# ElevationFilter

VTKExamples/Cxx/Meshes/ElevationFilter

Other Languages

See (CSharp)

### Code

ElevationFilter.cxx

    #include <vtkPoints.h>
    #include <vtkPolyData.h>
    #include <vtkPointData.h>
    #include <vtkSmartPointer.h>
    #include <vtkDelaunay2D.h>
    #include <vtkXMLPolyDataWriter.h>
    #include <vtkLookupTable.h>
    #include <vtkFloatArray.h>
    #include <vtkElevationFilter.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkActor.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindowInteractor.h>

    // For compatibility with new VTK generic data arrays
    #ifdef vtkGenericDataArray_h
    #define InsertNextTupleValue InsertNextTypedTuple
    #endif

    int main(int, char *[])
    {
      // Created a grid of points (heigh/terrian map)
      vtkSmartPointer<vtkPoints> points =
        vtkSmartPointer<vtkPoints>::New();

      unsigned int gridSize = 10;
      for(unsigned int x = 0; x < gridSize; x++)
      {
        for(unsigned int y = 0; y < gridSize; y++)
        {
          points->InsertNextPoint(x, y, (x+y)/(y+1));
        }
      }

      double bounds[6];
      points->GetBounds(bounds);

      // Add the grid points to a polydata object
      vtkSmartPointer<vtkPolyData> inputPolyData =
        vtkSmartPointer<vtkPolyData>::New();
      inputPolyData->SetPoints(points);

      // Triangulate the grid points
      vtkSmartPointer<vtkDelaunay2D> delaunay =
        vtkSmartPointer<vtkDelaunay2D>::New();
      delaunay->SetInputData(inputPolyData);
      delaunay->Update();

      vtkSmartPointer<vtkElevationFilter> elevationFilter =
        vtkSmartPointer<vtkElevationFilter>::New();
      elevationFilter->SetInputConnection(delaunay->GetOutputPort());
      elevationFilter->SetLowPoint(0.0, 0.0, bounds[4]);
      elevationFilter->SetHighPoint(0.0, 0.0, bounds[5]);
      elevationFilter->Update();

      vtkSmartPointer<vtkPolyData> output =
        vtkSmartPointer<vtkPolyData>::New();
      output->ShallowCopy(vtkPolyData::SafeDownCast(elevationFilter->GetOutput()));

      vtkFloatArray* elevation = vtkFloatArray::SafeDownCast(output->GetPointData()->GetArray("Elevation"));

      // Create the color map
      vtkSmartPointer<vtkLookupTable> colorLookupTable =
        vtkSmartPointer<vtkLookupTable>::New();
      colorLookupTable->SetTableRange(bounds[4], bounds[5]);
      colorLookupTable->Build();

      // Generate the colors for each point based on the color map
      vtkSmartPointer<vtkUnsignedCharArray> colors =
        vtkSmartPointer<vtkUnsignedCharArray>::New();
      colors->SetNumberOfComponents(3);
      colors->SetName("Colors");

      for(vtkIdType i = 0; i < output->GetNumberOfPoints(); i++)
      {
        double val = elevation->GetValue(i);
        std::cout << "val: " << val << std::endl;

        double dcolor[3];
        colorLookupTable->GetColor(val, dcolor);
        std::cout << "dcolor: " << dcolor[0] << " " << dcolor[1] << " " << dcolor[2] << std::endl;
        unsigned char color[3];
        for(unsigned int j = 0; j < 3; j++)
        {
          color[j] = 255 * dcolor[j]/1.0;
        }
        std::cout << "color: " << (int)color[0] << " " << (int)color[1] << " " << (int)color[2] << std::endl;

        colors->InsertNextTupleValue(color);
      }

      output->GetPointData()->AddArray(colors);

      // Visualize
      vtkSmartPointer<vtkPolyDataMapper> mapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      mapper->SetInputData(output);

      vtkSmartPointer<vtkActor> actor =
        vtkSmartPointer<vtkActor>::New();
      actor->SetMapper(mapper);

      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(.3, .6, .3); // Background color green

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

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(ElevationFilter)

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

### Download and Build ElevationFilter

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

    cd ElevationFilter/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:

    ./ElevationFilter

WINDOWS USERS

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