Setting a transformed vertex wouldn't make any sense, because that would mean that you set it in world space. That's basically why the getter exists: To get a vertex' position in world space. It should be possible to add such a method, but i'm not sure if like the idea. That would be two places (PolygonManager and VertexController) for the same thing, with the PolygonManager being simpler to use but slower and the more complicated, but faster, VertexController. I'll think about it...