Global Positioning System Reference
In-Depth Information
receivers is required. Some experiments have taken place where active badges
communicate with each other, leading to the idea of passing location information
in a viral manner. Other proposals have been to deploy IR lighthouses where a
rotating beam provides angle information (for example, to sectorize a room), but
active IR badges have yet to make a major impact on Whereness.
7.2.2
IR Gaming Positioning
The Nintendo Wii games machine uses IR positioning and is currently one of the
most popular consumer electronic devices with demand far outstripping sales. A
sensor bar is placed horizontally in front of the TV screen with two short rows of
LEDs at each end. The handheld games controller contains an IR camera on its
end that is pointed in the general direction of the sensor bar. The image of the
LEDs is used by the games software to detect the approximate location of each
player's controller and is used as an input in various sports simulation games
(which are the unique feature of the Wii).
7.2.3
IR Ranging and LIDAR
IR ranging is used in some autofocus cameras using a triangulation or a pulse
timing approach but much more accurate ranging is used professionaly in light
detection and ranging (LIDAR), which is used in surveying, geodesy, and other
scientific activities where accurate distances need to be determined. High-power
laser light is used and the longer wave part IR spectrum has the advantage of
being eye-safe. Very accurate 3D spatial images can be determined automatically
by scanning with rotating beams (using mirrors), and ground terrain models can
be made by aerial lidar survey. It is likely that as technology costs fall, advanced
techniques such as lidar may enter consumer products and mainstream business,
adding a new dimension to photography, art, gaming, amateur mapping, and the
surveillance of important physical assets.
7.3
Sonic and Ultrasonic Positioning
Ultrasound is sound that is above the limit of human hearing, which is around 25
kHz for young people and can be used for positioning and imaging. Sound is the
longitudinal physical pressure vibrations of matter and travels much more slowly
than electromagnetic radiation. In air the propagation speed is around 340m per
second (i.e., around a million times slower than light speed) but is an order of
magnitude faster in solids. Sonic positioning is used in maritime sound,
navigation, and ranging systems (sonar), for applications including finding shoals
of fish, the depth of the sea bed, remote vessels, and military targets. On land, the
nuisance of loud audible pulses rules out sonar in favor of ultrasonics. The higher
