code: def facets_on_hull(self):
          
          # facets plane, origin and normal
          normals = self.facets_normal
          origins = self.facets_origin
  
          # (n,3) convex hull vertices
          convex = self.convex_hull.vertices.view(np.ndarray).copy()
  
          # boolean mask for which facets are on convex hull
          on_hull = np.zeros(len(self.facets), dtype=np.bool)
  
          for i, normal, origin in zip(range(len(normals)), normals, origins):
              # a facet plane is on the convex hull if every vertex
              # of the convex hull is behind that plane
              # which we are checking with dot products
              dot = np.dot(normal, (convex - origin).T)
              on_hull[i] = (dot < tol.merge).all()
  
          return on_hull
docs: Find which facets of the mesh are on the convex hull.
  
          Returns
          ---------
          on_hull : (len(mesh.facets),) bool
            is A facet on the meshes convex hull or not