:returns: opposite vertices of the bounding prism for this 
            object.
        :rtype: ndarray([min], [max])

def get_domain(self):
        """
        :returns: opposite vertices of the bounding prism for this 
            object.
        :rtype: ndarray([min], [max])
        """
        if self.domain is None:
            return np.array([self.points.min(axis=0), 
                             self.points.max(axis=0)])
        return self.domain