Normals and Plane Equations
Need normals for shading, plane eqns for intersection tests
A normal to a plane is a vector that is perpendicular to that plane (two possible choices)
A plane is specified by a point P and a normal vector N
N•(X-P) = 0 if and only if X lies in the plane; this is an implicit equation for the plane
- Expand this out: 0 = N•X - N•P = ax + by + cz + d
3 vertices define a plane, its normal is: N=(B-A) x (C-A)