code: function Plane3D( a , b , c , d ) {
  	var self = Object.create( Plane3D.prototype ) ;
  
  	self.normal = new Vector3D( a , b , c ) ;
  	self.d = + d ;
  	self.normalizeCheck() ;
  
  	return self ;
  }
docs: /*
  This is the equation using the normal:
  vx * X + vy * Y + vz * Z + D = 0
  where D = - px * vx - py * vy - pz * vz