def normalize(self):
        """
        Shift actor's center of mass at origin and scale its average size to unit.
        """
        cm = self.centerOfMass()
        coords = self.coordinates()
        if not len(coords):
            return
        pts = coords - cm
        xyz2 = np.sum(pts * pts, axis=0)
        scale = 1 / np.sqrt(np.sum(xyz2) / len(pts))
        t = vtk.vtkTransform()
        t.Scale(scale, scale, scale)
        t.Translate(-cm)
        tf = vtk.vtkTransformPolyDataFilter()
        tf.SetInputData(self.poly)
        tf.SetTransform(t)
        tf.Update()
        return self.updateMesh(tf.GetOutput())
Shift actor's center of mass at origin and scale its average size to unit.