vtk中长度测量和角度测量

注意：使用QVTKWidget时不要使用vtkSmartPointer

长度测量：

demo：https://lorensen.github.io/VTKExamples/site/Cxx/Widgets/DistanceWidget/

  vtkSmartPointer<vtkDistanceWidget> distanceWidget =
    vtkSmartPointer<vtkDistanceWidget>::New();
  distanceWidget->SetInteractor(renderWindowInteractor);
  distanceWidget->CreateDefaultRepresentation();
  static_cast<vtkDistanceRepresentation *>(distanceWidget->GetRepresentation())
    ->SetLabelFormat("%-#6.3g mm");

  // Render an image (lights and cameras are created automatically)
  renderWindow->Render();

  renderWindowInteractor->Initialize();
  renderWindow->Render();
  distanceWidget->On();

角度测量：

demo1：https://lorensen.github.io/VTKExamples/site/Cxx/Widgets/AngleWidget/
demo2：https://lorensen.github.io/VTKExamples/site/Cxx/Widgets/AngleWidget2D/

  vtkSmartPointer<vtkAngleWidget> angleWidget = 
    vtkSmartPointer<vtkAngleWidget>::New();
  angleWidget->SetInteractor(renderWindowInteractor);
  angleWidget->CreateDefaultRepresentation();

  // Render
  renderWindow->Render();
  renderWindowInteractor->Initialize();
  renderWindow->Render();
  angleWidget->On();
  renderWindowInteractor->Start();