title: Hide SCNFloor but show shadow with SceneKit (swift)
body: <p>I am trying to display a shadow of my character on a map I have. I have a <em>ambient</em> light and an <em>omni</em> light. If I add a floor, it shows the shadow/reflection, but the floor covers the map.
  <a href="https://i.stack.imgur.com/K3Wfw.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/K3Wfw.png" alt="With Floor"></a></p>
  
  <p>Without a floor, I don't get any shadow/reflection.
  <a href="https://i.stack.imgur.com/zFoM8.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/zFoM8.png" alt="Without Floor"></a></p>
  
  <p>I add floor like this: </p>
  
  <pre><code>floor = SCNFloor()
  floor.reflectionFalloffEnd = 10
  floor.reflectivity = 0.5
  let floorNode = SCNNode(geometry: floor)
  floorNode.position = SCNVector3(x: 0, y: -1.0, z: 0)
  self.rootNode.addChildNode(floorNode)
  </code></pre>
  
  <p>The map is created with Mapbox iOS SDK (MGLMapView).</p>