Creating an AR portal

Currently, we have an app that detects horizontal planes and notifies us about the state of the tracking system. Now, we want to create an AR experience where users will tap on the screen to create a portal and, when going through it, see themselves inside a 3D representation of Van Gogh's Bedroom in Arles painting. The following diagram depicts the scene in SceneKit's coordinate system:

 

The scene in the XYZ coordinates

From the user's perspective, we will have a portal with a hole in it, as shown in the previous diagram. The hole will let us see the model in the background, that is, the 3D painting. The portal will not be gray; it will be transparent so that we can see the camera feed instead of the whole 3D painting scene that hides behind it. In this section, we will learn how to make this possible.

For that, we need to add the 3D...