The ReaCTor

The ReaCTor at UCL is a CAVE-like system where the user stands inside a display that comprises 3 walls and a floor. Usually the ReaCTor is open at the back, but we have built a traversable screen in across the open wall. The traversable screen gives us several opportunities for presenting the ReaCTor in novel ways.

In Milgram and Kishino’s virtuality continuum immersive projection technology (IPT) systems inhabit an extreme point, where the user inhabits a purely virtual environment (VE). An IPT system can completely enclose a user or a small user group in the VE and exclude all interaction with the real environment within which the IPT is situated.

However in our experience it is rarely the case that the IPT actually provides a completely virtual experience. For example it is the nature of many demonstrations, that users enter and leave the IPT whilst the demonstration is in progress, or that conversation takes place between the users inside the IPT and users outside. Indeed, sometimes the IPT is used more like a large screen, with discussions or instructions taking place on the threshold to the IPT. This gives most demonstrations of IPT systems, some elements of a more mixed-reality system, since the real world leaks back into the virtual experience because the IPT does not exclude the real-world.

A two-layer paper screen was placed in front of the ReaCTor completely covering the open fourth side. The paper screen was cut into vertical strips, with the two layers being overlapped so that the light did not normally leak in or out. The two layers prevents the projection from the outside being visible inside, and thus this fourth wall is plain and dark on the inside.

A small projector cast an image on the outside of the screen. The viewpoint for this image was a fixed point at an average eye-level outside the IPT and this was fixed relative to the IPT co-ordinates. This meant that the image appeared to be a window onto the space that followed the IPT user as they navigated the space. An avatar was drawn in the view, so that observers could effectively see the user inside the IPT.

Participants entering or exiting the ReaCTor would pass through the screen and their avatar could appear or disappear at the same time.

We have experimented with using this as a narrative device to explain the ReaCTor system and also to enhance the sense of presence that people have inside the ReaCTor. This is because they are now separated from the spectators and they have traversed from one space to the other.