function popUp(url, breite, hoehe) {
  // Errechnet Koordinaten, um das Popup zentriert zu platzieren
  links = (screen.width/2)-(breite/2);
  oben = (screen.height/2)-(hoehe/2);
  window.open(url,"popup","height="+hoehe+",width="+breite+",status=no,toolbar=no,menubar=no,location=no,resizable=yes,titlebar=no,scrollbars=yes,fullscreen=no,top ="+oben+",left ="+links);
}