Applications
Starfleet personnel use holodecks for training, diagnostics and recreation. Holodecks are used to recreate or simulate settings and events for analysis, such as to explore the forensics and logistics of a crime scene for law enforcement purposes, or for scientific experimentation. In general, the holodeck "functions as a cultural repository of narrative possibilities that would normally be excluded from the ship's own sociohistorical moment" and "allows the Enterprise community to include even that which it excludes by containing the excluded within a proper, controlled place which in no way intrudes upon the everyday space of the ship."
The Emergency Medical Hologram on ships such as USS Voyager applies holodeck technology to present a single "character" within the otherwise natural environment of the ship's sick bay.
An example of the holodeck's recreational functions are the holosuites that are owned and rented out – often for sexual purposes – by Quark on Deep Space Nine.
Writing stories and plotlines for the holodeck is an activity pursued by people known as holonovelists. It was the chosen profession of Lt. Tom Paris of the USS Voyager, and he pursued it when the ship finally returned from the Delta Quadrant in the show's finale.
The Holosuites and holodecks utilize two major subsystems: the holographic image and the conversion of matter. The holographic imaging system creates realistic environments and landscapes. The conversion system of matter creates physical objects from the central supply of raw materials from the ship. Under normal conditions, a participant in a holographic simulation should not be able to distinguish a real object from a simulated one.
The holodeck also generates impressive recreations of humanoid and other forms of life by means of precisely-shaped force fields covered by holographic imagery, with the effect that they seem solid to the touch. They are made to move by use of tractor beams, resulting in highly articulated and computer-controlled "puppets" which are exceptionally realistic, showing nearly equal behavior to that exhibited by living beings, depending, of course, on the limits of the software involved. However, the replication-based material transport system is obviously unable to reproduce a living being.
Solid, inanimate objects on the holodeck—items such as a book, a rock, or an apple—are composed of matter arranged by the replication system and, when deemed appropriate by the computer system, can be interacted with or even consumed. Objects created by replication of matter are physically real and can indeed be removed from the holodeck, noting only that they will no longer be under the control of the computer once removed from the simulation. However, objects created on the holodeck that are purely images can not be removed from the simulated environment, even if they seem to have a physical reality due to the force fields. In order for a given item to be removed from the environment of the holodeck, a person would need to be holding the object as he/she leaves.
The basic mechanism behind the holodeck is the omnidirectional holo-diode (HDO or OHD, its acronym in English). The HDO comprises two types of micro-miniature devices that project a variety of special force field. The density of HDOS in a holographic surface is 400 per square centimeter, fed by an outlet electroplasma medium power. Entire walls are covered with HDOS, manufactured in an inexpensive process of printing circuits on a roll.
A typical surface holodeck includes twelve sub-layers processed a total of 3.5 mm, fused to a thermal-structural light panel, which on average is 3.04 cm thick. The primary materials include sub-processor/emitter of superconducting material. Each individual HDO measures 0.01 mm. The mechanism of digital optical network, by which an HDOS receive impulses, is similar to that which feeds smaller display panels, although the walls are divided into major sections, and easier to control with greater speed, each with 0.61 m². Sub-sections which are dedicated to the main computer can control such "monitors" which are the size of rooms.
Besides the ability to project stereoscopic color images, HDOS manipulate the force fields in three dimensions to allow visitors to "feel" objects that are not really there. This tactile stimulus provides the appropriate response one would expect from a rock on the ground or a tree growing in a forest. The only factors limiting the number and types of object are given by the computer memory and time to retrieve or calculate the beginning pattern of an object, either real or imaginary.
The version of "optics" of a HDO sends a complete picture of the environment or landscape, based on their location relative to the full panel. The visitor, however, sees only a small portion of each HDOS, almost like a fly's eye operating in reverse. When the visitor moves the visible portions of HDOS change, changing the perspective. In reality, the energy emitted is not a visible electromagnetic emission, but is actually polarized patterns of interference. The image is reconstructed where the patterns intersect the lens of the eye or any visual receiver.
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