This book, Developing Virtual Reality Applications: Foundations of Effective Design, has been many years in the making. Our interest in virtual reality came about as an outgrowth of our interest in, and our day-to-day work in scientific visualization. In the early 1990s the state-of-the-art in computer graphics used for scientific visualization was to take scientific data, clean it up, create geometry from it, place computer graphics lights, choose a camera perspective, and then render, not in real time, single images of computer graphics output. To create animations, one then created a sequence of images where either the camera perspective, or the underlying data evolves over time. The resulting images could be recorded to video tape or film, and played back as an animation.
There are several obvious drawbacks in that scenario. A fairly typical rendering time was about 20 minutes per frame. As technology improved, and rendering rates increased, frames still typically took about 20 minutes to render, because designers chose to render frames of greater complexity. Thus, scientific visualization animations were primarily used as an explanatory tool, rather than as an interactive, exploratory, real-time mechanism for exploring data. The use of computer graphics in other areas, such as Computer Aided Design, animated movies, architecture, and others followed a similar course of development.
The obvious thing that was missing was the human in the loop. The improvement in computer hardware and software allowed pseudo real-time computer graphics to be produced. This allowed new imagery to be generated as time evolved in the underlying data and/or the viewer changed their physical perspective to see the imagery from a different point of view.