protected Image createTurtleImage(double dir) {
		int heading = GMath.round(dir / 10);
		if (heading < 0) heading = 36 - (-heading % 36);
		heading %= 36;
		if (turtleImage[heading] == null) {
			turtleImage[heading] = MediaTools.createImage(TURTLE_IMAGE[heading]);
		}
		return turtleImage[heading];
	}