Plane Equation

Note that if, for a given [x y z], Ax + By + Cz + D = 0, then 2Ax + 2By + 2Cz + 2D = 0, and in general:

        NAx + NBy + NCz + ND = 0

In other words, multiplying the four coefficients by the same constant N will still define the same plane.

However, the value of NAx + NBy + NCz + ND will be N times the value of Ax + By + Cz + D. This is useful in texture coordinate generation.