[vtkusers] Problem with getting pointId after Picking operation!!!

[Łukasz Tutaj]

Hi vtk Users,

    In my work display medical images (DICOM). I want to choose a point 
on a screen and then I want to get pointId of this point. I use in this 
case vtkPointPicker.I have a problem in getting pointId after picking 
operation. I always get pointId = -1. However some pick event take place 
because I get good coordinates of event position. I don't know what is 
wrong. In my opinion this piece of code I have written should work. But 
it doesn't. Could someone look at it and tell me what is wrong? Please.
Here is this code.

class vtkMyCallback : public vtkCommand
{
public:
    int x, y;
  static vtkMyCallback *New() { return new vtkMyCallback; }
  virtual void Execute(vtkObject *caller, unsigned long, void*)
    {
      vtkRenderWindowInteractor *iren = 
reinterpret_cast<vtkRenderWindowInteractor*>(caller);
            x = iren->GetEventPosition()[0];
            y = iren->GetEventPosition()[1];
            vtkPointPicker *picker = (vtkPointPicker *)iren->GetPicker();
            int pointId = picker->GetPointId();
            cout << "(" << x << ", " << y << ") " << pointId << endl;
    }
};

int main()
{
    vtkRenderer *ren = vtkRenderer::New();
    vtkRenderWindow *renwin = vtkRenderWindow::New();
    renwin->AddRenderer(ren);

    vtkRenderWindowInteractor *iren = vtkRenderWindowInteractor::New();
    iren->SetRenderWindow(renwin);
   
    vtkDICOMImageReader *reader = vtkDICOMImageReader::New();
    reader->SetFileName("D:\\PRACA MAGISTERSKA\\dane381\\46009361");

    vtkImageMapper *mapper = vtkImageMapper::New();
    mapper->SetInput(reader->GetOutput());
    mapper->SetColorWindow(300);
    mapper->SetColorLevel(40);
    vtkActor2D *actor = vtkActor2D::New();
    actor->SetMapper(mapper);
    ren->AddActor2D(actor);
    renwin->SetSize(512,512);
    renwin->Render();

    vtkPointPicker *picker = vtkPointPicker::New();
    picker->SetTolerance(0.00001);
    iren->SetPicker(picker);

    vtkMyCallback *mo1 = vtkMyCallback::New();
    iren->AddObserver(vtkCommand::EndPickEvent,mo1);

    iren->Start();

    iren->RemoveObserver(mo1);
 
    iren->Initialize();
    iren->Start();

    mo1->Delete();
    ...
    ....
    return 0;
}