A binocular head-mounted display
(HMD).
A
head-mounted display or
Helmet mounted display, both
abbreviated 'HMD', is a display device, worn on the head or as part
of a helmet, that has a small display optic in front of one
(monocular HMD) or each eye (binocular HMD).
Overview
A typical HMD has either one or two small displays with lenses and
semi-transparent mirrors embedded in a helmet, eye-glasses or
visor. The display units are miniaturised and may include
CRT,
LCDs,
Liquid crystal on silicon (LCos),
or
OLED. Some vendors
employ multiple micro-displays to increase total resolution and
field of view.
Types
HMDs differ in whether they can display just a
computer generated image (CGI),
show live images from the real world or a combination of both.
- Most HMDs display only a computer-generated image, sometimes
referred to as a virtual image
- Some HMDs allow superimposing a CGI upon a real-world view.
This is sometimes referred to as augmented reality or mixed reality.
Combining real-world view with CGI can be done by projecting the
CGI through a partially reflective mirror and viewing the real
world directly. This method is often called Optical See-Through.
Combining real-world view with CGI can also be done electronically
by accepting video from a camera and mixing it electronically with
CGI. This method is often called Video See-Through.
Applications
Major HMD applications include military, governmental (fire,
police, etc.) and civilian/commercial (medicine, video gaming,
sports, etc.).
Aviation
Ruggedized HMDs are increasingly being integrated into the
cockpits of modern helicopters and fighter aircraft.
These are usually fully integrated with the pilot's flying helmet
and may include protective visors,
night vision devices and displays of
other symbology.
Tactical / ground
Military, police and firefighters use HMDs to display tactical
information such as maps or thermal imaging data while viewing the
real scene. Recent applications have included the use of HMD for
paratroopers .
In 2005, the Liteye HMD was introduced for ground combat troops as
a rugged, waterproof lightweight display that clips into a standard
US PVS-14 military helmet mount. The self-contained color monocular
OLED display replaces
the NVG tube and connects to a mobile computing device. The LE has
see-through capability and can be used as a standard HMD or for
augmented reality applications.
The design is optimized to provide high definition data under all
lighting conditions, in covered or see-through modes of operation.
The LE has a low power consumption, operating on four AA batteries
for 35 hours or receiving power via standard
USB connection. .
Engineering, science and medicine
Engineers and scientists use HMDs to provide stereoscopic views of
CAD schematics. These systems
are also used in the maintenance of complex systems, as they can
give a technician what is effectively "x-ray vision" by combining
computer graphics such as system diagrams and imagery with the
technician's natural vision. There are also applications in
surgery, wherein a combination of radiographic data (
CAT scan and
MRI imaging) is combined with the
surgeon's natural view of the operation.
Gaming
Disney HMD mount
Low cost HMD devices are available for use with 3D games and
entertainment applications.
One of the pioneers in this field was Sony who released the
Glasstron in 1997, which had as an optional accessory a positional
sensor which permitted the user to view the surroundings, with the
perspective moving as the head moved, providing a deep sense of
immersion.
One novel application of this technology was in the game
Mechwarrior 2, which permitted users of the sony glasstron to adopt
a new visual perspective from inside the cockpit of the craft,
using their own eyes as visual and seeing the battlefield through
their craft's own cockpit.
Sports
A HMD system has been developed for
Formula
One drivers by Kopin Corp. and the
BMW
Group. According to BMW, “The HMD is part of an advanced telemetry
system approved for installation by the Formula One racing
committee… to communicate to the driver wirelessly from the heart
of the race pit.”
The HMD will display race crew critical race data while allowing
the driver to continuing to focus on the track. Pit crews control
the data and messages sent to their drivers through two-way
radio.
Performance parameters
- Stereoscopic imagery. A binocular HMD has the potential to
display a different image to each eye. This can be used to show
stereoscopic images. It should be heeded
that so-called 'Optical Infinity' is generally taken by flight
surgeons and display experts as about 9 metres. This is the
distance at which, with the average human eye rangefinder
"baseline" (distance between the eyes or Inter-Pupillary Distance (IPD)) of
between 2.5 and 3 inches (6 and 8 cm), the angle of an object at
that distance, becomes essentially the same from each eye. At
smaller ranges the perspective from each eye is significantly
different and the expense of generating two different visual
channels through the Computer-Generated Imagery (CGI) system,
becomes worthwhile.
- Field of view (FOV) – Humans have
around 180° FOV, but most HMDs offer considerably less than this.
