###数据库的一种写法

$lat="24.88718";
$lng="118.60347";
$fujin=\think\Db::name("zhiyuan")
        ->field("warehouseName,lat,lng,
        (  3959 * acos (cos ( radians({$lat}) ) * cos( radians( lat ) ) * cos( radians( lng ) - radians({$lng}) )  + sin ( radians({$lat}) )  * sin( radians( lat ) )  )  
        ) AS distance")
       ->order("distance asc")
       ->select();

###函数写法

/**单位为米

 * @param $lat1

 * @param $lon1

 * @param $lat2

 * @param $lon2

 * @param float $radius  星球半径 公里

 * @return float

 */

function distance($lat1, $lon1, $lat2,$lon2,$radius = 6378.137)

{

    $rad = floatval(M_PI / 180.0);




    $lat1 = floatval($lat1) * $rad;

    $lon1 = floatval($lon1) * $rad;

    $lat2 = floatval($lat2) * $rad;

    $lon2 = floatval($lon2) * $rad;
    $theta = $lon2 - $lon1;
     $dist = acos(sin($lat1) * sin($lat2) +
     cos($lat1) * cos($lat2) * cos($theta)
 );




    if ($dist < 0 ) {

        $dist += M_PI;

    }

    $dist = $dist * $radius;

    return round($dist,2);

}