code: def is_valid(self):
          
          if len(self.geometry) == 0:
              return True
  
          try:
              referenced = {self.graph[i][1]
                            for i in self.graph.nodes_geometry}
          except BaseException:
              # if connectivity to world frame is broken return false
              return False
  
          # every geometry is referenced
          ok = referenced == set(self.geometry.keys())
  
          return ok
docs: Is every geometry connected to the root node.
  
          Returns
          -----------
          is_valid : bool
            Does every geometry have a transform