As we've seen and discussed, the essence of AR is that your device recognizes objects in the real world and renders the computer graphics registered to the same 3D space, providing the illusion that the virtual objects are in the same physical space with you.

Since augmented reality was first invented decades ago, the types of targets the software can recognize has progressed from very simple markers for images and natural feature tracking to full spatial map meshes. There are many AR development toolkits available; some of them are more capable than others of supporting a range of targets.

The following is a survey of various target types. We will go into more detail in later chapters, as we use different targets in different projects.