# PolyDataContourToImageData

VTKExamples/Cxx/PolyData/PolyDataContourToImageData

### Description

- Contributed by: Lars Friedrich

This example generates a sphere, cuts it with a plane and, therefore, generates a circlular contour vtkPolyData). Subsequently a binary image representation vtkImageData) is extracted from it. Internally vtkPolyDataToImageStencil and vtkLinearExtrusionFilter are utilized. Both the circular poly data (circle.vtp) and the resultant image (labelImage.mhd) are saved to disk.

NOTE: Similarily to example PolyDataToImageData, I am not really sure whether or not the image origin needs to be adjusted as the sphere-image-overlay shows some offset in paraview visualization (at least I think ...). Maybe someone could verify that. Thanks!

### Code

PolyDataContourToImageData.cxx

    #include <vtkVersion.h>
    #include <vtkSmartPointer.h>
    #include <vtkPolyData.h>
    #include <vtkImageData.h>
    #include <vtkSphereSource.h>
    #include <vtkMetaImageWriter.h>
    #include <vtkPolyDataToImageStencil.h>
    #include <vtkImageStencil.h>
    #include <vtkPointData.h>
    #include <vtkCutter.h>
    #include <vtkPlane.h>
    #include <vtkStripper.h>
    #include <vtkLinearExtrusionFilter.h>
    #include <vtkXMLPolyDataWriter.h>

    /**
     * This example generates a sphere, cuts it with a plane and, therefore, generates a circlular contour (vtkPolyData).
     * Subsequently a binary image representation (vtkImageData) is extracted from it. Internally vtkPolyDataToImageStencil and
     * vtkLinearExtrusionFilter are utilized. Both the circular poly data (circle.vtp) and the resultant image (labelImage.mhd)
     * are saved to disk.
     */
    int main(int, char *[])
    {
      // 3D source sphere
      vtkSmartPointer<vtkSphereSource> sphereSource =
        vtkSmartPointer<vtkSphereSource>::New();
      sphereSource->SetPhiResolution(30);
      sphereSource->SetThetaResolution(30);
      sphereSource->SetCenter(40, 40, 0);
      sphereSource->SetRadius(20);

      // generate circle by cutting the sphere with an implicit plane
      // (through its center, axis-aligned)
      vtkSmartPointer<vtkCutter> circleCutter =
        vtkSmartPointer<vtkCutter>::New();
      circleCutter->SetInputConnection(sphereSource->GetOutputPort());
      vtkSmartPointer<vtkPlane> cutPlane =
        vtkSmartPointer<vtkPlane>::New();
      cutPlane->SetOrigin(sphereSource->GetCenter());
      cutPlane->SetNormal(0, 0, 1);
      circleCutter->SetCutFunction(cutPlane);

      vtkSmartPointer<vtkStripper> stripper =
        vtkSmartPointer<vtkStripper>::New();
      stripper->SetInputConnection(circleCutter->GetOutputPort()); // valid circle
      stripper->Update();

      // that's our circle
      vtkSmartPointer<vtkPolyData> circle = stripper->GetOutput();

      // write circle out
      vtkSmartPointer<vtkXMLPolyDataWriter> polyDataWriter =
          vtkSmartPointer<vtkXMLPolyDataWriter>::New();
    #if VTK_MAJOR_VERSION <= 5
      polyDataWriter->SetInput(circle);
    #else
      polyDataWriter->SetInputData(circle);
    #endif
      polyDataWriter->SetFileName("circle.vtp");
      polyDataWriter->SetCompressorTypeToNone();
      polyDataWriter->SetDataModeToAscii();
      polyDataWriter->Write();

      // prepare the binary image's voxel grid
      vtkSmartPointer<vtkImageData> whiteImage =
          vtkSmartPointer<vtkImageData>::New();
      double bounds[6];
      circle->GetBounds(bounds);
      double spacing[3]; // desired volume spacing
      spacing[0] = 0.5;
      spacing[1] = 0.5;
      spacing[2] = 0.5;
      whiteImage->SetSpacing(spacing);

