title: Scene Kit: projectPoint calculated is displaced
body: <p>I am trying do draw an frame over a sphere on the parent view of the scene, but for some reason the points converted by <code>SCNScene.projectPoint</code> method are displaced.</p>
  
  <p>To make it simple, i created a sphere at the center of the scene with 2 radius. The sphere is attached to the root node, so top left corner on world coordinates is at (-2,-2,0) point. </p>
  
  <p>Here the complete code:</p>
  
  <pre><code>func sphereWithFrame(){
  
      var v1 = SCNVector3(x: 0,y: 0,z: 0)
      var v2 = SCNVector3(x: 0,y: 0,z: 0)
  
      let topSphere = SCNSphere(radius: 2.0)
      topSphere.firstMaterial!.diffuse.contents = UIColor.greenColor()
  
  
      let topSphereNode = SCNNode(geometry: topSphere)
      topSphereNode.position = SCNVector3Make(0, 0, 0)
      scene.rootNode.addChildNode(topSphereNode)
  
      topSphereNode.getBoundingBoxMin(&amp;v1, max: &amp;v2)
  
      //world coordinates
      let v1w =  topSphereNode.convertPosition(v1, toNode: scene.rootNode)
      let v2w =  topSphereNode.convertPosition(v2, toNode: scene.rootNode)
  
      //projected coordinates
      let v1p = scnview.projectPoint(v1w)
      let v2p = scnview.projectPoint(v2w)
  
      //frame rectangle
      var rect = CGRectMake(CGFloat(v1p.x), CGFloat(v2p.y), CGFloat(v2p.x - v1p.x), CGFloat(v1p.y - v2p.y))
      let rectView = UIView(frame: rect)
      rectView.alpha = 0.3
      rectView.backgroundColor = UIColor.blueColor()
      scnview.addSubview(rectView)
  
      println("v1 \(v1.toString()), v2\(v2.toString())")
      println("v1w \(v1w.toString()), v2w\(v2w.toString())")
      println("v1p \(v1p.toString()), v2w\(v2p.toString())")
      println("rect\(rect)")
  
  }
  </code></pre>
  
  <p>The console:</p>
  
  <pre><code>v1 x:-2.0,y:-2.0,z:-2.0, v2x:2.0,y:2.0,z:2.0
  v1w x:-2.0,y:-2.0,z:-2.0, v2wx:2.0,y:2.0,z:2.0
  v1p x:90.718,y:309.282,z:0.925926, v2wx:263.923,y:136.077,z:0.883838
  rect(90.718, 136.077, 173.205, 173.205)
  </code></pre>
  
  <p>The result on screen is a rectangle a little to the up right from where should be.
  <img src="https://i.stack.imgur.com/KwL7u.png" alt="The result on screen"></p>
  
  <p>I try to follow the post "
  <a href="https://stackoverflow.com/questions/22925879/how-do-i-find-my-mouse-point-in-a-scene-using-scenekit">How do I find my mouse point in a scene using SceneKit?</a>".
  What am i getting wrong?</p>