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# GreedyTerrainDecimation

VTKEx/Cxx/PolyData/GreedyTerrainDecimation

Other languages

See (CSharp)

Question

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### Code

GreedyTerrainDecimation.cxx

    #include <vtkPolyData.h>
    #include <vtkProperty.h>
    #include <vtkMath.h>
    #include <vtkSmartPointer.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkActor.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkImageData.h>
    #include <vtkGreedyTerrainDecimation.h>

    int main(int, char *[])
    {
      // Create an image
      vtkSmartPointer<vtkImageData> image =
        vtkSmartPointer<vtkImageData>::New();
      image->SetDimensions(3,3,1);
      image->AllocateScalars(VTK_UNSIGNED_CHAR,1);

      int dims[3];
      image->GetDimensions(dims);
      for(int i = 0; i < dims[0]; i++)
      {
        for(int j = 0; j < dims[1]; j++)
        {
          unsigned char* pixel = static_cast<unsigned char*>(image->GetScalarPointer(i,j,0));
          //pixel[0] = vtkMath::Round(vtkMath::Random(0, 255));
          pixel[0] = vtkMath::Round(vtkMath::Random(0, 1));
        }
      }

      vtkSmartPointer<vtkGreedyTerrainDecimation> decimation =
        vtkSmartPointer<vtkGreedyTerrainDecimation>::New();
      decimation->SetInputData(image);
      decimation->Update();

      // Visualize
      vtkSmartPointer<vtkPolyDataMapper> mapper =
          vtkSmartPointer<vtkPolyDataMapper>::New();
      mapper->SetInputConnection(decimation->GetOutputPort());

      vtkSmartPointer<vtkActor> actor =
          vtkSmartPointer<vtkActor>::New();
      actor->SetMapper(mapper);
      actor->GetProperty()->SetInterpolationToFlat();
      actor->GetProperty()->EdgeVisibilityOn();
      actor->GetProperty()->SetEdgeColor(1,0,0);

      vtkSmartPointer<vtkRenderer> renderer =
          vtkSmartPointer<vtkRenderer>::New();
      vtkSmartPointer<vtkRenderWindow> renderWindow =
          vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->AddRenderer(renderer);
      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
          vtkSmartPointer<vtkRenderWindowInteractor>::New();
      renderWindowInteractor->SetRenderWindow(renderWindow);

      renderer->AddActor(actor);
      renderer->SetBackground(1,1,1); // Background color white

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

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(GreedyTerrainDecimation)

    find_package(VTK COMPONENTS
      vtkCommonCore
      vtkCommonDataModel
      vtkFiltersHybrid
      vtkInteractionStyle
      vtkRenderingContextOpenGL2
      vtkRenderingCore
      vtkRenderingFreeType
      vtkRenderingGL2PSOpenGL2
      vtkRenderingOpenGL2 QUIET)
    if (NOT VTK_FOUND)
      message("Skipping GreedyTerrainDecimation: ${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(GreedyTerrainDecimation MACOSX_BUNDLE GreedyTerrainDecimation.cxx )
      target_link_libraries(GreedyTerrainDecimation PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(GreedyTerrainDecimation MACOSX_BUNDLE GreedyTerrainDecimation.cxx )
      target_link_libraries(GreedyTerrainDecimation PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS GreedyTerrainDecimation
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build GreedyTerrainDecimation

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

    cd GreedyTerrainDecimation/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:

    ./GreedyTerrainDecimation

WINDOWS USERS

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