Google map api distance vol d oiseau

function get_distance_m($lat1, $lng1, $lat2, $lng2) {
  $earth_radius = 6378137;   // Terre = sphère de 6378km de rayon
  $rlo1 = deg2rad($lng1);
  $rla1 = deg2rad($lat1);
  $rlo2 = deg2rad($lng2);
  $rla2 = deg2rad($lat2);
  $dlo = ($rlo2 - $rlo1) / 2;
  $dla = ($rla2 - $rla1) / 2;
  $a = (sin($dla) * sin($dla)) + cos($rla1) * cos($rla2) * (sin($dlo) * sin($dlo));
  $d = 2 * atan2(sqrt($a), sqrt(1 - $a));
  return ($earth_radius * $d);
}

flightPlanCoordinates = [ 
        new google.maps.LatLng(37.772323, -122.214897), 
        new google.maps.LatLng(21.291982, -157.821856)];

function get_figthPlan(dest) {   
  geocoder = new google.maps.Geocoder();   
  geocoder.geocode( { 'address': dest}, function(results, status) {   
                             /* Si l'adresse a pu être géolocalisée */   
                             if (status == google.maps.GeocoderStatus.OK) {   
              /* Récupération de sa latitude et de sa longitude */   
                                 flightPlanCoordinates.push(results[0].geometry.location);   
                                  }   
              });   
  }