if (!is_dir($dir)) return;

    $this->base_dir = $dir;

    $dir_fd = opendir($this->base_dir);

    while (false !== ($file = readdir($dir_fd))) {

       if (preg_match('/(.*)_[0-9]+_[0-9]+_[0-9]+\.jpg$/', $file, $reg)) {

	 $this->prefix = $reg[1];

	 break;

       }

    }

    $pfname = $this->base_dir.'/'.$this->prefix.'.params';

    if (is_file($pfname)) {

      $this->params = @parse_ini_file($pfname);

  }

  public function get_params() {

    return $this->params;

  }

  public function get_name() {

    return basename($this->base_dir);

  }

  public function get_prefix() {

    return $this->prefix;

  }

  public function get_magnifications() {

    $dir_fd = opendir($this->base_dir);

    while (false !== ($file = readdir($dir_fd))) {                // extraction des paramètres de grossissement par le serveur

    $lon2 = $lon * M_PI/180;

    $dLat = $lat2-$lat1;

    $angle = 2 * atan2(sqrt($a), sqrt(1-$a));

    $d = $angle * $rt;                    // distance du point en Kms

    $y = sin($dLon)*cos($lat2);

    $x = cos($lat1)*sin($lat2) - sin($lat1)*cos($lat2)*cos($dLon);

    $cap = atan2($y, $x);                 // cap pour atteindre le point en radians

    $e = atan2(($alt2 - $alt1)/1000 - $d*$d/(2*$rt), $d);  // angle de l'élévation en radians

    //    printf("%s, %s, %s, %s\n",$lat1, $this->params['latitude'], $lat, $dLat);

    return array($d, $cap*180/M_PI, $e*180/M_PI);   // les résultats sont en degrés

  }

}