获取polygon中心点

let f = gisMap.transformFeatureFromWkt(item.the_geom);
          let extent = []
          if(item.the_geom.indexOf('MULTI')>-1){
            extent = boundingExtent(f.getGeometry().getCoordinates()[0][0]);
          } else {
            extent = boundingExtent(f.getGeometry().getCoordinates()[0]);
          }
          let centerP = getCenter(extent);   //获取边界区域的中心位置
          let feature2 = {
            geometry: "POINT(" + centerP[0] + " " + centerP[1] + ")",
            attributes: item,
            style: {
              scale: 0.2,
              src: this.centerDkIcon,
            },
          };
          gisMap.addIcon(feature2);