function  openWindow(Adresse, name, width, height, extras) {
  var MeinFenster = window.open(Adresse, name, "width="+width+",height="+height+",left="+Math.round((screen.availWidth-width)/2)+",top="+Math.round((screen.availHeight-height)/2)+extras);
  MeinFenster.focus();
  return MeinFenster;
}

function Stadtplan() {
	openWindow('stadtplan.html', "stadtplan", 800, 600, ',scrollbars=no');
}