
272 Virtual Reality: Concepts and Technologies
The number of objects present as well as the precision required for selecting them
are factors that increase the complexity of the task that we wish to accomplish.
• characteristics of users: level of experience, learning ability, imagination...
On this basis, the first aim regarding manipulation in virtual environments is to let
the user accomplish two basic tasks: selection and manipulation. Selection is the des-
ignation of one or more objects in the virtual universe for future use. Manipulation is
the modification of properties of one or more objects, most often of the position and
orientation, but ...