<?PHP
 
/*::                                                                         :*/
/*::  definitions:                                                           :*/
/*::    south latitudes are negative, east longitudes are positive           :*/
/*::                                                                         :*/
/*::  passed to function:                                                    :*/
/*::    lat1, lon1 = latitude and longitude of point 1 (in decimal degrees)  :*/
/*::    lat2, lon2 = latitude and longitude of point 2 (in decimal degrees)  :*/
/*::    unit = the unit you desire for results                               :*/
/*::           where: 'm' is statute miles                                   :*/
/*::                  'k' is kilometers (default)                            :*/
/*::                  'n' is nautical miles                                  :*/
 
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;
      }
}
 
ECHO distance(32.9697, -96.80322, 29.46786, -98.53506, "m") . " miles<br>";
ECHO distance(32.9697, -96.80322, 29.46786, -98.53506, "k") . " kilometers<br>";
ECHO distance(32.9697, -96.80322, 29.46786, -98.53506, "n") . " nautical miles<br>";
 
?>