使用cesium和threejs加载3d模型，详细源码

以下是一个使用Cesium和Three.js加载3D模型的示例代码：

// 创建Cesium Viewer
var viewer = new Cesium.Viewer("cesiumContainer");

// 创建Three.js场景
var scene = new THREE.Scene();

// 创建Three.js渲染器
var renderer = new THREE.WebGLRenderer({
  alpha: true,
  antialias: true,
});
renderer.setSize(viewer.canvas.clientWidth, viewer.canvas.clientHeight);
renderer.setPixelRatio(window.devicePixelRatio);
renderer.gammaInput = true;
renderer.gammaOutput = true;
renderer.gammaFactor = 2.2;
renderer.shadowMap.enabled = true;

// 将Three.js渲染器添加到Cesium场景中
var csRenderer = new THREE.CSS3DRenderer();
csRenderer.setSize(viewer.canvas.clientWidth, viewer.canvas.clientHeight);
csRenderer.domElement.style.position = "absolute";
csRenderer.domElement.style.top = 0;
document.getElementById("cesiumContainer").appendChild(csRenderer.domElement);

// 创建Three.js相机并将其添加到Cesium场景中
var camera = new THREE.PerspectiveCamera(
  45,
  viewer.canvas.clientWidth / viewer.canvas.clientHeight,
  0.1,
  1000
);
var csCamera = new THREE.PerspectiveCamera(
  45,
  viewer.canvas.clientWidth / viewer.canvas.clientHeight,
  0.1,
  1000
);
viewer.scene.primitives.add(new Cesium.Primitive({}));

// 创建Three.js灯光并将其添加到Cesium场景中
var light = new THREE.DirectionalLight(0xffffff, 1);
light.position.set(0, 1, 1);
scene.add(light);

// 加载模型
var loader = new THREE.GLTFLoader();
loader.load(
  "models/model.gltf",
  function (gltf) {
    // 获取模型并将其添加到Three.js场景中
    var model = gltf.scene;
    model.scale.set(0.5, 0.5, 0.5);
    scene.add(model);

    // 将模型添加到Cesium场景中
    var csModel = new THREE.CSS3DObject(model);
    csModel.position.set(0, 0, 0);
    csRenderer.render(scene, camera);
    viewer.scene.primitives.add(csModel);

    // 监听Cesium相机变化并更新Three.js相机
    viewer.camera.changed.addEventListener(function () {
      camera.position.copy(viewer.camera.position);
      camera.position.y += 15;
      camera.lookAt(scene.position);
      renderer.render(scene, camera);
      csCamera.position.copy(viewer.camera.position);
      csCamera.position.y += 15;
      csCamera.lookAt(scene.position);
      csRenderer.render(scene, csCamera);
    });
  },
  undefined,
  function (error) {
    console.error(error);
  }
);

这段代码首先创建了一个Cesium Viewer，然后创建了一个Three.js场景和一个Three.js渲染器。接着将Three.js渲染器添加到Cesium场景中，并创建了一个Three.js相机并将其添加到Cesium场景中。然后创建了一个Three.js灯光并将其添加到Cesium场景中。最后加载了一个模型，并将其添加到Three.js场景中和Cesium场景中。监听了Cesium相机的变化，并更新了Three.js相机的位置和方向。