PHP计算两个坐标的直线距离

if (!function_exists('get_distance')){
    /**
     * 计算两个坐标的直线距离
     */
    function get_distance($lat1, $lng1, $lat2, $lng2){
        $earthRadius = 6378138; //近似地球半径米
        // 转换为弧度
        $lat1 = ($lat1 * pi()) / 180;
        $lng1 = ($lng1 * pi()) / 180;
        $lat2 = ($lat2 * pi()) / 180;
        $lng2 = ($lng2 * pi()) / 180;
        // 使用半正矢公式  用尺规来计算
        $calcLongitude = $lng2 - $lng1;
        $calcLatitude = $lat2 - $lat1;
        $stepOne = pow(sin($calcLatitude / 2), 2) + cos($lat1) * cos($lat2) * pow(sin($calcLongitude / 2), 2);
        $stepTwo = 2 * asin(min(1, sqrt($stepOne)));
        $calculatedDistance = $earthRadius * $stepTwo;
        return round($calculatedDistance);
    }

}