Positioning technologies
Encyclopedia
Positioning systems
will use positioning technology to determine the position and orientation of an object or person in a room, building or in the world.
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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.
By aiming the sensor at the beacon the angle between them can be measured. With triangulation
the position of the object can be determined.
is that it does not require an external reference. Instead it measures rotation with a gyroscope
or position with an accelerometer
with respect to a known starting position and orientation. Because these systems measure relative positions instead of absolute positions it can suffer from accumulated errors end therefore is subject to drift. A periodic re-calibration of the system will provide more accuracy.
Like inertial sensing systems, phase-difference systems can suffer from accumulated errors end therefore is subject to drift, but because the phase can be measured continuesly they are able to generate high data rates.
uses the earth magnetic field to know its orientation in two directions. An inclinometer
uses the earth gravitational field
to know its orientation in the remaining third direction.
The field used for positioning do not need to origin from nature. According to Ampère's law
a magnetic field is generated in a coil when an electric current circulates this coil. To measure position and orientation of a receiver in space, the emitter must be composed of three coils placed perpendicular to each other, thus defining a spatial referential from which a magnetic field can exit in any direction. The direction is given by the resultant of three elementary orthogonal directions. On the receiver, three sensors measure the components of the field’s flux received as a consequence of magnetic coupling. Based on these measures, the system determines the position and orientation of the receiver with respect to the emitter attached to the reference.
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Positioning system
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 systems :...
will use positioning technology to determine the position and orientation of an object or person in a room, building or in the world.
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 trilaterationTrilateration
In geometry, trilateration is the process of determinating absolute or relative locations of points by measurement of distances, using the geometry of circles, spheres or triangles. In addition to its interest as a geometric problem, trilateration does have practical applications in surveying and...
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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
Ultrasonic sensor
Ultrasonic sensors work on a principle similar to radar or sonar which evaluate attributes of a target by interpreting the echoes from radio or sound waves respectively. Ultrasonic sensors generate high frequency sound waves and evaluate the echo which is received back by the sensor...
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
Radio waves
Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies from 300 GHz to as low as 3 kHz, and corresponding wavelengths from 1 millimeter to 100 kilometers. Like all other electromagnetic waves,...
such as the Global navigation satellite system
Global Navigation Satellite System
A satellite navigation or SAT NAV system is a system of satellites that provide autonomous geo-spatial positioning with global coverage. It allows small electronic receivers to determine their location to within a few metres using time signals transmitted along a line-of-sight by radio from...
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:- Inside out systems where the beacon is placed at a fixed position in the environment and the sensor is on the object
- Outside in systems where the beacons are on the target and the senors are at a fixed position in the environment
By aiming the sensor at the beacon the angle between them can be measured. With triangulation
Triangulation
In trigonometry and geometry, triangulation is the process of determining the location of a point by measuring angles to it from known points at either end of a fixed baseline, rather than measuring distances to the point directly...
the position of the object can be determined.
Inertial sensing
The main advantage of an inertial sensingInertial navigation system
An inertial navigation system is a navigation aid that uses a computer, motion sensors and rotation sensors to continuously calculate via dead reckoning the position, orientation, and velocity of a moving object without the need for external references...
is that it does not require an external reference. Instead it measures rotation with a gyroscope
Gyroscope
A gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum. In essence, a mechanical gyroscope is a spinning wheel or disk whose axle is free to take any orientation...
or position with an accelerometer
Accelerometer
An accelerometer is a device that measures proper acceleration, also called the four-acceleration. This is not necessarily the same as the coordinate acceleration , but is rather the type of acceleration associated with the phenomenon of weight experienced by a test mass that resides in the frame...
with respect to a known starting position and orientation. Because these systems measure relative positions instead of absolute positions it can suffer from accumulated errors end therefore is subject to drift. A periodic re-calibration of the system will provide more accuracy.
Mechanical linkage
This type of tracking system uses mechanical linkages between the reference and the target. Two types of linkages have been used. One is an assembly of mechanical parts that can each rotate providing the user with multiple rotation capabilities. The orientation of the linkages is computed from the various linkages angles measured with incremental encoders or potentiometers. Other types of mechanical linkages are wires that are rolled on coils. A spring system ensures that the wires are tensed in order to measure the distance accurately. The degrees of freedom sensed by mechanical linkage trackers are dependent upon the constitution of the tracker mechanical structure. While six degrees of freedom are most often provided, typically only a limited range of motions is possible because of the kinematics of the joints and the length of each link. Also, the weight and the deformation of the structure increase with the distance of the target from the reference and impose a limit on the working volume.Phase difference
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 calculatedLike inertial sensing systems, phase-difference systems can suffer from accumulated errors end therefore is subject to drift, but because the phase can be measured continuesly they are able to generate high data rates.
Direct field sensing
Direct field sensing systems use a known field to derive orientation or position: A simple compassCompass
A compass is a navigational instrument that shows directions in a frame of reference that is stationary relative to the surface of the earth. The frame of reference defines the four cardinal directions – north, south, east, and west. Intermediate directions are also defined...
uses the earth magnetic field to know its orientation in two directions. An inclinometer
Inclinometer
An inclinometer or clinometer is an instrument for measuring angles of slope , elevation or depression of an object with respect to gravity...
uses the earth gravitational field
Earth's gravity
The gravity of Earth, denoted g, refers to the acceleration that the Earth imparts to objects on or near its surface. In SI units this acceleration is measured in metres per second per second or equivalently in newtons per kilogram...
to know its orientation in the remaining third direction.
The field used for positioning do not need to origin from nature. According to Ampère's law
Ampère's law
In classical electromagnetism, Ampère's circuital law, discovered by André-Marie Ampère in 1826, relates the integrated magnetic field around a closed loop to the electric current passing through the loop...
a magnetic field is generated in a coil when an electric current circulates this coil. To measure position and orientation of a receiver in space, the emitter must be composed of three coils placed perpendicular to each other, thus defining a spatial referential from which a magnetic field can exit in any direction. The direction is given by the resultant of three elementary orthogonal directions. On the receiver, three sensors measure the components of the field’s flux received as a consequence of magnetic coupling. Based on these measures, the system determines the position and orientation of the receiver with respect to the emitter attached to the reference.
Hybrid systems
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 with a system with absolute position measurement. Systems combing two or more technologies are called hybrid positioning systemsHybrid positioning system
Hybrid positioning systems are systems for finding the location of a mobile device using several different positioning technologies. Usually GPS is one major component of such systems, combined with cell tower signals, wireless internet signals, Bluetooth sensors or other local Positioning...
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See also
- Positioning systemPositioning systemA 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 systems :...
- Virtual realityVirtual realityVirtual reality , also known as virtuality, is a term that applies to computer-simulated environments that can simulate physical presence in places in the real world, as well as in imaginary worlds...
- Eye trackingEye trackingEye tracking is the process of measuring either the point of gaze or the motion of an eye relative to the head. An eye tracker is a device for measuring eye positions and eye movement. Eye trackers are used in research on the visual system, in psychology, in cognitive linguistics and in product...
- Handheld trackerHandheld trackerA handheld tracker uses a variety of technologies including GPS , GSM and GPRS to enable companies and parents to track and communicate with their workers and children and elderly parents...
- Real-time locating systemReal-time locating systemReal-time locating systems are a type of local positioning system that allow to track and identify the location of objects in real time. Using simple, inexpensive badges or tags attached to the objects, readers receive wireless signals from these tags to determine their locations...