cesium 模型随地图缩放

以下是cesium模型随地图缩放的代码实现：

// 获取当前场景
var scene = viewer.scene;

// 获取当前相机
var camera = viewer.camera;

// 获取当前地图中心点
var center = camera.pickEllipsoid(new Cesium.Cartesian2(viewer.canvas.clientWidth / 2, viewer.canvas.clientHeight / 2));

// 监听地图缩放事件
viewer.scene.postRender.addEventListener(function() {
    // 获取当前地图中心点
    var newCenter = camera.pickEllipsoid(new Cesium.Cartesian2(viewer.canvas.clientWidth / 2, viewer.canvas.clientHeight / 2));
    if (newCenter) {
        // 计算缩放比例
        var height = scene.globe.getHeight(newCenter);
        var distance = Cesium.Cartesian3.distance(camera.position, newCenter);
        var pixelSize = scene.globe.ellipsoid.cartesianToCartographic(newCenter).height / viewer.canvas.clientHeight;
        var scale = distance / pixelSize / height;

        // 计算缩放中心点
        var centerScratch = new Cesium.Cartesian3();
        var centerRay = camera.getPickRay(new Cesium.Cartesian2(viewer.canvas.clientWidth / 2, viewer.canvas.clientHeight / 2));
        var centerPosition = scene.globe.pick(centerRay, scene);
        if (centerPosition) {
            Cesium.Cartesian3.fromRadians(centerPosition.longitude, centerPosition.latitude, height, scene.globe.ellipsoid, centerScratch);
        }

        // 设置缩放中心点和缩放比例
        camera.lookAt(centerScratch, new Cesium.HeadingPitchRange(camera.heading, camera.pitch, scale));
    }
});

以上代码实现了监听地图缩放事件，获取当前地图中心点，计算缩放比例，计算缩放中心点，设置缩放中心点和缩放比例的功能，从而实现了cesium模型随地图缩放的效果。