    source_obb_tree = vtkOBBTree()
    source_obb_tree.SetDataSet(source)
    source_obb_tree.SetMaxLevel(1)
    source_obb_tree.BuildLocator()

    target_obb_tree = vtkOBBTree()
    target_obb_tree.SetDataSet(target)
    target_obb_tree.SetMaxLevel(1)
    target_obb_tree.BuildLocator()

    source_landmarks = vtkPolyData()
