We've discussed what augmented reality is, but how does it work? As we said earlier, AR requires that we combine the real environment with a computer-generated virtual environment. The graphics are registered to the real 3D world. And, this must be done in real time.

There are a number of ways to accomplish this. In this book, we will consider just two. The first is the most common and accessible method: using a handheld mobile device such as a smartphone or tablet. Its camera captures the environment, and the computer graphics are rendered on the device's screen.

A second technique, using wearable AR smartglasses, is just emerging in commercial devices, such as Microsoft HoloLens and Metavision's Meta 2. This is an optical see-through of the real world, with computer graphics shown on a wearable near-eye display.