code: function (viewPortPx) {
          var lonlat = null; 
          if (this.baseLayer != null) {
              lonlat = this.baseLayer.getLonLatFromViewPortPx(viewPortPx);
          }
          return lonlat;
      }
docs: TRANSLATION: LonLat <-> ViewPortPx  
  Method: getLonLatFromViewPortPx
  
  Parameters:
  viewPortPx - {<OpenLayers.Pixel>|Object} An OpenLayers.Pixel or
  an object with a 'x'
  and 'y' properties.
  
  Returns:
  {<OpenLayers.LonLat>} An OpenLayers.LonLat which is the passed-in view
  port <OpenLayers.Pixel>, translated into lon/lat
  by the current base layer.