# OrientedCylinder

VTKExamples/Cxx/GeometricObjects/OrientedCylinder

### Description

This example illustrates how to create and display a cylinder 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.

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

### Code

OrientedCylinder.cxx

    #define USER_MATRIX
    #include <vtkCylinderSource.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 cylinder.
      // Cylinder height vector is (0,1,0).
      // Cylinder center is in the middle of the cylinder
      vtkSmartPointer<vtkCylinderSource> cylinderSource =
        vtkSmartPointer<vtkCylinderSource>::New();
      cylinderSource->SetResolution(15);

      // 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);   // translate to starting point
      transform->Concatenate(matrix);     // apply direction cosines
      transform->RotateZ(-90.0);          // align cylinder to x axis
      transform->Scale(1.0, length, 1.0); // scale along the height vector
      transform->Translate(0, .5, 0);     // translate to start of cylinder

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

      //Create a mapper and actor for the cylinder
      vtkSmartPointer<vtkPolyDataMapper> mapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      vtkSmartPointer<vtkActor> actor =
        vtkSmartPointer<vtkActor>::New();
    #ifdef USER_MATRIX
      mapper->SetInputConnection(cylinderSource->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(OrientedCylinder)

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

    add_executable(OrientedCylinder MACOSX_BUNDLE OrientedCylinder.cxx)

    target_link_libraries(OrientedCylinder ${VTK_LIBRARIES})

### Download and Build OrientedCylinder

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

    cd OrientedCylinder/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:

    ./OrientedCylinder

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.