php根据经度纬度计算距离

/**
     * 经度维度的计算连点的距离
     * @param  $d
     */
private function rad($d) {
        return $d * 3.1415926535898 / 180.0;
    }
    private function GetDistance($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;
    }