title: How to add a shadow plane and the difference between the .scn file apple provide and we create
body: <p>In the .scn file I created for my project using Xcode, the file looks like this (the missile file included in the attachments) in the perspective view.  But in the .scn model that apple provide in the ARKit example project, the plane and file looks far more different. It has a shadow plane and the view also looks entirely different. So my question is,
  1. How do I add a shadow plane in my file and what is the use of it.
  2. What is the difference between the two files. The one apple provides me and the one I created.
  3. The best practices for creating an AR application.</p>
  
  <p><strong><em>1.The image Apple provides</em></strong>
  <img src="https://i.stack.imgur.com/dlZwa.png" alt="1.The image Apple provides,"></p>
  
  <p><strong><em>2.The file I created (source: turbosquid.com)</em></strong></p>
  
  <p><img src="https://i.stack.imgur.com/2yy0h.png" alt="2.The file I created (source: turbosquid.com)">
  thank you</p>