0 0 z a
0 0 z+1/2 a
0 1/2 z b
0 1/2 z+1/2 b
1/2 0 z c
1/2 0 z+1/2 c
1/2 1/2 z d
1/2 1/2 z+1/2 d
x y z e
-x -y z e
x -y z+1/2 e
-x y z+1/2 e