A positioning system is a mechanism for determining the location of an object in space. Technologies for this task exist ranging from worldwide coverage with meter accuracy to workspace coverage with sub-millimetre accuracy.
Interplanetary-radio communication system not only communicate with spacecraft, but are also used to determine their position. This can be done either using a transponder on board a spacecraft that echoes a radio signal back, or using radar. Orientation information can be obtained using star trackers.
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 – On 21 October 2011 the first two of four operational satellites were launched the next two will follow in 2012. Expected completion is 2019
- Beidou navigation system – a planned project in China
- Indian Regional Navigation Satellite System – a planned project in India
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 such a system.
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
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.