title: How to merge two geometries or meshes using three.js r71?
body: <p>Here I bumped to the problem since I need to merge two geometries (or meshes) to one. Using the earlier versions of three.js there was a nice function:</p>
  
  <pre><code>THREE.GeometryUtils.merge(pendulum, ball);
  </code></pre>
  
  <p>However, it is not on the new version anymore.</p>
  
  <p>I tried to merge <code>pendulum</code> and <code>ball</code> with the following code:</p>
  
  <p><code>ball</code> is a mesh.</p>
  
  <pre><code>var ballGeo = new THREE.SphereGeometry(24,35,35);
  var ballMat = new THREE.MeshPhongMaterial({color: 0xF7FE2E}); 
  var ball = new THREE.Mesh(ballGeo, ballMat); 
  ball.position.set(0,0,0);
  
  var pendulum = new THREE.CylinderGeometry(1, 1, 20, 16);
  ball.updateMatrix();
  pendulum.merge(ball.geometry, ball.matrix);
  scene.add(pendulum);
  </code></pre>
  
  <p>After all, I got the following error:</p>
  
  <pre><code>THREE.Object3D.add: object not an instance of THREE.Object3D. THREE.CylinderGeometry {uuid: "688B0EB1-70F7-4C51-86DB-5B1B90A8A24C", name: "", type: "CylinderGeometry", vertices: Array[1332], colors: Array[0]…}THREE.error @ three_r71.js:35THREE.Object3D.add @ three_r71.js:7770(anonymous function) @ pendulum.js:20
  </code></pre>