HELPPPPPPPPPPP 
OK… so… i made a scene… looks good. I am happy with it. Its an AR scene. When I open the AR app… it all works and everything but the problem is that even though I added collsions to the model and also tried using blocking volumes that when I open the app and walk around the camera goes through the buildings etc. I have tried several different things. Dont ask what… I played about with the collision settings but it just keeps walking through 