code: def centroid(self):
          
  
          # use the centroid of each triangle weighted by
          # the area of the triangle to find the overall centroid
          centroid = np.average(self.triangles_center,
                                axis=0,
                                weights=self.area_faces)
          centroid.flags.writeable = False
          return centroid
docs: The point in space which is the average of the triangle centroids
          weighted by the area of each triangle.
  
          This will be valid even for non- watertight meshes,
          unlike self.center_mass
  
          Returns
          ----------
          centroid : (3,) float
            The average vertex weighted by face area