void ClickCallbackFunction ( vtkObject* caller, long unsigned int eventId, void* clientData, void* callData );
ElectrodeDetectorPlugin::ElectrodeDetectorPlugin(QVTKWidget *p): QObject(){
    m_InputData                =    vtkSmartPointer <vtkPolyData> :: New();
    m_InputDataActor        =    vtkSmartPointer <vtkActor> :: New();

    m_MaximaData           =    vtkSmartPointer<vtkPolyData>::New();
    m_InputMaximaActor            =    vtkSmartPointer<vtkActor>::New();

    vtkSmartPointer<MouseInteractorStyle1> style  =   vtkSmartPointer<MouseInteractorStyle1>::New(); // Style 1 for manipulation Spin/Pan etc.
    vtkSmartPointer<MouseInteractorStyle2> style  =   vtkSmartPointer<MouseInteractorStyle2>::New();
    ... ....
    renderWindow->GetInteractor()->SetInteractorStyle( style );
   vtkSmartPointer<vtkCallbackCommand> clickCallback = vtkSmartPointer<vtkCallbackCommand>::New(); clickCallback->SetCallback ( ClickCallbackFunction );   renderWindowInteractor->AddObserver ( vtkCommand::LeftButtonPressEvent, clickCallback );

}
void ClickCallbackFunction ( vtkObject* vtkNotUsed(caller), long unsigned int vtkNotUsed(eventId), void* vtkNotUsed(clientData), void* vtkNotUsed(callData) ) { std::cout << "Click callback" << std::endl;

  // Get the interactor like this:
  vtkRenderWindowInteractor *iren =
  static_cast<vtkRenderWindowInteractor*>(caller);

  HERE I need to operations on m_InputData, m_MaximaData using PointPicker Methods
  I also want to draw objects etc.

}