# CellLocatorVisualization

VTKExamples/Cxx/PolyData/CellLocatorVisualization

### Description

The idea of this example is to navigate levels of a uniform spatial tree, vtkCellLocator, using a slider.

Note

It is not desirable to have CellsPerBucket set "too small". This is because at some point, refining a bucket will result in each cell in that bucket to also be in the bucket's children. This only wastes memory and computation. The value that is "too small" is dependent on the grid but in general a value between 10 and 100 should work well (the default value is 25).

### Code

CellLocatorVisualization.cxx

    #include <vtkPointSource.h>
    #include <vtkSphereSource.h>
    #include <vtkCellLocator.h>
    #include <vtkSmartPointer.h>
    #include <vtkPolyData.h>
    #include <vtkSliderWidget.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkActor.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkPolyData.h>
    #include <vtkSmartPointer.h>
    #include <vtkCommand.h>
    #include <vtkWidgetEvent.h>
    #include <vtkCallbackCommand.h>
    #include <vtkWidgetEventTranslator.h>
    #include <vtkInteractorStyleTrackballCamera.h>
    #include <vtkSliderWidget.h>
    #include <vtkSliderRepresentation2D.h>
    #include <vtkProperty.h>

    #include <vtkMath.h>

    class vtkSliderCallback : public vtkCommand
    {
    public:
      static vtkSliderCallback *New()
      {
        return new vtkSliderCallback;
      }
      vtkSliderCallback():CellLocator(0), Level(0), PolyData(0), Renderer(0){}

      virtual void Execute(vtkObject *caller, unsigned long, void*)
      {
        vtkSliderWidget *sliderWidget =
          reinterpret_cast<vtkSliderWidget*>(caller);
        this->Level = vtkMath::Round(static_cast<vtkSliderRepresentation *>(sliderWidget->GetRepresentation())->GetValue());
        this->CellLocator->GenerateRepresentation(this->Level, this->PolyData);
        this->Renderer->Render();
      }

      vtkCellLocator* CellLocator;
      int Level;
      vtkPolyData* PolyData;
      vtkRenderer* Renderer;
    };

    int main (int, char *[])
    {
      vtkSmartPointer<vtkSphereSource> inputSource =
        vtkSmartPointer<vtkSphereSource>::New();
      inputSource->SetPhiResolution(10);
      inputSource->SetThetaResolution(10);
      inputSource->Update();

      vtkSmartPointer<vtkPolyDataMapper> pointsMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      pointsMapper->SetInputConnection(inputSource->GetOutputPort());

      vtkSmartPointer<vtkActor> pointsActor =
        vtkSmartPointer<vtkActor>::New();
      pointsActor->SetMapper(pointsMapper);
      pointsActor->GetProperty()->SetInterpolationToFlat();

      // Create the tree
      vtkSmartPointer<vtkCellLocator> cellLocator =
        vtkSmartPointer<vtkCellLocator>::New();
      cellLocator->SetDataSet(inputSource->GetOutput());
      cellLocator->BuildLocator();

      // Initialize the representation
      vtkSmartPointer<vtkPolyData> polydata =
        vtkSmartPointer<vtkPolyData>::New();
      cellLocator->GenerateRepresentation(0, polydata);

      vtkSmartPointer<vtkPolyDataMapper> locatorTreeMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      locatorTreeMapper->SetInputData(polydata);

      vtkSmartPointer<vtkActor> locatorTreeActor =
        vtkSmartPointer<vtkActor>::New();
      locatorTreeActor->SetMapper(locatorTreeMapper);
      locatorTreeActor->GetProperty()->SetInterpolationToFlat();
      locatorTreeActor->GetProperty()->SetRepresentationToWireframe();

      // 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);

      // Add the actors to the scene
      renderer->AddActor(pointsActor);
      renderer->AddActor(locatorTreeActor);

      // Render an image (lights and cameras are created automatically)
      renderWindow->Render();

      vtkSmartPointer<vtkSliderRepresentation2D> sliderRep =
        vtkSmartPointer<vtkSliderRepresentation2D>::New();
      sliderRep->SetMinimumValue(0);
      sliderRep->SetMaximumValue(cellLocator->GetLevel());
      sliderRep->SetValue(0);
      sliderRep->SetTitleText("MaxPointsPerRegion");
      sliderRep->GetPoint1Coordinate()->SetCoordinateSystemToNormalizedDisplay();
      sliderRep->GetPoint1Coordinate()->SetValue(.2, .2);
      sliderRep->GetPoint2Coordinate()->SetCoordinateSystemToNormalizedDisplay();
      sliderRep->GetPoint2Coordinate()->SetValue(.8, .2);
      sliderRep->SetSliderLength(0.075);
      sliderRep->SetSliderWidth(0.05);
      sliderRep->SetEndCapLength(0.05);

      vtkSmartPointer<vtkSliderWidget> sliderWidget =
        vtkSmartPointer<vtkSliderWidget>::New();
      sliderWidget->SetInteractor(renderWindowInteractor);
      sliderWidget->SetRepresentation(sliderRep);
      sliderWidget->SetAnimationModeToAnimate();
      sliderWidget->EnabledOn();

      vtkSmartPointer<vtkSliderCallback> callback =
        vtkSmartPointer<vtkSliderCallback>::New();
      callback->CellLocator = cellLocator;
      callback->PolyData = polydata;
      callback->Renderer = renderer;

      sliderWidget->AddObserver(vtkCommand::InteractionEvent,callback);

      renderWindowInteractor->Initialize();
      renderWindow->Render();

      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(CellLocatorVisualization)

    find_package(VTK COMPONENTS
      vtkCommonCore
      vtkCommonDataModel
      vtkFiltersSources
      vtkInteractionStyle
      vtkInteractionWidgets
      vtkRenderingCore
      vtkRenderingFreeType
      vtkRenderingOpenGL2 QUIET)
    if (NOT VTK_FOUND)
      message("Skipping CellLocatorVisualization: ${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(CellLocatorVisualization MACOSX_BUNDLE CellLocatorVisualization.cxx )
      target_link_libraries(CellLocatorVisualization PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(CellLocatorVisualization MACOSX_BUNDLE CellLocatorVisualization.cxx )
      target_link_libraries(CellLocatorVisualization PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS CellLocatorVisualization
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build CellLocatorVisualization

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

    cd CellLocatorVisualization/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:

    ./CellLocatorVisualization

WINDOWS USERS

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