code: function() {
          if (!this.center && this.size) {
              this.center = this.getLonLatFromViewPortPx({
                  x: this.size.w / 2,
                  y: this.size.h / 2
              });
          }
          return this.center;
      }
docs: Method: getCachedCenter
  
  Returns:
  {<OpenLayers.LonLat>}