Typically, greater field of view results in greater sense of
immersion and better situational awareness. Most people do not have
a good feel for what a particular quoted FOV would look like (e.g.
25°) so often manufacturers will quote an apparent screen size.
Most people sit about 60 cm away from their monitors and have quite
a good feel about screen sizes at that distance. To convert the
manufacturer's apparent screen size to a desktop monitor position,
just divide the screen size by the distance in feet, then multiply
by 2.
- Resolution – HMDs usually mention either the total number of
pixels or the number of pixels per degree. Listing the total number
of pixels (e.g. 1600×1200 pixels per eye) is borrowed from how the
specifications of computer monitors are presented. However, the
pixel density, usually specified in pixels per degree or in
arcminutes per pixel, is also used to determine visual acuity. 60
pixels/° (1 arcmin/pixel) is usually referred to as eye limiting
resolution, above which increased resolution is not noticed by
people with normal vision. HMDs typically offer 10 to 20 pixels/°,
though advances in micro-displays help increase this number.
- Binocular overlap - measures the area that is common to both
eyes. Binocular overlap is the basis for the sense of depth and
stereo, allowing humans to sense which objects are near and which
objects are far. Humans have a binocular overlap of about 100° (50°
to the left of the nose and 50° to the right). The larger the
binocular overlap offered by an HMD, the greater the sense of
stereo. Overlap is sometimes specified in degrees (e.g. 74°) or in
percent indicating how much of the visual field of each eye is
common to the other eye.
- Distant focus ('Collimation'). Optical techniques may be used
to present the images at a distant focus, which seems to improve
the realism of images that in the real world would be at a
distance.
- Inter-Pupillary Distance
(IPD). This is the distance between the two eyes, measured at the
pupils, and is important in designing Head-Mounted Displays.
Peripherals
- The most rudimentary HMDs simply project an image or symbology
on a wearer’s visor or reticle. The image is not slaved to the real
world (i.e., the image does not change based on the wearer’s head
position).
- More sophisticated HMDs incorporate a positioning system that tracks the
wearer’s head position and angle, so that the picture or symbology
displayed is congruent with the outside world using see-through
imagery.
- Head tracking – Slaving the imagery. Head-mounted displays may
also be used with tracking sensors that allow changes of angle and
orientation to be recorded. When such data is available in the
system computer, it can be used to generate the appropriate
computer-generated imagery (CGI) for the angle-of-look at the
particular time. This allows the user to "look around" a virtual reality environment simply by moving
the head without the need for a separate controller to change the
angle of the imagery. In radio-based systems (compared to wires),
the wearer may move about within the tracking limits of the
system.
- Eye tracking – Eye trackers measure the point of gaze, allowing
a computer to sense where the user is looking. This information is
useful in a variety of contexts such as user interface navigation :
by sensing the user's gaze, a computer can change the information
displayed on a screen, bring additional details into attention,
etc.
HMD manufacturers (alphabetically)
Companies that have produced HMDs include:
Human measurements
The 95 percentile adult male in the USA has an IPD of 70 mm (2.8
in) and the 5 percentile, 58 mm (2.3 in). For adult females in the
USA the figures are 65 and 53 mm (2.6 and 2.1 in). For Europeans
the figures are 1 mm smaller.
- Anthropometry. The IPD is one of the many
measurements used in anthropometry, measurements of the human body.
The statistical spread of these measurements, usually expressed as
percentiles, is used for many purposes such as designing the size
of airline seating and clothing sizes. In the case of IPD, it is
used in specifying the size range not only for Head-Mounted Display
systems but also for eyeglasses (spectacles), binoculars and other
optics.
See also
Commercial products
- Headplay, a high resolution commercial
HMD, capable of stereoscopy
- Virtual Boy, a video game platform
with an HMD
- Sensics a commercial HMD with panoramic
field of view and high resolution
- Shimadzu Data Glass 3/A, a 800x600 resolution
commercial HMD
- Oculon OLED 800×600 resolution HMD
- Glasstron The Sony Glasstron was a
portable head-mounted display
- Myvu Award-winning eyewear for video up
close & personal
- Cinemavision, MRI compatible
patient audio and video system
- Vu Technologies Luxury in
Technology
References
- A Three Dimensional Helmet Mounted Primary Flight
Reference for Paratroopers
- www.defense-update.com/.../l/liteye-displays.htm
- http://www.sid.org/news/archive/industrynews0210.html
External links
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