//视图

    var viewer = new Cesium.Viewer('map', {

        animation: false,

        baseLayerPicker: false,

        fullscreenButton: false,

        geocoder: false,

        homeButton: false,

        infoBox: false,

        sceneModePicker: false,

        selectionIndicator: false,

        timeline: false,

        navigationHelpButton: false,

        scene3DOnly: true,

        sceneMode: 3,

        navigationInstructionsInitiallyVisible: false,

        showRenderLoopErrors: false,

        imageryProvider: new Cesium.UrlTemplateImageryProvider({

            url: 'http://www.google.cn/maps/vt?lyrs=s@198&gl=en&x={x}&y={y}&z={z}',

            credit: '',

            tilingScheme: new Cesium.WebMercatorTilingScheme(),

            maximumLevel: 18,

            show: false

        })

    });

//场景

    var scene = viewer.scene;

//隐藏版权信息

    viewer._cesiumWidget._creditContainer.style.display = "none";

//解决图标遮挡

     viewer.scene.globe.depthTestAgainstTerrain = false;

//添加entity

      var entity=viewer.entities.add({

                                id:data.datas[i].site_id,//站点id

                                name:"air",

                                position:Cesium.Cartesian3.fromDegrees(Number(data.datas[i].lng), Number( data.datas[i].lat),0),   

                                billboard:{

                                    // position:Cesium.Cartesian3.fromDegrees(Number(data.datas[i].lat),Number(data.datas[i].lng),10),

                                    verticalOrigin : Cesium.VerticalOrigin.BOTTOM,

                                    image:'../images/marker/house-green1.png'

                                },

                                label: {

                                    text:  data.datas[i].pm25,

                                    font: '14px Helvetica',

                                    showBackground: true,

                                        // backgroundColor: Cesium.Color.LIME,

                                        style: Cesium.LabelStyle.FILL_AND_OUTLINE,

                                        // outlineWidth: 1,

                                        horizontalOrigin: Cesium.HorizontalOrigin.CENTER,

                                        verticalOrigin: Cesium.VerticalOrigin.TOP,

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

                                        pixelOffsetScaleByDistance : new Cesium.NearFarScalar(1.5e2, 3.0, 1.5e7, 0.5)

                                }

                            });       
      viewer.zoomTo(entity);

//移除所有要素

    viewer.entities.removeAll()

//注销掉原来的tileset

    tileset = tileset && tileset.destroy();

//添加Geojson（点）并添加图标

      var promise = Cesium.GeoJsonDataSource.load("../data/point.json");

        promise.then(function (dataSource) {

                viewer.dataSources.add(dataSource);

                var entities = dataSource.entities.values;

                for (var i = 0; i < entities.length; i++) {

                    var entity = entities[i];

                    entity.billboard.image = '../images/marker/house01.png';

                }

      });

//移除全部数据源

      var len = viewer.dataSources.length;

        if(len > 0){

            console.log(len)

            for(var n = 0; n < len; n++){

                //每删除一条viewer.dataSources，len就会减少1

                viewer.dataSources.remove(viewer.dataSources.get(0));

            }

        }

//定位

    viewer.zoomTo(viewer.entities);