Calcula Distancias en PHP

distancia.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; 
      } 
} 
?>