Example of PHP calculation of the maximum and minimum longitude and latitude of 4 corners within 3 kilometers of the current coordinates

The example in this article describes the PHP method of calculating the maximum and minimum longitude and latitude of 4 corners within 3 kilometers of the current coordinates. Share it with everyone for your reference, the details are as follows:

//$lng 、$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)
);

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