Virtual environment applications use different kinds of control. We often need to stimulate the change of system state, leading to appropriate change of currently running action to another needed at given time. Following real-world metaphor, in VE we must move close to object to be able to interact with it. For example, if we want to manipulate object, that is located out of our reach distance, then at first we must come near to object, to such a distance that allows us to grab object and manipulate it. To facilitate it we have to stop processing of current event and invoke travel action. Similarly we may need to set some other parameters of VE application. It means that besides movement we also have to communicate with VE application (eg. announce that we want to transfer object to a new position).
There are many methods how to control VE-based applications. At present, most of VE applications are controlled via Graphical User Interface (GUI), voice and gesture commands combined with some logical tools. In the following we will adduce the taxonomy of system control techniques and then describe GUI-based methods.