Cesium高度解析

var viewer = new Cesium.Viewer('cesiumContainer', {
    shadows : true
});
//为true时，球体会有高程遮挡效果（在没有地形时候也会有高程遮挡效果）
viewer.scene.globe.depthTestAgainstTerrain = true;

var viewModel = {
    height: 0
};

Cesium.knockout.track(viewModel);
//获取左上角的toolbar
var toolbar = document.getElementById('toolbar');
Cesium.knockout.applyBindings(viewModel, toolbar);
//添加 3D Tiles，url是路径
var tileset = new Cesium.Cesium3DTileset({ url: Cesium.IonResource.fromAssetId(3883) });
//tileset的根已经准备就绪
tileset.readyPromise.then(function(tileset) {
    //在场景添加tileset
    viewer.scene.primitives.add(tileset);
    //zoomTo （target，offset）目标和偏移
    viewer.zoomTo(tileset, new Cesium.HeadingPitchRange(0.0, -0.5, tileset.boundingSphere.radius * 2.0));
}).otherwise(function(error) {
    //若没有加载成功，提示错误
    console.log(error);
});

Cesium.knockout.getObservable(viewModel, 'height').subscribe(function(height) {
    height = Number(height);
    if (isNaN(height)) {
        return;
        }
//地理位置
    var cartographic = Cesium.Cartographic.fromCartesian(tileset.boundingSphere.center);
    var surface = Cesium.Cartesian3.fromRadians(cartographic.longitude, cartographic.latitude, 0.0);
    var offset = Cesium.Cartesian3.fromRadians(cartographic.longitude, cartographic.latitude, height);
    var translation = Cesium.Cartesian3.subtract(offset, surface, new Cesium.Cartesian3());
    tileset.modelMatrix = Cesium.Matrix4.fromTranslation(translation);
});