that generates or synthesizes virtual worlds with which the operator can interact. Whereas the purpose of a teleoperator system is to sense and transform the real world (as in removal of hazardous waste by teleoperation), the purpose of a virtual environment system is to alter the state of the human operator or the computer (as in the use of virtual environment systems for training, designing, marketing, or scientific modeling). In many systems, such as teleoperator systems that make use of virtual environment systems to help plan future actions, teleoperator systems and virtual environment systems are combined. In an augmented-reality system, the operator's interaction with the real world (either directly or via a teleoperator system) is enhanced by overlaying the associated real-world information with information stored in the computer (generated from models, derived previously from other sensing systems, etc.). In general, we refer to all systems of the types just described as synthetic environment (SE) systems.

Virtual environment systems differ from traditional simulator systems in that they rely much less on physical mock-ups for simulating objects within reach of the operator and are much more flexible and reconfigurable. Virtual environment systems differ from other previously developed computer-centered systems in the extent to which real-time interaction is facilitated, the perceived visual space is three-dimensional rather than two-dimensional, the human-machine interface is multimodal, and the operator is immersed in the computer-generated environment.

In recent years, synthetic environment systems, particularly virtual environment systems, have generated both great excitement and great confusion. These factors are evident in the extensive material published in the popular press; in the unrealistic expectations on the part of the public; in the inadequate terminology being used; in the deluge of conferences, articles, books, and demonstrations occurring; in the difficulties being experienced in communicating across disciplinary boundaries even by individuals whose professional work lies within the domain of synthetic environment systems; and in the frenetic pace at which most of the individuals concerned with synthetic environments are working.

In this book, we attempt to describe the current state of research and technology that is relevant to the development of synthetic environment systems, provide a summary of the application domains in which such systems are likely to make major contributions, and outline a series of recommendations that we believe are crucial to rational and systematic development of the synthetic environment field. Inasmuch as the ''bottom line" of the committee's work is our recommendations (presented in the final section of the overview), the remainder of this executive summary focuses on these recommendations. They are summarized under

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