title: Create objects with ground plane detection only once with Vuforia & Unity
body: <p>I am trying to create an AR app using Unity &amp; Vuforia. I have a 3D model that needs to be spawned when ground plane is detected.But this needs to happen only once.
  The way Vuforia work is, it keeps on spawning objects when new plane is detected. So what i need to do is either detect plane only once or spawn the object only once. As i am new to Unity, i need help doing this. Great if someone could tell me what i need to do to achieve this.</p>