# PolygonIntersection

VTKExamples/Cxx/GeometricObjects/PolygonIntersection

Other Languages

See (Python), (CSharp)

### Code

PolygonIntersection.cxx

    #include <vtkSmartPointer.h>
    #include <vtkPoints.h>
    #include <vtkPolygon.h>

    int main(int, char*[])
    {
      // Create a square in the XY plane
      vtkSmartPointer<vtkPoints> points = vtkSmartPointer<vtkPoints>::New();
      points->InsertNextPoint(0.0, 0.0, 0.0);
      points->InsertNextPoint(1.0, 0.0, 0.0);
      points->InsertNextPoint(1.0, 1.0, 0.0);
      points->InsertNextPoint(0.0, 1.0, 0.0);

      // Create the polygon
      vtkSmartPointer<vtkPolygon> polygon = vtkSmartPointer<vtkPolygon>::New();
      polygon->GetPoints()->DeepCopy(points);
      polygon->GetPointIds()->SetNumberOfIds(4); // 4 corners of the square
      polygon->GetPointIds()->SetId(0, 0);
      polygon->GetPointIds()->SetId(1, 1);
      polygon->GetPointIds()->SetId(2, 2);
      polygon->GetPointIds()->SetId(3, 3);

      // Inputs
      double p1[3] = {0.1, 0, -1.0};
      double p2[3] = {0.1, 0, 1.0};
      double tolerance = 0.001;
      // Outputs
      double t; // Parametric coordinate of intersection (0 (corresponding to p1) to 1 (corresponding to p2))
      double x[3]; // The coordinate of the intersection
      double pcoords[3];
      int subId;

      vtkIdType iD = polygon->IntersectWithLine(p1, p2, tolerance, t, x, pcoords, subId);

      std::cout << "intersected? " << iD << std::endl;
      std::cout << "intersection: " << x[0] << " " << x[1] << " " << x[2] << std::endl;

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(PolygonIntersection)

    find_package(VTK COMPONENTS
      vtkCommonCore
      vtkCommonDataModel QUIET)
    if (NOT VTK_FOUND)
      message("Skipping PolygonIntersection: ${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(PolygonIntersection MACOSX_BUNDLE PolygonIntersection.cxx )
      target_link_libraries(PolygonIntersection PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(PolygonIntersection MACOSX_BUNDLE PolygonIntersection.cxx )
      target_link_libraries(PolygonIntersection PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS PolygonIntersection
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build PolygonIntersection

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

    cd PolygonIntersection/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:

    ./PolygonIntersection

WINDOWS USERS

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