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screen they are sent.There are three classes currently in use. Monocular HMD's present a
single image to one eye, biocular ones deliver a single image to both eyes, and binocular
HMD's display different images to each eye. Only the last class of HMD can be used for
the presentation of truly stereoscopic image.
Head-mounted displays generally project virtual images. Specifically, a see-through (or
augmented vision) helmet mounted display presents a virtual image which is perceived as
being in the same place as a background scene.Viewing a real image requires an image
plane or viewing screen and defeats the purpose of the transparent display.The funda-
mental difference between a real and a virtual image is that a real image can be viewed at
an accessible plane in space, with a screen of some sort, while a virtual image can not.
Current limitations which have been recognised and should be overcome in the near
future are:
- inadequate display update rates;
- equipment weight leading to user discomfort;
- inability to provide high resolution with a broad field of view.
Liquid Crystal Shutterglasses
Shutterglasses are glasses which transform the way the user sees the image on a standard
monitor.They are used together with a normal CRT monitor, but normally not with
LCD ones.The two images required for stereoscopic vision are displayed on the standard
monitor in turns.The image for the left eye is displayed for some fraction of a second,
after that the image for the right eye appears for the same duration of time and so on.The
job of the glasses is to prevent the left eye from seeing the image dedicated to the right
eye and vice versa.To achieve the illusion of 3D imaging from a standard display the shut-
ters on the glasses open and close at a rate faster than the user is able to perceive.
Applications in Augmented Reality
Displays that interactively blend 3D virtual objects with the real world around the user
have tremendous potential to help real-world tasks in navigation, the maintenance and
assembly of complex equipment, medical visualisation, and entertainment. For example,
in the future a motorist wearing a pair of `magic glasses' might look under the bonnet of
her car and see 3D animations and directions superimposed on her engine to guide her
in repairing the system.
Applications in Human Tracking
While computers today are good at producing large output bandwidth, input band-
width on the user's actions is usually extremely limited: keyboard clicks, mouse move-
ments, and occasionally speech. Accurate tracking of the user's position and orientation is
an enabling technology for more sophisticated future human-computer interfaces.These
trackers will have to be accurate, long range, minimally encumbering, and have to work
in many different environments, including weather-susceptible locations. Hybrid combi-
nations of different technologies will be key in this respect.
Applications in Virtual Environments
Immersive systems using head-mounted displays and large head-tracked stereo display,
offer a more natural and intuitive interface for certain applications, including training,
simulation, and prototyping.
Human Interfaces
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