# LabelContours

VTKExamples/Cxx/Visualization/LabelContours

### Description

This example labels isolines created by vtkContourFilter. After the isolines are generated, the resulting disconnected lines segments are gathered into polylines by vtkStripper. Then an appropriate position along each line is chosen to place the label for the contour. Two strategies for label placement are illustrated: a point at the midpoint of the line or a random point. vtkLabeledDataMapper places the labels for the contour lines.

The program can be run with an input XML polydata file (.vtp) or without arguments. If a file is specified then one, two or a range of contours can be specified. If run without a file name, the example generates a random scalar field on a plane.

Note

The labels are represented as vtkActor2D's. If they are generated for a 3D surface, the labels that should be hidden will still be displayed.

### Code

LabelContours.cxx

    #include <vtkSmartPointer.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>

    #include <vtkXMLPolyDataReader.h>
    #include <vtkContourFilter.h>
    #include <vtkStripper.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkLabeledDataMapper.h>
    #include <vtkPlaneSource.h>
    #include <vtkLookupTable.h>
    #include <vtkProperty.h>
    #include <vtkActor.h>
    #include <vtkActor2D.h>

    #include <vtkCellArray.h>
    #include <vtkPoints.h>
    #include <vtkPointData.h>
    #include <vtkDataArray.h>
    #include <vtkDoubleArray.h>

    #include <vtkMath.h>

    int main (int argc, char *argv[])
    {
      int pointThreshold = 10;

      vtkSmartPointer<vtkPolyData> polyData =
        vtkSmartPointer<vtkPolyData>::New();
      vtkSmartPointer<vtkContourFilter> contours =
        vtkSmartPointer<vtkContourFilter>::New();

      // If a file is present, read it, otherwise generate some random
      // scalars on a plane
      if (argc > 1)
      {
        vtkSmartPointer<vtkXMLPolyDataReader> reader =
          vtkSmartPointer<vtkXMLPolyDataReader>::New();
        reader->SetFileName(argv[1]);
        reader->Update();

        double range[2];
        reader->GetOutput()->GetScalarRange(range);
        polyData = reader->GetOutput();

        std::cout << "range: " << range[0] << ", " << range[1] << std::endl;
        contours->SetValue(0, (range[1] + range[0]) / 2.0);

        contours->SetInputConnection(reader->GetOutputPort());
        if (argc == 3)
        {
          contours->SetValue(0, atof(argv[2]));
        }
        else if (argc == 4)
        {
          contours->SetValue(0, atof(argv[2]));
          contours->SetValue(1, atof(argv[3]));
        }
        else if (argc == 5)
        {
          contours->GenerateValues(atoi(argv[2]),
                                   atof(argv[3]),
                                   atof(argv[4]));
        }
      }
      else
      {
        vtkSmartPointer<vtkPlaneSource> plane =
          vtkSmartPointer<vtkPlaneSource>::New();
        plane->SetXResolution(10);
        plane->SetYResolution(10);
        plane->Update();

        vtkSmartPointer<vtkDoubleArray> randomScalars =
          vtkSmartPointer<vtkDoubleArray>::New();
        randomScalars->SetNumberOfComponents(1);
        randomScalars->SetName("Isovalues");
        for (int i = 0; i < plane->GetOutput()->GetNumberOfPoints(); i++)
        {
          randomScalars->InsertNextTuple1(vtkMath::Random(-100.0, 100.0));
        }
        plane->GetOutput()->GetPointData()->SetScalars(randomScalars);
        polyData = plane->GetOutput();
        contours->SetInputConnection(plane->GetOutputPort());
        contours->GenerateValues(5, -100, 100);
        pointThreshold = 0;
      }

      // Connect the segments of the conours into polylines
      vtkSmartPointer<vtkStripper> contourStripper =
        vtkSmartPointer<vtkStripper>::New();
      contourStripper->SetInputConnection(contours->GetOutputPort());
      contourStripper->Update();

      int numberOfContourLines = contourStripper->GetOutput()->GetNumberOfLines();

      std::cout << "There are "
                << numberOfContourLines << " contours lines."
                << std::endl;

      vtkPoints *points     =
        contourStripper->GetOutput()->GetPoints();
      vtkCellArray *cells   =
        contourStripper->GetOutput()->GetLines();
      vtkDataArray *scalars =
        contourStripper->GetOutput()->GetPointData()->GetScalars();

