code: function(dx, dy) {
          OpenLayers.Layer.prototype.moveByPx.apply(this, arguments);
          
          if (this.dragPanMapObject) {
              this.dragPanMapObject(dx, -dy);
          } else {
              this.moveTo(this.map.getCachedCenter());
          }
      }
docs: Method: moveByPx
  Move the layer based on pixel vector. To be implemented by subclasses.
  
  Parameters:
  dx - {Number} The x coord of the displacement vector.
  dy - {Number} The y coord of the displacement vector.