The angle between a line, r, and a plane, π, is the angle between r and its orthogonal projection onto π, r'.
That is, the angle between a line and a plane is equal to the complementary acute angle that forms between the direction vector of the line and the normal vector of the plane.
Let's name θ to the angle which line makes with plane, u=(u1,u2,u3) the direction vector of line and n=(A,B,C) the normal vector of the plane.
