Figure 3 VR Peripheral TechnologiesThe universal input devices for computer based systems, a mouse and keyboard, are almost useless for interaction in a virtual environment. The conventional mouse can be used but it severely restricts the user in a way that reduces the effectiveness of the VR system. A virtual environment provides a true spatial representation of a system and this means that a user should be able to use a device that exhibits at least six degrees of freedom. Analysis of interaction in a virtual environment shows the following types of basic interaction.
Direct Manipulation, Object Pick and Place
This method of interaction has a direct relationship to tasks in the real world where a person requires to reach out and pick up objects and place them in different spatial positions or orientations. Two dimensional input devices do not lend themselves to this task. Even so the majority of CAD tools represent a 3D environment as a series of 3D views. The user has to manipulate objects by referring to one or more of these 2D views. If a large number of objects have to be manipulated then a 2D interaction device is a time consuming device to use. The important characteristic of a 3D environment is the additional dimension - depth. To position an object in 3D space requires a means of manipulating the position and orientation of an object. Devices that can accomplish this task include:
Effective 3D interaction also requires correct visual presentation of the 3D environment. A binocular or stereoscopic display with motion parallex cues is important.
Gestural (Hand and Body)
Gesture represents an important part of human communication and is used to augment other communication forms such as speech. In many ways gesture augmented speech provides a richer form of expression than speech alone. Ever since the glove like devices were available gesture recognition has been claimed to be a useful input modality. Gesture can embody hand and body movements. In essence a gesture is a dynamic pointer and as such makes it important to relate the trend of a gesture into a discrete action. Gestures can be used to signify desired motion or user action. It is even possible to employ the American Sign Language as part of the communication protocol. Gestures are less intuitive than direct manipulation devices and necessitate the user learning a set of unique and distinguishable gestures. Devices that could permit hand gesture recognition include:
Body gesture has also been considered but this depends on being able to incorporate the user's body in the virtual environment. Systems for body gesture recognition have to sense body position and isolate specific body gestures. The ultimate approach is to employ some form of image processing system.
Movement and Navigation in the Virtual Environment
Movement in the virtual environment opens up the possibility of covering great distances without moving in the conventional sense. By using a gestural command it is possible to move through the virtual environment as though you are flying. This has led to the term 'flythrough' being used for this interaction style. Given practice this method can be extremely effective but its usefulness depends upon the application. If the user is required to explore a large architectural structure by this method it is possible to become disorientated because of the lack of kinaesthetic cues. One's sense of spatial awareness is a complex function involving visual perception and motion sensing through feedback from nerve endings in muscles. Gestural input devices are commonly used for indicating movement information..
Speech input has received a variable level of attention over recent years. The development of speech recognition technology is highly advanced and not particularly expensive. The vast majority of systems are speaker dependant which means they have to be trained for each user. This means that each user must store a range of voice templates against which future spoken commands are compared. Early speech input systems were isolated word systems and would only respond to single command utterances. More recent systems employ continuous speech recognition which means they are able to process commands from a sequence of spoken words. Connected speech systems are easier to use since the user can speak in a more natural manner. Under ideal conditions, (low noise environment) recognition accuracies as high as 95% have been achieved. At the moment the need to train the speech recogniser for each user is a barrier which is preventing serious application.
Control of a computer's functionality by eye control has been a practical possibility for many years. The cost of early systems has been prohibitive but the advent of high speed computing and miniature camera systems means that eye control systems are feasible. For people with special needs, eye control of a virtual environment may be extremely effective though more research is required.
There are many visual display technologies that can be used for VR applications. The figure below gives the major types. For educational applications cost will be an important factor. Generally, as you move through non-immersion through to full immersion the cost of the display technology and image generation hardware increases dramatically. For example, a fast desk-top system (non PC based) could cost around £20,000 whereas a fast fully immersive system could range from £120,000-£500,000. Obviously, there is wide variation on these costs but at the lower performance end of the scale the user may find lack of performance interferes with the learning process.
Figure 4 VR Visual Display Technologies
Auditory displays provide an acoustic environment for the user in a virtual environment. Either loudspeakers or headphones could be employed. Localisation refers to the ability to spatialise sound in a 3D environment so that as the user moves their head sound can be perceived as originating from specific point in space. It is not known how important or effective 3D localisation is in enhancing the performance of the user. There are many issues to be resolved covering performance requirements and ambiguous auditory cues.
Haptic/kinaesthetic displays refer to the devices that can communicate a sense of touch and feel to the user. This whole area is extremely complicated and not very well understood. However, it may be crucial for some applications such as medical training where the sense of touch is a very important cue in the training process. There are significant issues to be resolved in this field and current reseach has only just touched the surface (pardon the pun!).
Over recent years there have been many important developments in computing technology that now make it feasible to deliver quite respectible performance for a range of VR applications. Given the range of options and cost it is important to categorise the different performance levels. This means that the overall system architecture needs to be defined in terms of performance and functionality. In an area where cost is important it is necessary to ensure the technology is carefully matched to the task. Over specifing requirements will lead to unacceptably high costs while under specification will lead to unworkable solutions.
Graphics Multimedia Virtual Environments Visualisation Contents