加载geoserver的wms服务图层

      let smart = new Cesium.WebMapServiceImageryProvider({
        url : 'http://localhost:8899/geoserver/one/wms',
        layers : 'one:country',
        parameters : {
          transparent : true, //是否透明
          format : 'image/png',
          srs: 'EPSG:4326',
          styles:''
        }
      });
      this.viewer.imageryLayers.addImageryProvider(smart);