three.js为何坐标轴会有平行的情况

     // 场景和相机
    this.scene = new THREE.Scene();
    this.camera = new THREE.PerspectiveCamera(120, width / height, 0.1, 1000);
    this.camera.position.x = 0;
    this.camera.position.y = 10;
    this.camera.position.z = 0;
    this.camera.lookAt(new THREE.Vector3(10, 10, 10));
    // 坐标轴
    this.scene.add(new THREE.AxisHelper(50));

主要是观察点的问题， this.camera.lookAt(new THREE.Vector3(10, 10, 10));

this.camera.position.y = 10; 与相机Y轴坐标相同，当然后出现平行情况。