# ConstrainedDelaunay2D

VTKExamples/Cxx/Filtering/ConstrainedDelaunay2D

### Description

Perform a 2D Delaunay triangulation respecting a specified boundary. This examples constructs a 10x10 grid of points. It then defines a polygon that uses the points in the grid. We want to triangulate all of the points except the region inside the boundary of the polygon. We expect a rectangular hole of size 4x3 in the resulting triangulated plane.

### Code

ConstrainedDelaunay2D.cxx

    #include <vtkSmartPointer.h>
    #include <vtkDelaunay2D.h>

    #include <vtkCellArray.h>
    #include <vtkProperty.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkActor.h>
    #include <vtkPoints.h>
    #include <vtkPolyData.h>
    #include <vtkPolygon.h>
    #include <vtkMath.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkNamedColors.h>
    #include <vtkVersionMacros.h> // For version macros

    int main(int, char *[])
    {
      // Generate a 10 x 10 grid of points
      vtkSmartPointer<vtkPoints> points =
        vtkSmartPointer<vtkPoints>::New();
      for(unsigned int x = 0; x < 10; x++)
      {
        for(unsigned int y = 0; y < 10; y++)
        {
          points->InsertNextPoint(x + vtkMath::Random(-.25, .25),
                                  y + vtkMath::Random(-.25,.25),
                                  0);
        }
      }

      vtkSmartPointer<vtkPolyData> aPolyData =
        vtkSmartPointer<vtkPolyData>::New();
      aPolyData->SetPoints(points);

      // Create a cell array to store the polygon in
      vtkSmartPointer<vtkCellArray> aCellArray =
        vtkSmartPointer<vtkCellArray>::New();

      // Define a polygonal hole with a clockwise polygon
      vtkSmartPointer<vtkPolygon> aPolygon =
       vtkSmartPointer<vtkPolygon>::New();

      aPolygon->GetPointIds()->InsertNextId(22);
      aPolygon->GetPointIds()->InsertNextId(23);
      aPolygon->GetPointIds()->InsertNextId(24);
      aPolygon->GetPointIds()->InsertNextId(25);
      aPolygon->GetPointIds()->InsertNextId(35);
      aPolygon->GetPointIds()->InsertNextId(45);
      aPolygon->GetPointIds()->InsertNextId(44);
      aPolygon->GetPointIds()->InsertNextId(43);
      aPolygon->GetPointIds()->InsertNextId(42);
      aPolygon->GetPointIds()->InsertNextId(32);

      aCellArray->InsertNextCell(aPolygon);

      // Create a polydata to store the boundary. The points must be the
      // same as the points we will triangulate.
      vtkSmartPointer<vtkPolyData> boundary =
       vtkSmartPointer<vtkPolyData>::New();
      boundary->SetPoints(aPolyData->GetPoints());
      boundary->SetPolys(aCellArray);

      // Triangulate the grid points
      vtkSmartPointer<vtkDelaunay2D> delaunay =
       vtkSmartPointer<vtkDelaunay2D>::New();
      delaunay->SetInputData(aPolyData);
      delaunay->SetSourceData(boundary);

      // Visualize
      vtkSmartPointer<vtkPolyDataMapper> meshMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      meshMapper->SetInputConnection(delaunay->GetOutputPort());

      vtkSmartPointer<vtkNamedColors> colors =
        vtkSmartPointer<vtkNamedColors>::New();

      vtkSmartPointer<vtkActor> meshActor =
        vtkSmartPointer<vtkActor>::New();
      meshActor->SetMapper(meshMapper);
      meshActor->GetProperty()->EdgeVisibilityOn();
      meshActor->GetProperty()->SetEdgeColor(colors->GetColor3d("Peacock").GetData());
      meshActor->GetProperty()->SetInterpolationToFlat();

      vtkSmartPointer<vtkPolyDataMapper> boundaryMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      boundaryMapper->SetInputData(boundary);

      vtkSmartPointer<vtkActor> boundaryActor =
        vtkSmartPointer<vtkActor>::New();
      boundaryActor->SetMapper(boundaryMapper);
      boundaryActor->GetProperty()->SetColor(colors->GetColor3d("Raspberry").GetData());
      boundaryActor->GetProperty()->SetLineWidth(3);
      boundaryActor->GetProperty()->EdgeVisibilityOn();
      boundaryActor->GetProperty()->SetEdgeColor(1,0,0);
      boundaryActor->GetProperty()->SetRepresentationToWireframe();

      // 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(meshActor);
      renderer->AddActor(boundaryActor);
      renderer->SetBackground(colors->GetColor3d("Mint").GetData());

      // Render and interact
      renderWindow->SetSize(640, 480);
      renderWindow->Render();
      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(ConstrainedDelaunay2D)

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

    add_executable(ConstrainedDelaunay2D MACOSX_BUNDLE ConstrainedDelaunay2D.cxx )

    target_link_libraries(ConstrainedDelaunay2D ${VTK_LIBRARIES})

### Download and Build ConstrainedDelaunay2D

Click here to download ConstrainedDelaunay2D and its CMakeLists.txt file. Once the tarball ConstrainedDelaunay2D.tar has been downloaded and extracted,

    cd ConstrainedDelaunay2D/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:

    ./ConstrainedDelaunay2D

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.