      // compute dimensions
      int dim[3];
      for (int i = 0; i < 3; i++)
      {
        dim[i] = static_cast<int>(ceil((bounds[i * 2 + 1] - bounds[i * 2]) /
            spacing[i])) + 1;
        if (dim[i] < 1)
          dim[i] = 1;
      }
      whiteImage->SetDimensions(dim);
      whiteImage->SetExtent(0, dim[0] - 1, 0, dim[1] - 1, 0, dim[2] - 1);
      double origin[3];

      // NOTE: I am not sure whether or not we had to add some offset!
      origin[0] = bounds[0];// + spacing[0] / 2;
      origin[1] = bounds[2];// + spacing[1] / 2;
      origin[2] = bounds[4];// + spacing[2] / 2;
      whiteImage->SetOrigin(origin);

    #if VTK_MAJOR_VERSION <= 5
      whiteImage->SetScalarTypeToUnsignedChar();
      whiteImage->AllocateScalars();
    #else
      whiteImage->AllocateScalars(VTK_UNSIGNED_CHAR,1);
    #endif

      // fill the image with foreground voxels:
      unsigned char inval = 255;
      unsigned char outval = 0;
      vtkIdType count = whiteImage->GetNumberOfPoints();
      for (vtkIdType i = 0; i < count; ++i)
      {
        whiteImage->GetPointData()->GetScalars()->SetTuple1(i, inval);
      }

      // sweep polygonal data (this is the important thing with contours!)
      vtkSmartPointer<vtkLinearExtrusionFilter> extruder =
          vtkSmartPointer<vtkLinearExtrusionFilter>::New();
    #if VTK_MAJOR_VERSION <= 5
      extruder->SetInput(circle);
    #else
      extruder->SetInputData(circle);
    #endif
      extruder->SetScaleFactor(1.);
      extruder->SetExtrusionTypeToNormalExtrusion();
      extruder->SetVector(0, 0, 1);
      extruder->Update();

      // polygonal data --> image stencil:
      vtkSmartPointer<vtkPolyDataToImageStencil> pol2stenc =
        vtkSmartPointer<vtkPolyDataToImageStencil>::New();
      pol2stenc->SetTolerance(0); // important if extruder->SetVector(0, 0, 1) !!!
      pol2stenc->SetInputConnection(extruder->GetOutputPort());
      pol2stenc->SetOutputOrigin(origin);
      pol2stenc->SetOutputSpacing(spacing);
      pol2stenc->SetOutputWholeExtent(whiteImage->GetExtent());
      pol2stenc->Update();

      // cut the corresponding white image and set the background:
      vtkSmartPointer<vtkImageStencil> imgstenc =
        vtkSmartPointer<vtkImageStencil>::New();
    #if VTK_MAJOR_VERSION <= 5
      imgstenc->SetInput(whiteImage);
      imgstenc->SetStencil(pol2stenc->GetOutput());
    #else
      imgstenc->SetInputData(whiteImage);
      imgstenc->SetStencilConnection(pol2stenc->GetOutputPort());
    #endif
      imgstenc->ReverseStencilOff();
      imgstenc->SetBackgroundValue(outval);
      imgstenc->Update();
      imgstenc->GetOutput()->Print(std::cout);

      vtkSmartPointer<vtkMetaImageWriter> imageWriter =
        vtkSmartPointer<vtkMetaImageWriter>::New();
      imageWriter->SetFileName("labelImage.mhd");
      imageWriter->SetInputConnection(imgstenc->GetOutputPort());
      imageWriter->Write();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(PolyDataContourToImageData)

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

    add_executable(PolyDataContourToImageData MACOSX_BUNDLE PolyDataContourToImageData.cxx )

    target_link_libraries(PolyDataContourToImageData ${VTK_LIBRARIES})

### Download and Build PolyDataContourToImageData

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

    cd PolyDataContourToImageData/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:

    ./PolyDataContourToImageData

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.