One of the defining features of immersive virtual reality is the ability to interact with objects in the virtual world in a natural manner. However, this metahpor is lacking.
Users can only manipulate objects within the arm's reach.
To grab other objects, some travel technique must be used. Positioning large objects is difficult with this metaphor, since the user must be so close to them. Therefore, other techniques are needed. There are two main categories of techniques. In this metaphor, the user's virtual arm can be extended or retracted to grab or position virtual objects.