docs: def convert(self, root_cls):
          """Convert to another derived class. cls is the base class for the derived type,
          ie AcsGeoid, TigerGeoid, etc. """
  
          d = self.__dict__
          d['sl'] = self.sl
  
          try:
              cls = root_cls.get_class(root_cls.sl)
          except (AttributeError, TypeError):
              # Hopefully because root_cls is a module
              cls = root_cls.get_class(self.sl)
  
          return cls(**d)