def translate_z(self, d):
        """Translate mesh for z-direction

        :param float d: Amount to translate
        """
        mat = numpy.array([
            [1, 0, 0, 0],
            [0, 1, 0, 0],
            [0, 0, 1, 0],
            [0, 0, d, 1]
        ])
        self.vectors = self.vectors.dot(mat)
        return self