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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);

}