ARKit doesn’t require this. Instead, it recognizes planes, like your floor. Then it uses the phone’s camera and its motion detectors to track movement as the iPhone is moved and tilted.
Motion co-processors like the iPhone 7 Plus’s M10 can efficiently track data from the gyroscope, accelerometer, and magnetometer. This lets it monitor movement in a 3D space without excessive hardware demands. Google has actually announced something similar too, called ARCore. It’s Project Tango for phones without the flashy camera tech
The core of ARKit is about letting you drop objects into an environment and manipulate them using the touchscreen. Other than recognizing real-world objects, the main aim is to keep track of objects as the iPhone is moved. As soon as it loses track of this, the illusion is shattered.
One of the most obvious uses for this is interior design. You could place a chair in the corner of the room, and see how it looks as you turn the phone for a different view. It is like a more advanced version of some online glasses retailers’ virtual try-on feature.