function gmap_routenplaner(frm) {

      var start, ziel, uri;

      fields = Array('fromstreet', 'fromplz', 'fromcity');
      msg    = Array('Straße', 'PLZ', 'Ort');

      for(i=0; i < fields.length; i++) {

         if(frm.elements[fields[i]]) {

            if(!frm.elements[fields[i]].value) {
              alert("Bitte füllen Sie das Feld '" + msg[i] + "' aus!");
              frm.elements[fields[i]].focus();
              return false;
            }

         }

      }

      start  = document.getElementsByName("fromstreet")[0].value + ",+";
      start += document.getElementsByName("fromplz")[0].value + "+";
      start += document.getElementsByName("fromcity")[0].value;

      ziel  = document.getElementsByName("tostreet")[0].value + ",+";
      ziel += document.getElementsByName("toplz")[0].value + "+";
      ziel += document.getElementsByName("tocity")[0].value;

      uri = frm.action + '&saddr=' + start + '&daddr=' + ziel;

      open(uri, 'gmap_routenplaner', 'width=900,height=700,resizable=yes');

      return false;
   }