php求出当前坐标 3公里内4个角落的最大最小经纬度

$lng 、$lat 经纬度//

$half = 6371;

$distance = 3; //3公里

$dlng = 2 * asin(sin($distance / (2 * $half)) / cos(deg2rad($lat)));

$dlng = rad2deg($dlng);

$dlat = $distance / $half;

$dlat = rad2deg($dlat);

$fourpoint = array(

'left-top' => array('lat' => $lat + $dlat, 'lng' => $lng - $dlng),

'right-top' => array('lat' => $lat + $dlat, 'lng' => $lng + $dlng),

'left-bottom' => array('lat' => $lat - $dlat, 'lng' => $lng - $dlng),

'right-bottom' => array('lat' => $lat - $dlat, 'lng' => $lng + $dlng)

);