How to know if two surface are in the same direction? In my code I creat a Mesh that are composed by multiple tile. those tile can have edge that are shared, and I need to know if the normal of the tile that have shared edge have the same direction, because I calculat the normal of the edge to smooth the light. before I used the Vector.Dot() , but I've sometimes two tile that have a curve that make impossible to use this function as you can see in the 4th image. and the only information that i have in the calcul is the 2 normal of the tile. img 1 diferent direction img 2 diferent direction img 3 same direction img 4 same direction img 5 same direction