计算两点经纬度之间的算法

	private static final double EARTH_RADIUS = 6378.137;

	private static double rad(double d) {
		return d * Math.PI / 180.0;
	}

	/**
	 * 得出两个经纬度之间的距离
	 * 
	 * @param r_longitude
	 * @param r_latitude
	 * @param n_longitude
	 * @param n_latitude
	 * @return 距离
	 */
	public static double getDistanceByLanLon(double r_longitude,
			double r_latitude, double n_longitude, double n_latitude) {
		double radLat1 = rad(r_latitude);
		double radLat2 = rad(n_latitude);
		double a = radLat1 - radLat2;
		double b = rad(r_longitude) - rad(n_longitude);
		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;
	}