# ClipFrustum

VTKExamples/Cxx/Meshes/ClipFrustum

### Description

The example uses vtkClipPolyData to clip a model with a vtkCamera's view frustum. The frustum is displayed using vtkFrustumSource.

The example proceeds as follow:

1. Read a vtkPolyData. The example can read any of the supported polydata readers.
2. Generates a view of the model.
3. Recovers the view frustum of the current vtkCamera.
4. Creates an implicit function using vtkPlanes::SetFrustumPlanes.
5. Passes the vtkPlanes to vtkFrustumSource.
6. Passes the vtkPlanes to vtkClipPolyData as the ClipFunction.
7. Tells vtkClipPolyData to generate vtkPolyData for inside and outside.
8. Presents the frustum, and clipped models. The inside model is red and the outside model is gold.

Bug

The first attempt to write the example used vtkClipConvexPolyData, but that filter has bugs and only works with one plane.

### Code

ClipFrustum.cxx

    #include <vtkSmartPointer.h>

    #include <vtkFrustumSource.h>
    #include <vtkClipPolyData.h>

    #include <vtkPlanes.h>
    #include <vtkNamedColors.h>
    #include <vtkPolyDataNormals.h>

    #include <vtkBYUReader.h>
    #include <vtkOBJReader.h>
    #include <vtkPLYReader.h>
    #include <vtkPolyDataReader.h>
    #include <vtkSTLReader.h>
    #include <vtkXMLPolyDataReader.h>
    #include <vtkSphereSource.h>

    #include <vtksys/SystemTools.hxx>

    #include <vtkProperty.h>
    #include <vtkCamera.h>
    #include <vtkMapper.h>
    #include <vtkActor.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkPolyDataMapper.h>

    #include <vtkCamera.h>
    namespace
    {
    vtkSmartPointer<vtkPolyData> ReadPolyData(const char *fileName);
    void PositionCamera(vtkSmartPointer<vtkRenderer> &renderer,
                        double *viewUp,
                        double *position);
    }

    int main (int argc, char *argv[])
    {
      vtkSmartPointer<vtkPolyData> polyData = ReadPolyData(argc > 1 ? argv[1] : "");;

      vtkSmartPointer<vtkNamedColors> colors =
        vtkSmartPointer<vtkNamedColors>::New();

      // a renderer and render window
      vtkSmartPointer<vtkRenderer> renderer =
        vtkSmartPointer<vtkRenderer>::New();
      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->AddRenderer(renderer);

      // an interactor
      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      renderWindowInteractor->SetRenderWindow(renderWindow);

      vtkSmartPointer<vtkPolyDataMapper> mapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      mapper->SetInputData(polyData);
      mapper->ScalarVisibilityOff();

      vtkSmartPointer<vtkActor> actor =
        vtkSmartPointer<vtkActor>::New();
      actor->SetMapper(mapper);
      actor->GetProperty()->SetDiffuseColor(colors->GetColor3d("Crimson").GetData());
      actor->GetProperty()->SetSpecular(.6);
      actor->GetProperty()->SetSpecularPower(30);
      renderer->AddActor(actor);

      vtkSmartPointer<vtkPolyDataMapper> outMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      outMapper->SetInputData(polyData);
      outMapper->ScalarVisibilityOff();

      vtkSmartPointer<vtkActor> outActor =
        vtkSmartPointer<vtkActor>::New();
      outActor->SetMapper(outMapper);
      outActor->GetProperty()->SetDiffuseColor(colors->GetColor3d("Gold").GetData());
      outActor->GetProperty()->SetSpecular(.6);
      outActor->GetProperty()->SetSpecularPower(30);

      // Position the camera so that we can see the frustum
      double viewUp[3] = {0.0,1.0,0.0};
      double position[3] = {1.0,0.0,0.0};
      PositionCamera(renderer, viewUp, position);
      renderer->GetActiveCamera()->Elevation(30);
      renderer->GetActiveCamera()->SetViewAngle(10.0);

      double planesArray[24];
      renderer->GetActiveCamera()->GetFrustumPlanes(1.0, planesArray);

      vtkSmartPointer<vtkPlanes> planes =
        vtkSmartPointer<vtkPlanes>::New();
      planes->SetFrustumPlanes(planesArray);

      vtkSmartPointer<vtkFrustumSource> frustumSource =
        vtkSmartPointer<vtkFrustumSource>::New();
      frustumSource->ShowLinesOff();
      frustumSource->SetPlanes(planes);
      frustumSource->Update();

      vtkSmartPointer<vtkPolyDataMapper> frustumMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      frustumMapper->SetInputConnection(frustumSource->GetOutputPort());

      vtkSmartPointer<vtkActor> frustumActor =
        vtkSmartPointer<vtkActor>::New();
      frustumActor->SetMapper(frustumMapper);
      frustumActor->GetProperty()->EdgeVisibilityOn();
      frustumActor->GetProperty()->SetOpacity(.5);
      frustumActor->GetProperty()->SetColor(colors->GetColor3d("Banana").GetData());

