code: function (bounds) {
          bounds = this.adjustBounds(bounds);
          var zoom = this.getZoom();
          var extent = this.map.getMaxExtent();
          var deg = this.lzd/Math.pow(2,this.getZoom());
          var x = Math.floor((bounds.left - extent.left)/deg);
          var y = Math.floor((bounds.bottom - extent.bottom)/deg);
          if (this.map.getResolution() <= (this.lzd/512)
              && this.getZoom() <= this.zoomLevels) {
              return this.getFullRequestString(
                { L: zoom, 
                  X: x,
                  Y: y
                });
          } else {
              return OpenLayers.Util.getImageLocation("blank.gif");
          }
  
      }
docs: Method: getURL
  
  Parameters:
  bounds - {<OpenLayers.Bounds>}
  
  Returns:
  {String} A string with the layer's url and parameters and also the
  passed-in bounds and appropriate tile size specified as
  parameters