世界坐标系转经纬度坐标系
var ellipsoid=viewer.scene.globe.ellipsoid;
var cartesian3=new Cesium.cartesian3(x,y,z);
var cartographic=ellipsoid.cartesianToCartographic(cartesian3);
var lat=Cesium.Math.toDegrees(cartograhphic.latitude);
var lng=Cesium.Math.toDegrees(cartograhpinc.longitude);
var alt=cartographic.height;