def _get_centroid_time(self, time_diff):
        """
        Calculates the time difference between the date-time classes
        """
        source_time = datetime.datetime.combine(self.date, self.time)
        second_diff = floor(fabs(time_diff))
        microsecond_diff = int(1000. * (time_diff - second_diff))
        if time_diff < 0.:
            source_time = source_time - datetime.timedelta(
                seconds=int(second_diff), microseconds=microsecond_diff)
        else:
            source_time = source_time + datetime.timedelta(
                seconds=int(second_diff), microseconds=microsecond_diff)
        self.time = source_time.time()
        self.date = source_time.date()
Calculates the time difference between the date-time classes