def V(self):
n1,n2,n3,n4 = self.getNodes()
V = np.array([[1, n1.x, n1.y, n1.z],
[1, n2.x, n2.y, n2.z],
[1, n3.x, n3.y, n3.z],
[1, n4.x, n4.y, n4.z]])
return la.det(V)/6