In 1997 Azuma [2] further proposed the Augmented
Reality by another definition. He states that Augmented Reality
must include three key properties: (1) Combination of real and
virtual (2) Interactivity in real time (3) Registering in 3-D. He
emphasizes that Augmented Reality must be able to operate in
three-dimensional space, and that operators should be able to
interact with the virtual objects in the real environment.
Therefore, in the augmented reality, the three factors, threedimensionality,
real-time, and the virtual reality must coexist.