本篇主要内容为

1. 介绍使用GeoJsonDataSource加载GeoJSON数据之后的代码调用和业务逻辑
2. 从中提炼对polygon进行解析和创建entity的函数以供参考
   • 读取GeoJSON
   • 获取 feature
   • 判断是 Polygon or MultiPolygon
   • 带 hole
   • 创建entity对象

代码调用栈

• Cesium.GeoJsonDataSource.load(data, options)
  • new GeoJsonDataSource().load(data, options) // 创建GeoJsonDataSource对象 并加载数据
    • fun preload(that, data, options, clear) // 调用外部函数进行预加载
      • promise = data.fetchJson() // 使用Cesium.Resource.fetchJson函数读取数据 返回一个promise
      • fun load // 调用外部函数load进行数据加载
        • fun tryHander // 根据输入的数据类型获取对应的处理函数
          • fun processFeatureCollection
            • fun processFeature
              • fun processMultiPolygon
              • fun processPolygon
              • fun processMultiLineString
              • fun processLineString
              • fun processmultiPoint
              • fun processPoint
              • fun processTopology

解析Polygon&创建Entity

1. 读取geojson文件 并返回promise

const jsonPromise = new Cesium.Resource.fetchJson({url: "../../SampleData/data.geojson"
})

2. 解析数据中的polygon 并返回entities对象

// 根据经度、纬度、高度计算得到空间笛卡尔坐标
function crsFunction(coordinates) {return new Cesium.Cartesian3.fromDegrees(coordinates[0], coordinates[1], coordinates[2]);
};// 将经度、纬度、高度数组转换为空间笛卡尔坐标数组
function coordinatesArrayToCartesianArray(coordinates, crsFunction) {const positions = new Array(coordinates.length);for (let i = 0; i < coordinates.length; i++) {positions[i] = crsFunction(coordinates[i]);}return positions;
}// 根据多边形创建对应的entity         
function createPolygonEntity(polygon){const holes = [];// 如果为带洞多边形for (let i = 1, len = polygon.length; i < len; i++) {holes.push(new Cesium.PolygonHierarchy(coordinatesArrayToCartesianArray(polygon[i], crsFunction)));}// 返回可用于创建entity的object对象return {polygon: {hierarchy:new Cesium.PolygonHierarchy(coordinatesArrayToCartesianArray(polygon[0], crsFunction),holes),height: 0,material: Cesium.Color.RED.withAlpha(0.5),outline: true,outlineColor: Cesium.Color.BLACK,},id: Cesium.createGuid()}
}// 解析GeoJSON数据并返回用于创建entity的object
function getEntitiesFromGeoJSON(data){const entities = []data.features.forEach(feature => {// 获取每个feature的坐标信息和多边形类型const polygons = feature.geometry.coordinates;const polygonType = feature.geometry.type;// 对多边形和多多边形进行分别处理if (polygonType == "Polygon"){const entity = createPolygonEntity(polygons);entities.push(entity);} else if (polygonType == "MultiPolygon"){for (let i = 0; i < polygons.length; i++) {const entity = createPolygonEntity(polygons[i]);entities.push(entity);}}})return entities;
}jsonPromise.then(function(data){const entities = getEntitiesFromGeoJSON(data);
})

3. 添加所有entity对象

entities.forEach(function(entity){viewer.entities.add(entity)
})