code: function(evt) {
          var pos = OpenLayers.Util.pagePosition(this.map.viewPortDiv);
          evt.xy.x -= pos[0];
          evt.xy.y -= pos[1];
      }
docs: Method: adjustXY
  Converts event coordinates that are relative to the document body to
  ones that are relative to the map viewport. The latter is the default in
  OpenLayers.
  
  Parameters:
  evt - {Object}