code: def segment(self):
          
          # half the height
          half = self.primitive.height / 2.0
          # apply the transform to the Z- aligned segment
          points = np.dot(
              self.primitive.transform,
              np.transpose([[0, 0, -half, 1], [0, 0, half, 1]])).T[:, :3]
          return points
docs: A line segment which if inflated by cylinder radius
          would represent the cylinder primitive.
  
          Returns
          -------------
          segment : (2, 3) float
            Points representing a single line segment