Augmented Reality was proposed in 1994 by Milgram et al.
[1], in which the Reality Virtuality Continuum theory is used to
define clearly the difference between the Augmented Reality
and virtual reality. As shown in Figure 1, they designed a scale
between the reality and virtual environment where these two
subjects located on the very end position of the scale. The
middle of the scale is called the ’mixed reality’. The one closer
to the real environment is called the Augmented Reality, while
the other one closer to the virtual environment is known as the
Augmented Virtuality.