svg转geojson，ceisum 加载geojson,webgl 加载geojson数据没有贴地

我有一份geojson数据：

const smc={"type":"FeatureCollection", "features": [

svg转geojson，{"type":"Feature","geometry":{"type":"Polygon","coordinates":[[[119.66253898412081,30.368448359079963],[119.66243188888996,30.368413407509607],[119.66239524553978,30.368497829777414],[119.662502340849,30.36853278137794],[119.66253898412081,30.368448359079963]]]},"properties":{"OBJECTID":1,"Shape_Leng":42.0000000005,"Shape_Area":110.000000003,"FWMC":"混","FWCS":"3","YSDM":"141161","X":119.662467115,"Y":30.3684730944}}

]}

使用Cesium.GeoJsonDataSource加载并且想使数据在地形之上，但是我加载之后数据在地形影像下面，按照官网设置了clampToGround为true也没生效，请问有遇到过这个问题吗？要怎么解决呢？

我的代码如下：

const smcPromise = Cesium.GeoJsonDataSource.load(smc,

{

clampToGround: true

}

);

smcPromise.then(dataSource => {

viewer.dataSources.add(dataSource);

const entities = dataSource.entities.values;

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

var entity = entities[i];

entity.$name = "smc";

var color = (color = Cesium.Color.fromRandom({

alpha: 1.0

}));

entity.polygon.material = color;

entity.polygon.outline = false;

entity.polygon.extrudedHeight = 10.0;

}

viewer.flyTo(smcPromise);

});