code: def convert_to_ip(self):
          
          if not self.is_data_loaded:
              self._import_data()
          if self.is_ip is False:
              for coll in self._data:
                  coll.convert_to_ip()
          self._is_ip = True
docs: Convert all Data Collections of this EPW object to IP units.
  
          This is useful when one knows that all graphics produced from this
          EPW should be in Imperial units.