public static double getAngle(double x1, double y1, double x2, double y2)
	{
		double deltaX = x2-x1;
		double deltaY = y2-y1;
		double result = Math.atan2(deltaX, deltaY);
		result = -result+0.5*Math.PI;
		if(result>Math.PI)
			result = -Math.PI + (result-Math.PI);
		return result;
	}