Tracking a user's motion and ultimately their position in 2D and 3D space is fundamental to any AR application. ARCore allows us to track position changes by identifying and tracking visual feature points from the device's camera image. An example of how this works is shown in this figure:

In the figure, we can see how the user's position is tracked in relation to the feature points identified on the real couch. Previously, in order to successfully track motion (position), we needed to pre-register or pre-train our feature points. If you have ever used the Vuforia AR tools, you will be very familiar with having to train images or target markers. Now, ARCore does all this automatically for us, in real time, without any training. However, this tracking technology is very new and has several limitations. In the later part of the book, and specifically in Chapter 5, Real-World Motion Tracking, we will add a feature to our AR assistant that allows us to track multiple objects' positions from multiple devices in real time using GPS. Then, in Chapter 10, Mixing in Mixed Reality, we will extend our tracking to include augmented maps.