public double getThickness(Vector3D pt, double perlineRandom){
		//compute by pt.y & central.y
				//300nm ~ 2000 nm
				double min = 700;
				double max = 2000;
				double relative = (pt.y - (center.y - radius)) / (radius * 2);
				if(relative < 0) relative = 0;
				if(relative > 1) relative = 1;
				double thickness = (max - min) * (1-relative) + min;
				thickness += 300 * (2 + perlineRandom * 3) * (PerlinNoise.noise(pt.x/8, pt.y/8, pt.z/8));
				return thickness;
	}