title: ARAnchor for SCNNode
body: <p>I'm trying to get a hold of the anchor after adding an SCNNode to the scene of an ARSCNView. My understanding is that the anchor should be created automatically, but I can't seem to retrieve it.</p>
  
  <p>Below is how I add it. The node is saved in a variable called testNode.</p>
  
  <pre><code>let node = SCNNode()
  node.geometry = SCNBox(width: 0.5, height: 0.1, length: 0.3, chamferRadius: 0)
  node.geometry?.firstMaterial?.diffuse.contents = UIColor.green
  
  sceneView.scene.rootNode.addChildNode(node)
  
  testNode = node
  </code></pre>
  
  <p>Here is how I try to retrieve it. It always prints nil.</p>
  
  <pre><code>if let testNode = testNode {
      print(sceneView.anchor(for: testNode))
  }
  </code></pre>
  
  <p>Does it not create the anchor? If it does: is there another method I can use to retrieve it?</p>