I had a similar problem also with my scripts. I wanted to simply know if a Point was behind a Line or not...

 
/*-----------------------------------------------------------------
Returns true if Point P is behind line defined by Points C and D.
 ----------------------------------------------------------------*/
function isBehindLine(P:Point,C:Point,D:Point):Boolean
{
	var a:Number=Point.distance(P,C.add(Point.polar(1,Math.atan2(C.y - D.y,C.x - D.x) + Math.PI / 2)));
	var b:Number=Point.distance(P,C.add(Point.polar(-1,Math.atan2(C.y - D.y,C.x - D.x) + Math.PI / 2)));
	return a < b;
}