# Delaunay2D

VTKExamples/Cxx/Filtering/Delaunay2D

### Description

This example generates a set of points aligned with an XY grid with random heights (z values). The Delaunay2D filter "magically" knows how to triangulate this type of point set because it projects the points by default onto the XY axis and then performs a 2D Delaunay triangulation. The result is a mesh on the input points.

Other Languages

See (Python), (Java)

### Code

Delaunay2D.cxx

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

    #include <vtkCellArray.h>
    #include <vtkPoints.h>
    #include <vtkTriangle.h>
    #include <vtkPolyData.h>
    #include <vtkPointData.h>
    #include <vtkLine.h>
    #include <vtkCellLocator.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkActor.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkProperty.h>
    #include <vtkVertexGlyphFilter.h>
    #include <vtkNamedColors.h>

    int main(int, char *[])
    {
      // Create a set of heighs on a grid.
      // This is often called a "terrain map".
      vtkSmartPointer<vtkPoints> points =
        vtkSmartPointer<vtkPoints>::New();

      unsigned int GridSize = 10;
      for(unsigned int x = 0; x < GridSize; x++)
      {
        for(unsigned int y = 0; y < GridSize; y++)
        {
            points->InsertNextPoint(x, y, (x+y)/(y+1));
        }
      }

      // Add the grid points to a polydata object
      vtkSmartPointer<vtkPolyData> polydata =
        vtkSmartPointer<vtkPolyData>::New();
      polydata->SetPoints(points);

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

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

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

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

      vtkSmartPointer<vtkVertexGlyphFilter> glyphFilter =
        vtkSmartPointer<vtkVertexGlyphFilter>::New();
      glyphFilter->SetInputData(polydata);

      vtkSmartPointer<vtkPolyDataMapper> pointMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      pointMapper->SetInputConnection(glyphFilter->GetOutputPort());

      vtkSmartPointer<vtkActor> pointActor =
        vtkSmartPointer<vtkActor>::New();
      pointActor->GetProperty()->SetColor(colors->GetColor3d("Tomato").GetData());
      pointActor->GetProperty()->SetPointSize(5);
      pointActor->SetMapper(pointMapper);

      vtkSmartPointer<vtkRenderer> renderer =
        vtkSmartPointer<vtkRenderer>::New();
      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->AddRenderer(renderer);
      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      renderWindowInteractor->SetRenderWindow(renderWindow);

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

      renderWindow->Render();
      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(Delaunay2D)

    find_package(VTK COMPONENTS
      vtkCommonColor
      vtkCommonCore
      vtkCommonDataModel
      vtkFiltersCore
      vtkFiltersGeneral
      vtkInteractionStyle
      vtkRenderingCore
      vtkRenderingFreeType
      vtkRenderingOpenGL2 QUIET)
    if (NOT VTK_FOUND)
      message("Skipping Delaunay2D: ${VTK_NOT_FOUND_MESSAGE}")
      return ()
    endif()
    message (STATUS "VTK_VERSION: ${VTK_VERSION}")
    if (VTK_VERSION VERSION_LESS "8.90.0")
      # old system
      include(${VTK_USE_FILE})
      add_executable(Delaunay2D MACOSX_BUNDLE Delaunay2D.cxx )
      target_link_libraries(Delaunay2D PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(Delaunay2D MACOSX_BUNDLE Delaunay2D.cxx )
      target_link_libraries(Delaunay2D PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS Delaunay2D
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build Delaunay2D

Click here to download Delaunay2D and its CMakeLists.txt file. Once the tarball Delaunay2D.tar has been downloaded and extracted,

    cd Delaunay2D/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:

    ./Delaunay2D

WINDOWS USERS

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