A positioning system is a system for determining the position of an object in space. Positioning system technologies exist ranging from interplanetary coverage with meter accuracy to workspace and laboratory coverage with sub-millimeter accuracy. A major subclass is made of geopositioning systems, used for determining an object's position with respect to Earth, i.e., its geographical position; one of the most well-known and commonly used geopositioning systems is the Global Positioning System (GPS) and similar global navigation satellite systems (GNSS).
Coverage
Interplanetary systems Interplanetary-radio communication systems not only communicate with spacecraft, but they are also used to determine their position. Radar can track targets near the Earth, but spacecraft in deep space must have a working transponder on board to echo a radio signal back. Orientation information can be obtained using star trackers.
Global systems
Global navigation satellite systems (GNSS) allow specialized radio receivers to determine their 3-D space position, as well as time, with an accuracy of 2–20 metres or tens of nanoseconds. Currently deployed systems use microwave signals that can only be received reliably outdoors and that cover most of Earth's surface, as well as near-Earth space. The existing and planned systems are:
Global Positioning System – US military system, fully operational since 1995 GLONASS – Russian military system, fully operational since October 2011 Galileo – European Community, fully operational since December 2019 Beidou navigation system – China, fully operational since June 2020 Indian Regional Navigation Satellite System – a planned project in India
Regional systems Networks of land-based positioning transmitters allow specialized radio receivers to determine their 2-D position on the surface of the Earth. They are generally less accurate than GNSS because their signals are not entirely restricted to line-of-sight propagation, and they have only regional coverage. However, they remain useful for special purposes and as a backup where their signals are more reliably received, including underground and indoors, and receivers can be built that consume very low battery power. LORAN is an example of such a system.
Local systems A local positioning system (LPS) is a navigation system that provides location information in all weather, anywhere within the coverage of the network, where there is an unobstructed line of sight to three or more signaling beacons of which the exact position on Earth is known. Unlike GPS or other global navigation satellite systems, local positioning systems don't provide global coverage. Instead, they use beacons, which have a limited range, hence requiring the user to be near these. Beacons include cellular base stations, Wi-Fi and LiFi access points, and radio broadcast towers. In the past, long-range LPS's have been used for navigation of ships and aircraft. Examples are the Decca Navigator System and LORAN. Nowadays, local positioning systems are often used as complementary (and in some cases alternative) positioning technology to GPS, especially in areas where GPS does not reach or is weak, for example, inside buildings, or urban canyons. Local positioning using cellular and broadcast towers can be used on cell phones that do not have a GPS receiver. Even if the phone has a GPS receiver, battery life will be extended if cell tower location accuracy is sufficient. They are also used in trackless amusement rides like Pooh's Hunny Hunt and Mystic Manor. Examples of existing systems include
Locata Corporation Pseudolite
Indoor systems
Indoor positioning systems are optimized for use within individual rooms, buildings, or construction sites. They typically offer centimeter-accuracy. Some provide 6-D location and orientation information. Examples of existing systems include
Active Bat
Workspace systems These are designed to cover only a restricted workspace, typically a few cubic meters, but can offer accuracy in the millimeter-range or better. They typically provide 6-D position and orientation. Example applications include virtual reality environments, alignment tools for computer-assisted surgery or radiology, and cinematography (motion capture, match moving). Examples: Wii Remote with Sensor Bar, Polhemus Tracker, Precision Motion Tracking Solutions InterSense.
High performance High performance positioning system is used in manufacturing processes to move an object (tool or part) smoothly and accurately in six degrees of freedom, along a desired path, at a desired orientation, with high acceleration, high deceleration, high velocity and low settling time. It is designed to quickly stop its motion and accurately place the moving object at its desired final position and orientation with minimal jittering. Examples: high velocity machine tools, laser scanning, wire bonding, printed circuit board inspection, lab automation assaying, flight simulators
Technologies Multiple technologies exist to determine the position and orientation of an object or person in a room, building or in the world.
Acoustic positioning
Time of flight Time of flight systems determine the distance by measuring the time of propagation of pulsed signals between a transmitter and receiver. When distances of at least three locations are known, a fourth position can be determined using trilateration. Global Positioning System is an example. Optical trackers, such as laser ranging trackers suffer from line of sight problems and their performance is adversely affected by ambient light and infrared radiation. On the other hand, they do not suffer from distortion effects in the presence of metals and can have high update rates because of the speed of light. Ultrasonic trackers have a more limited range because of the loss of energy with the distance traveled. They are also sensitive to ultrasonic ambient noise and have a low update rate. However, they have an advantage that they do not need line of sight. Systems using radio waves such as the Global navigation satellite system do not suffer ambient light, but still need line of sight.
Spatial scan A spatial scan system uses (optical) beacons and sensors. Two categories can be distinguished:
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