code: function( wmsBaseUrl, queryOptions ) {
  		var bbox = queryOptions.bbox;
  		if ( typeof bbox !== 'string' ) {
  			bbox = this.extentToBbox( bbox.minx,
  				bbox.miny,
  				bbox.maxx,
  				bbox.maxy );
  			delete queryOptions.bbox;
  		}
  		queryOptions = extend( {
  			request: 'GetMap',
  			version: this.version,
  			service: 'wms',
  			format: 'image/png',
  			styles: '',
  			width: '256',
  			height: '256',
  			bbox: bbox
  		}, queryOptions );
  		var url = new urijs( wmsBaseUrl ).addQuery( queryOptions );
  		return url.toString();
  	}
docs: Formats an URL to include specific GET parameters
  required for a GetMap WMS method request
  @param {String} mwsBaseUrl. URL of the WMS Service endpoint
  @param {Object} QueryOptions
  - {String} layers. comma separated Layers names
  - {String|Object} bbox. Bounding box as string (commas eparated values)
  or as an objext with keys minx,miny,maxx,maxy