docs: function (lonlat, resolution) {
          var px = null; 
          if (lonlat != null) {
              resolution = resolution || this.map.getResolution();
              var extent = this.map.calculateBounds(null, resolution);
              px = new OpenLayers.Pixel(
                  (1/resolution * (lonlat.lon - extent.left)),
                  (1/resolution * (extent.top - lonlat.lat))
              );    
          }
          return px;
      }