獲取GPS 兩點間的直線距離

private static double Distance(double long1, double lat1, double long2,
			double lat2) {
		double a, b, R;
		R = 6378137; // 地球半徑
		lat1 = lat1 * Math.PI / 180.0;
		lat2 = lat2 * Math.PI / 180.0;
		a = lat1 - lat2;
		b = (long1 - long2) * Math.PI / 180.0;
		double d;
		double sa2, sb2;
		sa2 = Math.sin(a / 2.0);
		sb2 = Math.sin(b / 2.0);
		d = 2
				* R
				* Math.asin(Math.sqrt(sa2 * sa2 + Math.cos(lat1)
						* Math.cos(lat2) * sb2 * sb2));
		return d;
	}