# VectorField

VTKExamples/Cxx/Visualization/VectorField

### Code

VectorField.cxx

    #include <vtkVersion.h>
    #include <vtkArrowSource.h>
    #include <vtkCellArray.h>
    #include <vtkGlyph2D.h>
    #include <vtkPointData.h>
    #include <vtkImageData.h>
    #include <vtkImageSliceMapper.h>
    #include <vtkImageSlice.h>
    #include <vtkInteractorStyleImage.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkPolyData.h>
    #include <vtkPoints.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkSmartPointer.h>
    #include <vtkXMLPolyDataWriter.h>

    int main(int, char *[])
    {
      // Create an image
      vtkSmartPointer<vtkImageData> image = vtkSmartPointer<vtkImageData>::New();

      // Specify the size of the image data
      image->SetDimensions(50,50,1);

    #if VTK_MAJOR_VERSION <= 5
      image->SetNumberOfScalarComponents(2);
      image->SetScalarTypeToFloat();
      image->AllocateScalars();
    #else
      image->AllocateScalars(VTK_FLOAT,2);
    #endif
      int* dims = image->GetDimensions();

      // Zero the image
      for (int y = 0; y < dims[1]; y++)
      {
        for (int x = 0; x < dims[0]; x++)
        {
          float* pixel = static_cast<float*>(image->GetScalarPointer(x,y,0));
          pixel[0] = 0.0;
          pixel[1] = 0.0;
        }
      }

      {
      float* pixel = static_cast<float*>(image->GetScalarPointer(20,20,0));
      pixel[0] = -10.0;
      pixel[1] = 5.0;
      }

      {
      float* pixel = static_cast<float*>(image->GetScalarPointer(30,30,0));
      pixel[0] = 10.0;
      pixel[1] = 10.0;
      }

      // A better way to do this is (should be tested for compilablilty and correctness):
      // image->GetPointData()->SetActiveVectors(image->GetPointData()->GetScalars()->GetName().c_str());
      image->GetPointData()->SetActiveVectors("ImageScalars");

      // Setup the arrows
      vtkSmartPointer<vtkArrowSource> arrowSource = vtkSmartPointer<vtkArrowSource>::New();
      arrowSource->Update();

      vtkSmartPointer<vtkGlyph2D> glyphFilter = vtkSmartPointer<vtkGlyph2D>::New();
      glyphFilter->SetSourceConnection(arrowSource->GetOutputPort());
      glyphFilter->OrientOn();
      glyphFilter->SetVectorModeToUseVector();
    #if VTK_MAJOR_VERSION <= 5
      glyphFilter->SetInputConnection(image->GetProducerPort());
    #else
      glyphFilter->SetInputData(image);
    #endif
      glyphFilter->Update();

      // Create actors
      vtkSmartPointer<vtkImageSliceMapper> imageMapper = vtkSmartPointer<vtkImageSliceMapper>::New();
    #if VTK_MAJOR_VERSION <= 5
      imageMapper->SetInputConnection(image->GetProducerPort());
    #else
      imageMapper->SetInputData(image);
    #endif

      vtkSmartPointer<vtkImageSlice> imageSlice = vtkSmartPointer<vtkImageSlice>::New();
      imageSlice->SetMapper(imageMapper);

      vtkSmartPointer<vtkPolyDataMapper> vectorMapper = vtkSmartPointer<vtkPolyDataMapper>::New();
      vectorMapper->SetInputConnection(glyphFilter->GetOutputPort());
      vtkSmartPointer<vtkActor> vectorActor = vtkSmartPointer<vtkActor>::New();
      vectorActor->SetMapper(vectorMapper);

      // Setup renderer
      vtkSmartPointer<vtkRenderer> renderer = vtkSmartPointer<vtkRenderer>::New();
      renderer->AddViewProp(imageSlice);
      renderer->AddViewProp(vectorActor);
      renderer->ResetCamera();

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

      // Setup render window interactor
      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor = vtkSmartPointer<vtkRenderWindowInteractor>::New();
      vtkSmartPointer<vtkInteractorStyleImage> style = vtkSmartPointer<vtkInteractorStyleImage>::New();
      //renderWindowInteractor->SetInteractorStyle(style);

      // Render and start interaction
      renderWindowInteractor->SetRenderWindow(renderWindow);
      renderWindowInteractor->Initialize();

      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(VectorField)

    find_package(VTK REQUIRED)
    include(${VTK_USE_FILE})

    add_executable(VectorField MACOSX_BUNDLE VectorField.cxx)

    target_link_libraries(VectorField ${VTK_LIBRARIES})

### Download and Build VectorField

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

    cd VectorField/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:

    ./VectorField

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