code: def unique_str(self):
          
  
          unique_str = "_".join(["%.3f" % f for f in self.geotransform] +
                                ["%d" % d for d in self.x_size, self.y_size]
                                )
          if self.date is not None:
              unique_str += '_' + str(self.date)
          if self.time is not None:
              unique_str += '_' + str(self.time)
          return unique_str.replace(':', '_')
docs: A string that (ideally) uniquely represents this GC object. This
          helps with naming files for caching. 'Unique' is defined as 'If
          GC1 != GC2, then GC1.unique_str() != GC2.unique_str()'; conversely,
          'If GC1 == GC2, then GC1.unique_str() == GC2.unique_str()'.
  
          The string should be filename-safe (no \/:*?"<>|).
  
          ..note::Because of length/readability restrictions, this fxn ignores
          wkt.
  
          Example output:
          "-180.000_0.250_0.000_90.000_0.000_-0.251_512_612_2013-05-21_12_32_52.945000"