效果图:

let center = this.cube.position.clone(),
　　size = this.cube.geometry.boundingBox.getSize(),
　　scale = this.cube.scale;

let heightStr = "长度:" + (size.y * scale.y).toFixed(2),
　 widthStr = "宽度:" + (size.x * scale.x).toFixed(2);
 
let canvas = document.createElement("canvas");
canvas.width = 200;
canvas.height = 100
let context =canvas.getContext("2d");
context.font = "Bold 40px Georgia";
context.fillStyle = "#ffffff";
context.fillText(heightStr, 0, 40);
context.fillText(widthStr, 0, 90);
let spritelTexture = new THREE.Texture(canvas);
spritelTexture.needsUpdate = true;
let spriteMaterial = new THREE.SpriteMaterial({ map: spritelTexture });
let spritel = new THREE.Sprite(spriteMaterial);
spritel.scale.set(5, 2.5, 1);
spritel.position.set(center.x + 3, center.y - 2, center.z);
this.scene.scene.add(spritel);