      // Create a polydata that contains point locations for the contour
      // line labels
      vtkSmartPointer<vtkPolyData> labelPolyData =
        vtkSmartPointer<vtkPolyData>::New();
      vtkSmartPointer<vtkPoints> labelPoints =
        vtkSmartPointer<vtkPoints>::New();
      vtkSmartPointer<vtkDoubleArray> labelScalars =
        vtkSmartPointer<vtkDoubleArray>::New();
      labelScalars->SetNumberOfComponents(1);
      labelScalars->SetName("Isovalues");

      vtkIdType *indices;
      vtkIdType numberOfPoints;
      unsigned int lineCount = 0;
      for (cells->InitTraversal();
           cells->GetNextCell(numberOfPoints, indices);
           lineCount++)
      {
        if (numberOfPoints < pointThreshold)
        {
          continue;
        }
        std::cout << "Line " << lineCount << ": " << std::endl;

        // Compute the point id to hold the label
        // Mid point or a random point
        vtkIdType midPointId = indices[numberOfPoints / 2];
        midPointId =
          indices[static_cast<vtkIdType>(vtkMath::Random(0, numberOfPoints))];

        double midPoint[3];
        points->GetPoint(midPointId, midPoint);
        std::cout << "\tmidPoint is " << midPointId << " with coordinate "
                  << "("
                  << midPoint[0] << ", "
                  << midPoint[1] << ", "
                  << midPoint[2] << ")"
                  << " and value " << scalars->GetTuple1(midPointId)
                  << std::endl;
        labelPoints->InsertNextPoint(midPoint);
        labelScalars->InsertNextTuple1(scalars->GetTuple1(midPointId));
      }
      labelPolyData->SetPoints(labelPoints);
      labelPolyData->GetPointData()->SetScalars(labelScalars);

      vtkSmartPointer<vtkPolyDataMapper> contourMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      contourMapper->SetInputConnection(contourStripper->GetOutputPort());
      contourMapper->ScalarVisibilityOff();

      vtkSmartPointer<vtkActor> isolines =
        vtkSmartPointer<vtkActor>::New();
      isolines->SetMapper(contourMapper);

      vtkSmartPointer<vtkLookupTable> surfaceLUT =
        vtkSmartPointer<vtkLookupTable>::New();
      surfaceLUT->SetRange(
        polyData->GetPointData()->GetScalars()->GetRange());
      surfaceLUT->Build();

      vtkSmartPointer<vtkPolyDataMapper> surfaceMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      surfaceMapper->SetInputData(polyData);
      surfaceMapper->ScalarVisibilityOn();
      surfaceMapper->SetScalarRange(
        polyData->GetPointData()->GetScalars()->GetRange());
      surfaceMapper->SetLookupTable(surfaceLUT);

      vtkSmartPointer<vtkActor> surface =
        vtkSmartPointer<vtkActor>::New();
      surface->SetMapper(surfaceMapper);

      // The labeled data mapper will place labels at the points
      vtkSmartPointer<vtkLabeledDataMapper> labelMapper =
        vtkSmartPointer<vtkLabeledDataMapper>::New();
      labelMapper->SetFieldDataName("Isovalues");
      labelMapper->SetInputData(labelPolyData);
      labelMapper->SetLabelModeToLabelScalars();
      labelMapper->SetLabelFormat("%6.2f");

      vtkSmartPointer<vtkActor2D> isolabels =
        vtkSmartPointer<vtkActor2D>::New();
      isolabels->SetMapper(labelMapper);

      // Create a renderer and render window
      vtkSmartPointer<vtkRenderer> renderer =
          vtkSmartPointer<vtkRenderer>::New();

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

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

      // Add the actors to the scene
      renderer->AddActor(isolines);
      renderer->AddActor(isolabels);
    //  renderer->AddActor(surface);

      // Render the scene (lights and cameras are created automatically)
      renderWindow->Render();
      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(LabelContours)

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

### Download and Build LabelContours

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

    cd LabelContours/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:

    ./LabelContours

WINDOWS USERS

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