8 18 12 GtsSurface GtsFace GtsEdge GtsVertex
1 -1 -1
1 1 -1
1 1 1
1 -1 1
-1 -1 1
-1 -1 -1
-1 1 1
-1 1 -1
1 2
3 2
1 3
4 3
1 4
5 4
5 3
6 1
6 4
3 7
7 5
6 5
6 8
8 5
7 8
2 8
6 2
2 7
1 2 3
3 4 5
6 4 7
8 5 9
7 10 11
9 6 12
13 12 14
14 11 15
13 16 17
16 15 18
17 1 8
18 10 2