title: iOS SceneKit to UIView projection issue
body: <p>I have a SCNView with SCNNode of SCNPlane geometry in front of my camera root node. </p>
  
  <p>Over SCNView, in UIView, I am adding UIImages (Markers) - orange circles.</p>
  
  <p>In Motion listener I am trying to position the Markers in a way so they will stick to the center of each edge of the Plane.</p>
  
  <p>A proper Markers alignment - while device is in straight position:
  <a href="https://i.stack.imgur.com/byNbj.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/byNbj.jpg" alt="A proper Markers alignment - while device is in straight position"></a></p>
  
  <p>I'm doing this using projection from SceneKit objects to UIView:</p>
  
  <pre><code>//world coordinates
  let v1w =  sm.node.convertPosition(sm.node.boundingBox.min, 
      to: self.sceneView.scene?.rootNode)
  let v2w =  sm.node.convertPosition(sm.node.boundingBox.max, 
      to: self.sceneView.scene?.rootNode)
  
  //projected coordinates
  let v1p = self.sceneView.projectPoint(v1w)
  let v2p = self.sceneView.projectPoint(v2w)
  
  //frame rectangle
  let rect = CGRect.init(x: CGFloat(v1p.x), y: CGFloat(v2p.y), 
      width: CGFloat(v2p.x - v1p.x), height: CGFloat(v1p.y - v2p.y))
  
  var frameOld = sm.marker.frame
  
  switch sm.position
  {
  case .Top:
      frameOld.origin.y = rect.minY - frameOld.size.height/2
      frameOld.origin.x = rect.midX - frameOld.size.width/2
  case .Bottom:
      frameOld.origin.y = rect.maxY - frameOld.size.height/2
      frameOld.origin.x = rect.midX - frameOld.size.width/2
  case .Left:
      frameOld.origin.y = rect.midY - frameOld.size.height/2
      frameOld.origin.x = rect.minX - frameOld.size.width/2
  case .Right:
      frameOld.origin.y = rect.midY - frameOld.size.height/2
      frameOld.origin.x = rect.maxX - frameOld.size.width/2
  }
  
  sm.marker.frame = frameOld
  self.view.layoutSubviews()
  </code></pre>
  
  <p>Similar approach you can find here: <a href="https://stackoverflow.com/questions/30758831/scene-kit-projectpoint-calculated-is-displaced">Scene Kit: projectPoint calculated is displaced</a></p>
  
  <p>So I would like those Markers to stick to the edges of the Plane during device motion. But there is the issue: when rotating device - Markers are drifting from the Plane edges
  <a href="https://i.stack.imgur.com/BDfIw.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/BDfIw.jpg" alt="When rotating device - Markers are drifting from the Plane edges"></a></p>
  
  <p>See video of an issue: <a href="https://youtu.be/XBgNDDX5ZI8" rel="nofollow noreferrer">https://youtu.be/XBgNDDX5ZI8</a></p>
  
  <p>I have created a basic project on github to reproduce an issue: <a href="https://github.com/mgontar/SceneKitProjectionIssue" rel="nofollow noreferrer">https://github.com/mgontar/SceneKitProjectionIssue</a></p>