add point to index, point must be a GeoPoint instance
        :param point:
        :return:

def add_point(self, point):
        """
        add point to index, point must be a GeoPoint instance
        :param point:
        :return:
        """
        assert isinstance(point, GeoPoint), \
            'point should be GeoPoint instance'
        point_hash = self.get_point_hash(point)
        points = self.data.setdefault(point_hash, [])
        points.append(point)