      vtkSmartPointer<vtkClipPolyData> clip =
        vtkSmartPointer<vtkClipPolyData>::New();
      clip->SetInputData(polyData);
      clip->SetClipFunction(planes);
      clip->InsideOutOn();
      clip->GenerateClippedOutputOn();
      clip->Update();

      mapper->SetInputConnection(clip->GetOutputPort());
      outMapper->SetInputData(clip->GetClippedOutput());

      renderer->SetBackground(colors->GetColor3d("Silver").GetData());
      renderer->AddActor(frustumActor);
      renderer->AddActor(outActor);

      renderer->ResetCamera();
      renderer->GetActiveCamera()->Azimuth(30);
      renderer->GetActiveCamera()->Elevation(30);
      renderer->GetActiveCamera()->Dolly(1.5);
      renderer->ResetCameraClippingRange();
      renderWindow->SetSize(640, 480);
      renderWindow->Render();

      // begin mouse interaction
      renderWindowInteractor->Start();
      return EXIT_SUCCESS;
    }

    // Snippets
    namespace
    {
    vtkSmartPointer<vtkPolyData> ReadPolyData(const char *fileName)
    {
      vtkSmartPointer<vtkPolyData> polyData;
      std::string extension = vtksys::SystemTools::GetFilenameExtension(std::string(fileName));
      if (extension == ".ply")
      {
        vtkSmartPointer<vtkPLYReader> reader =
          vtkSmartPointer<vtkPLYReader>::New();
        reader->SetFileName (fileName);
        reader->Update();
        polyData = reader->GetOutput();
      }
      else if (extension == ".vtp")
      {
        vtkSmartPointer<vtkXMLPolyDataReader> reader =
          vtkSmartPointer<vtkXMLPolyDataReader>::New();
        reader->SetFileName (fileName);
        reader->Update();
        polyData = reader->GetOutput();
      }
      else if (extension == ".obj")
      {
        vtkSmartPointer<vtkOBJReader> reader =
          vtkSmartPointer<vtkOBJReader>::New();
        reader->SetFileName (fileName);
        reader->Update();
        polyData = reader->GetOutput();
      }
      else if (extension == ".stl")
      {
        vtkSmartPointer<vtkSTLReader> reader =
          vtkSmartPointer<vtkSTLReader>::New();
        reader->SetFileName (fileName);
        reader->Update();
        polyData = reader->GetOutput();
      }
      else if (extension == ".vtk")
      {
        vtkSmartPointer<vtkPolyDataReader> reader =
          vtkSmartPointer<vtkPolyDataReader>::New();
        reader->SetFileName (fileName);
        reader->Update();
        polyData = reader->GetOutput();
      }
      else if (extension == ".g")
      {
        vtkSmartPointer<vtkBYUReader> reader =
          vtkSmartPointer<vtkBYUReader>::New();
        reader->SetGeometryFileName (fileName);
        reader->Update();
        polyData = reader->GetOutput();
      }
      else
      {
        vtkSmartPointer<vtkSphereSource> source =
          vtkSmartPointer<vtkSphereSource>::New();
        source->Update();
        polyData = source->GetOutput();
      }
      return polyData;
    }

    void PositionCamera(vtkSmartPointer<vtkRenderer> &renderer,
                        double *viewUp,
                        double *position)
    {
      renderer->GetActiveCamera()->SetFocalPoint(0.0, 0.0, 0.0);
      renderer->GetActiveCamera()->SetViewUp(viewUp);
      renderer->GetActiveCamera()->SetPosition(position);
      renderer->ResetCamera();
      return;
    }
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(ClipFrustum)

    find_package(VTK COMPONENTS
      vtkCommonColor
      vtkCommonCore
      vtkCommonDataModel
      vtkFiltersCore
      vtkFiltersSources
      vtkIOGeometry
      vtkIOLegacy
      vtkIOPLY
      vtkIOXML
      vtkInteractionStyle
      vtkRenderingCore
      vtkRenderingFreeType
      vtkRenderingOpenGL2 QUIET)
    if (NOT VTK_FOUND)
      message("Skipping ClipFrustum: ${VTK_NOT_FOUND_MESSAGE}")
      return ()
    endif()
    message (STATUS "VTK_VERSION: ${VTK_VERSION}")
    if (VTK_VERSION VERSION_LESS "8.90.0")
      # old system
      include(${VTK_USE_FILE})
      add_executable(ClipFrustum MACOSX_BUNDLE ClipFrustum.cxx )
      target_link_libraries(ClipFrustum PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(ClipFrustum MACOSX_BUNDLE ClipFrustum.cxx )
      target_link_libraries(ClipFrustum PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS ClipFrustum
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build ClipFrustum

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

    cd ClipFrustum/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:

    ./ClipFrustum

WINDOWS USERS

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