How can I transition the space from AR to VR like how its done in the tango welcome app ?
The floor can still be found dynamically but how does the app transition into and out of the video overlay ?
Any virtual objects you draw will be drawn "over" the video overlay. You can animate the stencil buffer to achieve a similar effect to what is done in the welcome app.
http://answers.unity3d.com/questions/590800/how-to-cullrender-to-through-a-window.html