Global Positioning System Reference
In-Depth Information
from the construction industry if building panels were made with tags already
embedded or from consumer gaming, taking the approach pioneered in the
Nintendo Wii further, with highly accurate indoor 3D positioning and body-
wearable ultrasonic sensors. For all its problems, ultrasonics still offers a very
good trade-off in terms of accuracy and cheapness.
7.3.3
The Massachusetts Institute of Technology (MIT) Crickets
MIT [3] researched a similar system to the Bats but that worked in a reverse
mode. The “cricket” modules were attached to the ceilings of rooms and
transmitted ultrasonic pulses. Mobile receivers were carried by people and
attached to objects. Before the ultrasonic pulse is transmitted each ceiling cricket
transmits a radio signal modulated with identity information. The time difference
between the RF and ultrasonic signals is timed and a ranging measurement made.
The measurements are repeated by the cricket receiver for a number of
transmitters so that triangulation can determine exact position.
The main difference is that this is an autonomous system and unlike the Bat
system would not have a specific upper limit on uses that could be supported. A
further enhancement (as with the Bat system) is that orientation is possible if more
than one receiver is used when attached to an object being positioned. Other
sensors may also be incorporated.
7.4
Visual Positioning
7.4.1
Outside-In Positioning
Machine vision is a very effective and emerging technology for finding the 3D
position of a target that can be seen or can see. Visual positioning is the primary
method that our species uses, and as artificial intelligence and machine-learning
techniques advance and become cheaper, the technique is likely to increase. There
is an associated reason to use camera technology for positioning: the need for
increased security in a more uncertain world. If cameras are needed to enforce and
deter crime, then it may be a bonus to be able to enhance the system. First, to
recognize targets within a scene; second, to track their motion; and finally, to
present the information in a useful and automatic way to those who need it. There
are already many users of this technology that include national security systems,
computer gaming, and many applications that are relevant to ITS. All the
applications where a fixed camera looks into a scene are known as outside-in
systems.
