From: Tony Healy Subject: DESIGN: Definitions for Virtual Reality Systems Date: December 28, 1995 From: Tony Healy Definitions for Virtual Reality Systems ======================================= Following on from the contributions of John Costella, John Draper and others, particularly in drawing attention to the difference between what's viewed and how we view it, I present the following set of definitions for this emerging field of virtual reality. I distinguish three parts of a system - how we view something, what we are viewing and how the resulting 2D imagery is presented to us. I seek to include related systems, such as film, into this system of definitions to help differentiate between them when required. I use virtual reality as a broad shorthand term to mean real time 3D systems, but that is not important here. I use precomputed animation to mean a 3D animation rendered over a period of time and captured to film or other file format. List of terms: 1. TYPES OF VIEWING: How we see and experience something Presence Emulation: Active Presence Emulation: Passive Presence Emulation: Passive Presence Emulation With Forking: 2. TYPES OF WORLD: What we see and interact with Virtual World: Mirror World: Snapshot World: 3. TYPES OF PRESENTATION: How the 2D imagery is displayed to us Depth simulation using perspective views: Depth simulation using stereoscopic viewing: Stereoscopic viewing using single screen: Stereoscopic viewing using dual screens: Definitions of terms: 1. TYPES OF VIEWING: How we see and experience something ======================================================== Presence Emulation: Presenting imagery and other sensory information similar to the imagery we would experience if located at the site being simulated. This imagery may be on a screen or in a headset. Presence emulation includes the views we see in films, precomputed animations and telepresence systems, as well as in real time 3D virtual reality. Active Presence Emulation: Presence emulation where we are able to move in the world we're experiencing, and see the results of that movement in real time, and to modify objects in the world we're experiencing, in real time. Active presence emulation includes telepresence systems and real time 3D virtual reality, but not films and precomputed animations. Passive Presence Emulation: Presence emulation where we just experience a view without being able to move in or modify the world. Passive Presence Emulation includes films and precomputed animations, but not telepresence systems and real time 3D virtual reality. Passive Presence Emulation With Forking: Passive presence emulation where we can choose which of two or more alternative pieces of film or animation to view next. It is useful to have this term as a lot of multimedia is termed interactive on the basis of this simple selection capability. It is useful to be able to distinguish this from the more powerful Active Presence Emulation. ( With extensions ) Each of the above terms can take suffixes to describe particular additional sensory information or manipulative capabilities. For example, we can talk of Active Presence Emulation With Directional Audio and Force Feedback. 2. TYPES OF WORLD: What we see and interact with ================================================ Virtual World: A synthetic 3D world, which the user may or may not be able to influence. Virtual worlds include the worlds viewed in real time 3D virtual reality systems and in precomputed animations, but not the worlds viewed in telepresence systems. When a virtual world is experienced using Active Presence Emulation, the resulting combination is a virtual reality system. When experienced using Passive Presence Emulation, the resulting system is probably a precomputed animation (but not necessarily). Mirror World: A representation of an actual world, such as a patient undergoing surgery at a remote location, presented in a telepresence system for the user to take actions in. The mirror world will be slaved to the actual world, so that actions the user takes in the mirror world will be executed in the actual world. Mirror worlds include the worlds in telepresence systems only. Snapshot World: A representation of an actual or virtual world, captured at some point in time as a film or precomputed animation. Snapshot worlds can not be modified, and do not even exist in 3D form, but only in the 2D imagery captured to represent the snapshot. 3. TYPES OF PRESENTATION: How the 2D imagery is displayed to us =============================================================== Depth simulation using perspective views: Creating the illusion of depth by correctly incorporating perspective in the generated views of a scene. Most virtual reality systems do this. Depth simulation using stereoscopic viewing: Creating the illusion of depth by correctly generating the different views from the left and right eyes. Most virtual reality systems do this if they are designed to be viewed using headsets. However if they weren't, then some headsets will display the same image to the left and right eyes. Stereoscopic viewing using single screen: Presenting left and right eye views by having the user wear glasses with different filters in each eye, or by rapidly alternating views on the single screen. This is not considered a powerful way of presenting stereoscopic views, but needs to be defined to distinguish it from conventional stereoscopic viewing. Stereoscopic viewing using dual screens: Presenting left and right eye views, one each to a screen. This is the way stereoscopic views are normally presented. Normally the two screens are eyepieces in a headset. Tony Healy Silicon CHiC