Positioning system

Technology for determining an object's location in space

A positioning system is a system for determining the position of an object in space. One of the most well known and commonly used positioning systems is the Global Positioning System (GPS). Positioning system technologies exist ranging from worldwide coverage with meter accuracy to workspace coverage with sub millimeter accuracy.

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.

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.

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.

Multiple technologies exist to determine the position and orientation of an object or person in a room, building or in the world.

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. Also they are sensitive to ultrasonic ambient noise and have a low update rate. But the main advantage is 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.

Phase difference systems measure the shift in phase of an incoming signal from an emitter on a moving target compared to the phase of an incoming signal from a reference emitter. With this the relative motion of the emitter with respect to the receiver can be calculated. Like inertial sensing systems, phase difference systems can suffer from accumulated errors and therefore are subject to drift, but because the phase can be measured continuously they are able to generate high data rates. Omega (navigation system) is an example.

Direct field sensing systems use a known field to derive orientation or position: A simple compass uses the Earth's magnetic field to know its orientation in two directions.

Because every technology has its pros and cons, most systems use more than one technology. A system based on relative position changes like the inertial system needs periodic calibration against a system with absolute position measurement. Systems combining two or more technologies are called hybrid positioning systems. Hybrid positioning systems are systems for finding the location of a mobile device using several different positioning technologies. Usually GPS (Global Positioning System) is one major component of such systems, combined with cell tower signals, wireless internet signals, Bluetooth sensors, IP addresses and network environment data. These systems are specifically designed to overcome the limitations of GPS, which is very exact in open areas, but works poorly indoors or between tall buildings (the urban canyon effect). By comparison, cell tower signals are not hindered by buildings or bad weather, but usually provide less precise positioning. Wi Fi positioning systems may give very exact positioning, in urban areas with high Wi Fi density and depend on a comprehensive database of Wi Fi access points. Hybrid positioning systems are increasingly being explored for certain civilian and commercial location based services and location based media, which need to work well in urban areas in order to be commercially and practically viable. Early works in this area include the Place Lab project, which started in 2003 and went inactive in 2006. Later methods let smartphones combine the accuracy of GPS with the low power consumption of cell ID transition point finding. In 2022, the satellite free positioning system SuperGPS with higher resolution than GPS using existing telecommunications networks was demonstrated.