相机追赶的实现（第三人称相机）

var relativeCameraOffset = new THREE.Vector3(0,50,200);
var cameraOffset = relativeCameraOffset.applyMatrix4( MovingCube.matrixWorld );
camera.position.x = cameraOffset.x;
camera.position.y = cameraOffset.y;
camera.position.z = cameraOffset.z;
camera.lookAt( MovingCube.position );

原理是通过物体的矩阵，计算出相机的相对位置，并将相机的朝向指向物体

FYI:
https://stemkoski.github.io/Three.js/Chase-Camera.html