# OrientedArrow

VTKExamples/Cxx/GeometricObjects/OrientedArrow

### Description

This example illustrates how to create and display an arrow that passes through two points.

It demonstrates two different ways to apply the transform:

1. Use vtkTransformPolyDataFilter to create a new transformed polydata. This method is useful if the transformed polydata is needed later in the pipeline, e.g. vtkGlyph3DFilter.

2. Apply the transform directly to the actor using vtkProp3D's SetUserMatrix. No new data is produced.

Switch between the two methods by #defining USER_MATRIX or leaving out the #define.

Seealso

Compare this example with Oriented Cylinder . The transform is different because the cylinder height direction is along the y-axis and the arrow height is along the x axis.

### Code

OrientedArrow.cxx

    #define USER_MATRIX
    #include <vtkArrowSource.h>
    #include <vtkPolyData.h>
    #include <vtkSmartPointer.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkActor.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkMath.h>
    #include <vtkSphereSource.h>
    #include <vtkProperty.h>
    #include <vtkTransform.h>
    #include <vtkTransformPolyDataFilter.h>
    #include <time.h>

    int main(int, char *[])
    {
      //Create an arrow.
      vtkSmartPointer<vtkArrowSource> arrowSource =
        vtkSmartPointer<vtkArrowSource>::New();

      // Generate a random start and end point
      double startPoint[3], endPoint[3];
    #ifndef main
      vtkMath::RandomSeed(time(NULL));
    #else
      vtkMath::RandomSeed(8775070);
    #endif
      startPoint[0] = vtkMath::Random(-10,10);
      startPoint[1] = vtkMath::Random(-10,10);
      startPoint[2] = vtkMath::Random(-10,10);
      endPoint[0] = vtkMath::Random(-10,10);
      endPoint[1] = vtkMath::Random(-10,10);
      endPoint[2] = vtkMath::Random(-10,10);

      // Compute a basis
      double normalizedX[3];
      double normalizedY[3];
      double normalizedZ[3];

      // The X axis is a vector from start to end
      vtkMath::Subtract(endPoint, startPoint, normalizedX);
      double length = vtkMath::Norm(normalizedX);
      vtkMath::Normalize(normalizedX);

      // The Z axis is an arbitrary vector cross X
      double arbitrary[3];
      arbitrary[0] = vtkMath::Random(-10,10);
      arbitrary[1] = vtkMath::Random(-10,10);
      arbitrary[2] = vtkMath::Random(-10,10);
      vtkMath::Cross(normalizedX, arbitrary, normalizedZ);
      vtkMath::Normalize(normalizedZ);

      // The Y axis is Z cross X
      vtkMath::Cross(normalizedZ, normalizedX, normalizedY);
      vtkSmartPointer<vtkMatrix4x4> matrix =
        vtkSmartPointer<vtkMatrix4x4>::New();

      // Create the direction cosine matrix
      matrix->Identity();
      for (unsigned int i = 0; i < 3; i++)
      {
        matrix->SetElement(i, 0, normalizedX[i]);
        matrix->SetElement(i, 1, normalizedY[i]);
        matrix->SetElement(i, 2, normalizedZ[i]);
      }

      // Apply the transforms
      vtkSmartPointer<vtkTransform> transform =
        vtkSmartPointer<vtkTransform>::New();
      transform->Translate(startPoint);
      transform->Concatenate(matrix);
      transform->Scale(length, length, length);

      // Transform the polydata
      vtkSmartPointer<vtkTransformPolyDataFilter> transformPD =
        vtkSmartPointer<vtkTransformPolyDataFilter>::New();
      transformPD->SetTransform(transform);
      transformPD->SetInputConnection(arrowSource->GetOutputPort());

      //Create a mapper and actor for the arrow
      vtkSmartPointer<vtkPolyDataMapper> mapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      vtkSmartPointer<vtkActor> actor =
        vtkSmartPointer<vtkActor>::New();
    #ifdef USER_MATRIX
      mapper->SetInputConnection(arrowSource->GetOutputPort());
      actor->SetUserMatrix(transform->GetMatrix());
    #else
      mapper->SetInputConnection(transformPD->GetOutputPort());
    #endif
      actor->SetMapper(mapper);

      // Create spheres for start and end point
      vtkSmartPointer<vtkSphereSource> sphereStartSource =
        vtkSmartPointer<vtkSphereSource>::New();
        sphereStartSource->SetCenter(startPoint);
      vtkSmartPointer<vtkPolyDataMapper> sphereStartMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      sphereStartMapper->SetInputConnection(sphereStartSource->GetOutputPort());
      vtkSmartPointer<vtkActor> sphereStart =
        vtkSmartPointer<vtkActor>::New();
      sphereStart->SetMapper(sphereStartMapper);
      sphereStart->GetProperty()->SetColor(1.0, 1.0, .3);

      vtkSmartPointer<vtkSphereSource> sphereEndSource =
        vtkSmartPointer<vtkSphereSource>::New();
        sphereEndSource->SetCenter(endPoint);
      vtkSmartPointer<vtkPolyDataMapper> sphereEndMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      sphereEndMapper->SetInputConnection(sphereEndSource->GetOutputPort());
      vtkSmartPointer<vtkActor> sphereEnd =
        vtkSmartPointer<vtkActor>::New();
      sphereEnd->SetMapper(sphereEndMapper);
      sphereEnd->GetProperty()->SetColor(1.0, .3, .3);

      //Create a renderer, render window, and interactor
      vtkSmartPointer<vtkRenderer> renderer =
        vtkSmartPointer<vtkRenderer>::New();
      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->AddRenderer(renderer);
      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      renderWindowInteractor->SetRenderWindow(renderWindow);

      //Add the actor to the scene
      renderer->AddActor(actor);
      renderer->AddActor(sphereStart);
      renderer->AddActor(sphereEnd);
      renderer->SetBackground(.1, .2, .3); // Background color dark blue

      //Render and interact
      renderWindow->Render();
      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(OrientedArrow)

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

    add_executable(OrientedArrow MACOSX_BUNDLE OrientedArrow.cxx )

    target_link_libraries(OrientedArrow ${VTK_LIBRARIES})

### Download and Build OrientedArrow

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

    cd OrientedArrow/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:

    ./OrientedArrow

WINDOWS USERS

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