Animation is No Substitute for Virtual Reality

Where does animation end and virtual reality (VR) begin? The extraordinarily realistic animation used in such movies as Jurassic Park and Toy Story isn't VR, no matter how temptingly real the scenes look. Every time you watch Jurassic Park , you're seeing the same set of viewpoints--the ones that Steven Spielberg chose for you. By contrast, virtual reality is a "place" that you can enter, move through, and interact with at will.

What you see in a VR system is not a set of stored images, but rather a view--computed on the fly--onto a database of 3-D object data that describes the geometry and attributes of a virtual world. The VR software ha s to read your current position in virtual space, determine what objects should be visible from this viewpoint, read their coordinates from the database, and transform them into perspective. And, as if that's not hard enough, the software also has to render all the objects in real time--between 10 and 30 times per second, or around 50 milliseconds per frame.

In contrast, an animation is a fixed sequence of prerendered images that were rendered off-line and not in real time. For example, in the making of Toy Story , a network of 117 Sun workstations rendered each frame. Depending on its complexity, a frame could require between 2 and 15 hours to render. Animating the actors' faces took about a week for each 8 seconds of dialogue. Animators are free to use photo-realistic rendering techniques, such as ray tracing and environment mapping, that are not yet feasible for real-time VR systems (except on the most powerful platforms, such as the SGI Onyx/RealityEngine).

For VR systems, rendering speed is paramount to achieve an acceptable refresh rate without flicker. To this end, VR systems often use dynamic schemes that downgrade the level of detail rendered for distant objects or during rapid motion.

Nevertheless, VR and animation technologies have a lot in common, and they will converge more and more as rendering hardware becomes more powerful. You already can use the same 3-D modeling tools, including 3D Studio and TrueSpace, to create objects for use in either VR or animation.