataConnectivityFilter LargestRegion

VTKExamples/Cxx/PolyData/PolyDataConnectivityFilter_LargestRegion

### Description

This example uses vtkPolyDataConnectivityFilter to keep the largest connected region of a mesh. Note that this is based on the number of points, not the actual area of the region.

The original vtkPolyData is red, on top. The extracted region is yellow, on the bottom.

Note

Contrast this with PolyDataConnectivityFilter_SpecifiedRegion.

Note

Contributed by: Jinyoung Hwang

### Code

PolyDataConnectivityFilter_LargestRegion.cxx

    #include <vtkSmartPointer.h>
    #include <vtkPolyDataConnectivityFilter.h>

    #include <vtkSphereSource.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkActor.h>
    #include <vtkProperty.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkAppendPolyData.h>

    #include <vtkNamedColors.h>

    int main(int, char *[])
    {
      vtkSmartPointer<vtkNamedColors> colors =
        vtkSmartPointer<vtkNamedColors>::New();

      // Small sphere
      vtkSmartPointer<vtkSphereSource> sphereSource1 =
        vtkSmartPointer<vtkSphereSource>::New();
      sphereSource1->SetRadius(5);

      // Large sphere
      vtkSmartPointer<vtkSphereSource> sphereSource2 =
        vtkSmartPointer<vtkSphereSource>::New();
      sphereSource2->SetRadius(10);
      sphereSource2->SetCenter(25,0,0);
      sphereSource2->SetThetaResolution(10);
      sphereSource2->SetPhiResolution(10);

      vtkSmartPointer<vtkAppendPolyData> appendFilter =
        vtkSmartPointer<vtkAppendPolyData>::New();
      appendFilter->AddInputConnection(sphereSource1->GetOutputPort());
      appendFilter->AddInputConnection(sphereSource2->GetOutputPort());

      vtkSmartPointer<vtkPolyDataConnectivityFilter> connectivityFilter =
        vtkSmartPointer<vtkPolyDataConnectivityFilter>::New();
      connectivityFilter->SetInputConnection(appendFilter->GetOutputPort());
      connectivityFilter->SetExtractionModeToLargestRegion();

      // Create a mapper and actor for original data
      vtkSmartPointer<vtkPolyDataMapper> originalMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      originalMapper->SetInputConnection(appendFilter->GetOutputPort());

      vtkSmartPointer<vtkActor> originalActor =
        vtkSmartPointer<vtkActor>::New();
      originalActor->SetMapper(originalMapper);
      originalActor->GetProperty()->SetColor(colors->GetColor3d("Tomato").GetData());

      // Create a mapper and actor for extracted data
      vtkSmartPointer<vtkPolyDataMapper> extractedMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      extractedMapper->SetInputConnection(connectivityFilter->GetOutputPort());
      extractedMapper->Update();

      vtkSmartPointer<vtkActor> extractedActor =
        vtkSmartPointer<vtkActor>::New();
      extractedActor->GetProperty()->SetColor(colors->GetColor3d("Banana").GetData());
      extractedActor->SetMapper(extractedMapper);
      extractedActor->SetPosition(0,-20,0);

      // Visualization
      vtkSmartPointer<vtkRenderer> renderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderer->AddActor(originalActor);
      renderer->AddActor(extractedActor);
      renderer->GradientBackgroundOn();
      renderer->SetBackground (colors->GetColor3d("Gold").GetData());
      renderer->SetBackground2 (colors->GetColor3d("Silver").GetData());

      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->AddRenderer(renderer);

      vtkSmartPointer<vtkRenderWindowInteractor> interactor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      interactor->SetRenderWindow(renderWindow);
      interactor->Initialize();
      interactor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(PolyDataConnectivityFilter_LargestRegion)

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

    add_executable(PolyDataConnectivityFilter_LargestRegion MACOSX_BUNDLE PolyDataConnectivityFilter_LargestRegion.cxx )

    target_link_libraries(PolyDataConnectivityFilter_LargestRegion ${VTK_LIBRARIES})

### Download and Build PolyDataConnectivityFilter_LargestRegion

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

    cd PolyDataConnectivityFilter_LargestRegion/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:

    ./PolyDataConnectivityFilter_LargestRegion

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.