cesium 给polygon添加label

cesium 中的polygon本身是无法获取中心点坐标，不支持添加label，但是往往业务需求都需要添加标注，下面提供一种解决方案：

var sectorEntity = sectorCollection.add({
                                name: name,
                                id:"azimuth-"+id,
                                polygon: {
                                    hierarchy: Cesium.Cartesian3.fromDegreesArrayHeights(tirangleCoords),
                                    material: Cesium.Color.LIGHTSKYBLUE,
                                    perPositionHeight: true
                                },
                                sectorId:id,
                                station_x:sector.X,
                                station_y:sector.Y,
                                //stationId:baseStationId,
                                //bsType:bsType
                            });

                            var ploy = Cesium.Cartesian3.fromDegreesArrayHeights(tirangleCoords);
                            var polyCenter = Cesium.BoundingSphere.fromPoints(ploy).center;

                            sectorCollection.add({
                                position:polyCenter,
                                label: {

                                    text: reslabel,

                                    // font: '20px Helvetica',
                                    //fillColor : Cesium.Color.SKYBLUE,
                                    //outlineColor: Cesium.Color.BLACK,
                                    //outlineWidth: 2,

                                    showBackground: false,

                                    // backgroundColor: Cesium.Color.LIME,

                                    //style: Cesium.LabelStyle.FILL_AND_OUTLINE,

                                    // outlineWidth: 1,


                                    horizontalOrigin: Cesium.HorizontalOrigin.LEFT,

                                    verticalOrigin: Cesium.VerticalOrigin.BOTTOM,
                                    heightReference:Cesium.HeightReference.RELATIVE_TO_GROUND,

                                    //pixelOffset: new Cesium.Cartesian2(0.0, -25),

                                    //pixelOffsetScaleByDistance : new Cesium.NearFarScalar(1.5e2, 3.0, 1.5e7, 0.5)
                                    scaleByDistance :new Cesium.NearFarScalar(200, 3, 900, 0.0)

                                }
                            });

以polygon的坐标计算中心点坐标，创建label实体