# TriangleArea

VTKExamples/Cxx/PolyData/TriangleArea

### Code

TriangleArea.cxx

    #include <vtkSmartPointer.h>
    #include <vtkCellArray.h>
    #include <vtkPoints.h>
    #include <vtkPolyData.h>
    #include <vtkTriangle.h>

    int main(int, char *[])
    {
      //setup points (geometry)
      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 a triangle on the three points in the polydata
      vtkSmartPointer<vtkTriangle> triangle1 =
        vtkSmartPointer<vtkTriangle>::New();
      triangle1->GetPointIds()->SetId ( 0, 0 );
      triangle1->GetPointIds()->SetId ( 1, 1 );
      triangle1->GetPointIds()->SetId ( 2, 2 );

      vtkSmartPointer<vtkTriangle> triangle2 =
        vtkSmartPointer<vtkTriangle>::New();
      triangle2->GetPointIds()->SetId ( 0, 2 );
      triangle2->GetPointIds()->SetId ( 1, 3 );
      triangle2->GetPointIds()->SetId ( 2, 0 );

      //add the triangles to the list of triangles
      vtkSmartPointer<vtkCellArray> triangles =
        vtkSmartPointer<vtkCellArray>::New();
      triangles->InsertNextCell ( triangle1 );
      triangles->InsertNextCell ( triangle2 );

      //create a polydata object
      vtkSmartPointer<vtkPolyData> polydata =
        vtkSmartPointer<vtkPolyData>::New();

      //add the geometry and topology to the polydata
      polydata->SetPoints ( points );
      polydata->SetPolys ( triangles );

      for(vtkIdType i = 0; i < polydata->GetNumberOfCells(); i++)
      {
        vtkCell* cell = polydata->GetCell(0);

        vtkTriangle* triangle = dynamic_cast<vtkTriangle*>(cell);
        double p0[3];
        double p1[3];
        double p2[3];
        triangle->GetPoints()->GetPoint(0, p0);
        std::cout << "p0: " << p0[0] << " " << p0[1] << " " << p0[2] << std::endl;
        triangle->GetPoints()->GetPoint(1, p1);
        std::cout << "p1: " << p1[0] << " " << p1[1] << " " << p1[2] << std::endl;
        triangle->GetPoints()->GetPoint(2, p2);
        std::cout << "p2: " << p2[0] << " " << p2[1] << " " << p2[2] << std::endl;

        double area = vtkTriangle::TriangleArea(p0, p1, p2);

        std::cout << "area of triangle " << i << ": " << area << std::endl;
      }
      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(TriangleArea)

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

    add_executable(TriangleArea MACOSX_BUNDLE TriangleArea.cxx )

    target_link_libraries(TriangleArea ${VTK_LIBRARIES})

### Download and Build TriangleArea

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

    cd TriangleArea/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:

    ./TriangleArea

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.