Here''s the problem. I first had my 3d points and I needed to find the intersection polygon between a square polygon and a triangle polygon. So the easiest way to do that is using 2d points instead of 3d, since the triangle and square were on the same plane. So I used the tangent vector and binormal and did this: out.x = Dot(tangent, point); out.y = Dot(binormal, point); that worked well. But now that I have my new 2d points how could I convert them back to 3d if I have the tangent, binormal and normal information? Thanks.