PHP根据经纬度计算距离

/**
     * 根据经纬度算距离，返回结果单位是公里，先纬度，后经度
     * @param $lat1
     * @param $lng1
     * @param $lat2
     * @param $lng2
     * @return float|int
     */
    public function GetDistance($lat1, $lng1, $lat2, $lng2)
    {
        $EARTH_RADIUS = 6378.137;

        $radLat1 = $this->rad($lat1);
        $radLat2 = $this->rad($lat2);
        $a = $radLat1 - $radLat2;
        $b = $this->rad($lng1) - $this->rad($lng2);
        $s = 2 * asin(sqrt(pow(sin($a / 2), 2) + cos($radLat1) * cos($radLat2) * pow(sin($b / 2), 2)));
        $s = $s * $EARTH_RADIUS;
        $s = round($s * 10000) / 10000;

        return $s;
    }

    private function rad($d)
    {
        return $d * M_PI / 180.0;
    }