计算地球表面2个点之间的距离

据说是从google earth里提取出来的方法，返回的单位（应该）是公里

private static double EARTH_RADIUS = 6378.137;

public static double GetDistance(double lat1, double lng1, double lat2,
			double lng2) {
	double radLat1 = Math.toRadians(lat1);
	double radLat2 = Math.toRadians(lat2);
	double a = radLat1 - radLat2;
	double b = Math.toRadians(lng1) - Math.toRadians(lng2);
	double s = 2 * Math.asin(Math.sqrt(Math.pow(Math.sin(a / 2), 2)
		+ Math.cos(radLat1) * Math.cos(radLat2)
		* Math.pow(Math.sin(b / 2), 2)));
	s = s * EARTH_RADIUS;
	s = Math.round(s * 10000) / 10000;
	return s;
}