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