Sprite Size

scale

HTML

<script src="https://cdn.rawgit.com/mrdoob/three.js/master/build/three.min.js"></script>
<script src="https://cdn.rawgit.com/mrdoob/three.js/master/examples/js/controls/OrbitControls.js"></script>

CSS

body {
  overflow: hidden;
  margin:0;
  padding: 0;
}

JavaScript

var camera, scene, renderer, controls;
var planets = [];
var timestamp = 0;
var scaleVector = new THREE.Vector3();

init();
animate();

function init() {

  scene = new THREE.Scene();
  camera = new THREE.PerspectiveCamera(90, window.innerWidth / window.innerHeight, 1, 10000);
  camera.position.set(0, 100, 100);

  renderer = new THREE.WebGLRenderer({
    antialias: true
  });
  renderer.setSize(window.innerWidth, window.innerHeight);
  document.body.appendChild(renderer.domElement);

  controls = new THREE.OrbitControls(camera, renderer.domElement);

  var createPlanet = function(name, radius, orbit, speed) {
    var geom = new THREE.SphereGeometry(radius, 32, 16);
    var mat = new THREE.MeshBasicMaterial({
      color: Math.random() * 0xFFFFFF,
    });
    var planet = new THREE.Mesh(geom, mat);
    planet.userData.orbit = orbit;
    planet.userData.speed = speed;

    var canvas = document.createElement('canvas');
    canvas.width = 256;
    canvas.height = 256;

    var tex = new THREE.Texture(canvas);
    tex.needsUpdate = true;
    var spriteMat = new THREE.SpriteMaterial({
      map: tex
    });
    var sprite = new THREE.Sprite(spriteMat);

    planet.add(sprite);
    planets.push(planet);
    scene.add(planet);


  };

  createPlanet("One", 11, -10, 5);
  createPlanet("Two", 11, 5, 5);
  createPlanet("Three", 11, 10, 5);

}

function animate() {
  requestAnimationFrame(animate);
  planets.forEach(function(planet) {
    
    var scaleFactor = 100;
    var scale = scaleVector.subVectors(planet.position, camera.position).length() / scaleFactor;
    planet.scale.set(scale, scale, scale);
    
    var orbit = planet.userData.orbit;
    var speed = planet.userData.speed;
    
    planet.position.x = speed * orbit;
    planet.position.z = speed * orbit;
  });
  render();
}

function render() {
  renderer.render(scene, camera);
}