php calculate distance between two coordinates (longitude, latitude)

php calculates the distance between two coordinates (longitude, latitude), and returns the result as meters or kilometers

function distance($lat1, $lng1, $lat2, $lng2, $miles = true)
{
 $pi80 = M_PI / 180;
 $lat1 *= $pi80;
 $lng1 *= $pi80;
 $lat2 *= $pi80;
 $lng2 *= $pi80;

 $r = 6372.797; // mean radius of Earth in km
 $dlat = $lat2 - $lat1;
 $dlng = $lng2 - $lng1;
 $a = sin($dlat / 2) * sin($dlat / 2) + cos($lat1) * cos($lat2) * sin($dlng / 2) * sin($dlng / 2);
 $c = 2 * atan2(sqrt($a), sqrt(1 - $a));
 $km = $r * $c;

 return ($miles ? ($km * 0.621371192) : $km);
}

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