Primitive "virtual reality" systems were first created in the 1990's, since which time humanity has advanced hugely in its ability to recreate the sights and sounds of real environments within an artificial setting. The early VR environments were about as realistic as paper sandwiches, but by about twenty years ago, computers had advanced to the point where VR systems had become common commonplace in the entertainment industry and many government applications. 

The major stumbling block to the virtual reality industry as it existed at this time was physical - however well computer projected images, sounds, other sensory experiences to the user, the virtual space, due to other limitations, was still quite obviously not a real environment. Although body suits capable of simulating tactile impressions had come into use by 2006, they never became an entirely valid substitute for handling physical objects.

What the industry needed was a way to create physical objects in an environment which the user could then interact with. This did not become possible until the discovery of replication technology in 2029; based on refuse-processing nanotechnology and a quirk of quantum physics, the replicator allowed physical objects to be created in a matter of moments and recycled as needed. Unfortunately, realistic holocharacters are a challenge yet to be overcome.

The first commercial grade hologrids were built in in 2036; they used small rooms equipped with a set of holographic projectors which could generate a realistic images of programmed locations onto the walls and ceiling. A replicator would then be employed to create scene-appropriate objects within the room - books in a library, cups in a coffeeshop. Users were finally free of body-harness projection equipment.

Early hologrids suffered from several limitations. Due to the impression of space within the chamber, and no mechanism to restrain a user while appearing to move the space, a careless user could easily walk into a wall. If several users were in one chamber then they could only be as far away from each other as the size of the chamber allowed. The major limitation was, and is, in the creation of characters within the holographic environment; although reasonably realistic images of people and animals can be projected, users can not physically touch these characters in any way. Currently, androids are used as extra characters in certain simulations.

Newer grids have largely overcome the spatial problems; a modern hologrid emits a low-grade disruptive pulse across the floor of the chamber to act as a 'treadmill' effectively keeping the user stationary while the computer moves the replicated objects and adjusts perspective of the holographic projections in relation to the user's movements. Replicated objects reaching the opposite wall are masked until they can be recycled, while images of objects approaching the space within the grid are replicated.

Internal partitioning of the grid, referred to as 'shamming', allows users to appear farther away from each other than they actually are. In modern hologrids, the computer's sensors read the increase in distance from the users' movements on the 'treadmill pulses' and halfway across the holochamber the computer would generate a hologram showing each user an image of the other moving farther away - essentially this process creates two miniature holo-stalls on the grid. When the users head back towards each other the computer holds the 'treadmill pulses' until both users are properly spaced to fit in the chamber, while reversing the images on the divider. A modern hologrid is capable of sub-dividing up to seven times, allowing groups of up to eight people to wander around independently of each other.

The basic mechanism behind the hologrid is GroundLine Industries' Kallisti Projection Diode (KPD). The KPD is a small unit capable of projecting both full colour stereoscopic images and neuro-disruptive pulses. (There are an average of 120,000 per square metre in the average GroundLine HoloSuite.) KPD circuitry is stamped in large sheets, which are then sliced into half-metre square tiles. The average wall of a GroundLine HoloSuite contains twelve sub processing layers, 8mm thick, bonded to lightweight porcelain cooling tiles. The main computer system contains sixteen dedicated processors which power the HoloSuites.

Currently, GroundLine Industries is working on Portable Holographic Imaging (PHI) technology, which would allow holographic guides and translators to reside in a wristwatch sized unit for the convenience of travelling businesspeople.
 
 

Holodeck Specification Sheet based on holochamber specs by Graham Kennedy, 1998.