Lecture 9: Ray Tracing (19)

The idea behind this is because the surface normal is by definition perpendicular to the surface, and the resulting vector of v=ppv = p - p' where pp' is any point on the plane is a vector in the plane. All vectors in the plane must be perpendicular to the surface normal, meaning that their dot product is 0 (since cos(90) = 0).

You must be enrolled in the course to comment