def ShowTrihedron(on):
    import libSalomePy
    r = libSalomePy.getRenderer()
    if not r: return
    actors = r.GetActors()
    actors.InitTraversal()
    actor = actors.GetNextActor()
    while actor:
        if actor.GetClassName() in [ "VTKViewer_LineActor", "VTKViewer_UnScaledActor", "vtkFollower" ]:
            actor.SetVisibility(on)
            pass
        actor = actors.GetNextActor()
        pass
    pass