Distance from Point (x, y, z) to Plane (ax + by + cz + d = 0)

point_plane_distance.cpp

double Point::distanceTo(Plane p) {
    return abs( p.a * x   + p.b * y   + p.c * z   + p.d) /
	   sqrt(p.a * p.a + p.b * p.b + p.c * p.c);
}