Calculate distance between coordinates

distance.php

function distance($lat1, $lon1, $lat2, $lon2, $unit) { 
  $theta = $lon1 - $lon2; 
  $dist = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) +  cos(deg2rad($lat1)) * 
    cos(deg2rad($lat2)) * cos(deg2rad($theta)); 
  $dist = acos($dist);
  $dist = rad2deg($dist);
  $miles = $dist * 60 * 1.1515;

  $unit = strtoupper($unit);

  if ($unit == "K") {

    return ($miles * 1.609344); 

  } else if ($unit == "N") {
      return ($miles * 0.8684);
  } else {
        return $miles;
  }
}