title: How to project a point to screen coordinates from an arbitrary point of view in SceneKit
body: <p>For the purposes of lining up a UIView overlay and some SceneKit objects I need to project some SceneKit world coordinates to 2D view coordinates.</p>
  
  <p>The wrinkle is that the UIView fades in as the camera is moving to its final position, and therefore if I use <code>[view projectPoint:]</code> I get the wrong answer because it is projected from the camera's current position, rather than its final position.</p>
  
  <p>First: have I missed some obvious built-in method that will let me project from an arbitrary point?</p>
  
  <p>Second: if not, how can I create a custom <code>projectPoint</code> method that operates from an arbitrary point of view?</p>
  
  <p>Promising leads seem to be <code>GLKMatrix4MultiplyAndProjectVector3</code> and SCNCamera's <code>projectionTransform</code>, but so far I haven't been able to put these together in a way that produces a sensible answer.</p>