docs: function(olZoom) {
          var zoom = null; 
          if (olZoom != null) {
              zoom = olZoom + this.minZoomLevel;
              if (this.map.baseLayer !== this) {
                  zoom = this.getZoomForResolution(
                      this.map.baseLayer.getResolutionForZoom(zoom)
                  );
              }
          }
          return zoom;
      }