// To setup the ContourWidget and its representation:
#include <vtkContourWidget.h>
#include <vtkProperty.h>
#include <vtkOrientedGlyphContourRepresentation.h>
// To create the geometry:
#include <vtkPolyData.h>
#include <vtkCellArray.h>
#include <vtkPoints.h>
#include <vtkMath.h>
// Usual VTK pipeline elements:
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkInteractorStyleTrackballCamera.h>int main( int argc, char *argv[] )
{// Create the contour widgetvtkSmartPointer<vtkContourWidget> contourWidget = vtkSmartPointer<vtkContourWidget>::New();// Override the default representation for the contour widget to customize its lookvtkSmartPointer<vtkOrientedGlyphContourRepresentation> contourRepresentation =vtkSmartPointer<vtkOrientedGlyphContourRepresentation>::New();contourRepresentation->GetLinesProperty()->SetColor(1, 0, 0); // Set color to redcontourWidget->SetRepresentation(contourRepresentation);// Generate a set of points arranged in a circleint numPts = 10;vtkSmartPointer<vtkPoints> points = vtkSmartPointer<vtkPoints>::New();for (int i = 0; i < numPts; i++){// Create numPts points evenly spread around a circumference of radius 0.1const double angle = 2.0*vtkMath::Pi()*i/numPts;points->InsertPoint(static_cast<vtkIdType>(i), 0.1*cos(angle), 0.1*sin(angle), 0.0 );}// Create a cell array to connect the points into meaningful geometryvtkIdType* vertexIndices = new vtkIdType[numPts+1];for (int i = 0; i < numPts; i++) { vertexIndices[i] = static_cast<vtkIdType>(i); }// Set the last vertex to 0; this means the last line segment will join the 19th point (vertices[19])// with the first one (vertices[0]), thus closing the circle.vertexIndices[numPts] = 0;vtkSmartPointer<vtkCellArray> lines = vtkSmartPointer<vtkCellArray>::New();lines->InsertNextCell(numPts+1, vertexIndices);// Create polydata to hold the geometry just created, and populate itvtkSmartPointer<vtkPolyData> polydata = vtkSmartPointer<vtkPolyData>::New();polydata->SetPoints(points);polydata->SetLines(lines);// Create the renderer to visualize the scenevtkSmartPointer<vtkRenderer> renderer =  vtkSmartPointer<vtkRenderer>::New();renderer->SetBackground(0.1, 0.2, 0.4);            // Set a dark blue background (default is black)// Create the GUI window to hold the rendered scenevtkSmartPointer<vtkRenderWindow> renderWindow =   vtkSmartPointer<vtkRenderWindow>::New();renderWindow->AddRenderer(renderer);// Create the events manager for the renderer windowvtkSmartPointer<vtkRenderWindowInteractor> interactor = vtkSmartPointer<vtkRenderWindowInteractor>::New();interactor->SetRenderWindow(renderWindow);// Use the "trackball camera" interactor style, rather than the default "joystick camera"vtkSmartPointer<vtkInteractorStyleTrackballCamera> style = vtkSmartPointer<vtkInteractorStyleTrackballCamera>::New();interactor->SetInteractorStyle(style);// Set up the contour widget within the visualization pipeline just assembledcontourWidget->SetInteractor(interactor);contourWidget->On();                           // Turn on the interactor observercontourWidget->Initialize(polydata);std::cout << "the number of nodes is " << contourRepresentation->GetNumberOfNodes() << std::endl;// you can get node world position of one node by GetNthNodeWorldPosition(pointID, double_pos[3]) renderer->ResetCamera();                      // Reposition camera to fit the scene elementsinteractor->Initialize();// Start the interactioninteractor->Start();return EXIT_SUCCESS;
}