地图偏移量以及计算距离函数

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

public static double GetDistance(double lat1, double lng1, double lat2, double lng2) {
    double radLat1 = rad(lat1);
    double radLat2 = rad(lat2);
    double a = radLat1 - radLat2;
    double b = rad(lng1) - rad(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 * 6378.137;
    s = Math.round(s * 10000) / 10000;
    return s;
}