3D tracking system

Position and orientation tracking using laser interferometers

Polhemus 3Draw 3D pen digitizer

WorldSense positional tracking, an example of camera-based tracking

3D tracking is the process of measuring an object's position and orientation in three-dimensional space, playing a crucial role in spatial computing. 3D tracking is used for head tracking and hand tracking.

Types of spatial tracking systems include infra-red, electromagnetic, and acoustic.

3D tracking can be categorized into the following types:

• 3DOF position tracking: Determines the location of an object along three spatial axes (X, Y, Z).
• 3DOF rotation tracking: Measures an object's rotation around three axes
• 6DOF tracking: Combines both position and rotation tracking, providing a full representation of an object's pose in space.

A system constitutes an absolute positioning system.

Systems

Spatial tracking systems track two separate variables: The position of something, and the rotation of the same thing, which is also known as orientation. Some tracking systems use the same physical principle to track both, but other systems are more effective by using one method to track position and another to track rotation.

For example, a hybrid system may track position using multilateration and tracks rotation using a magnetic sensor.

Some types of 3D tracking are more suitable for head tracking, and some are more suitable for hand tracking or handheld pen tracking. Electromagnetic tracking is an example of a type that is suitable for head tracking. Acoustic 3D tracking is an example of a type that is suitable for hand tracking. Acoustic tracking is not suitable for head tracking because loud sounds can interrupt it, causing the display to not be updated correctly, causing cue conflict leading to VR sickness.

Methods

There are various methods of 3D tracking.

3D tracking can be done using multilateration with pointed laser interferometers.

Electric field sensing

There are various types of electric field sensing 3D tracking systems: including capacitive spatial tracking, which uses the same principle as 2D touch screens.

Additionally, electrostatic distance measurement based on field strength is an option.

A more advanced option is Quasi-Static AC Electric Field Ranging or Narrowband AC Electrostatic Fieldmetry, where a source emits an oscillating field in the kilohertz range which the receiver filters out using a bandpass filter and measures the strength of.

Multilateration

The first class of spatial 5DOF or 6DOF tracking methods is those that use multilateration. This includes methods that use time-of-flight measurements of radio signals, such as visible light or ultra-wide band, or alternatively, ultrasonic acoustic signals.

• UWB tracking
• Ultrasonic tracking

Triangulation

This method uses the angles of signals, and is similar to multilateration.

It can be done using phase difference of arrival (PDOA) in UWB.

The human brain uses acoustic phase difference of arrival for sound location, which can be imitated in an acoustic system.

Perspective n-point

The second class of methods is those that use perspective n-point calculations from a camera image.

• Marker-based tracking - Camera based tracking that uses markers in the environment, which is simpler to implement.
• Markerless inside-out tracking, which is a form of camera-based tracking (SLAM/VIO)- This is used on headsets such as Meta Quest headsets and the Project North Star. An open source method is Basalt. Markerless inside-out tracking can use visible light or infrared light, which can be artificially emitted.
• Infra-red based pnp tracking

See List of camera-based tracking methods

Electromagnetic

A third class of methods is those that use field strength of magnetic coils (electromagnetic tracking). Electromagnetic tracking gets jittery when there is metal around, depending on the type of tracking used.

Laser positioning systems

See laser positioning system.

HRTF

A fourth class of methods is those that use an inverse head-related transfer function (HRTF).

Phase based

Phase-based ultrasonic tracking was used in Ivan Sutherland's original head-mounted display, but for rotation only.

Mechanical

Mechanical tracking can be done with an articulated arm 3D input device.

History

The first kind of 3D tracking for computers was acoustic tracking in the 1960s: Lincoln Wand.

See also

• List of 3D tracking companies

References

• Karaseitanidis, Ioannis; Amditis, A. (2008). "A Novel Acoustic Tracking System for Virtual Reality Systems". Product Engineering. Dordrecht: Springer Netherlands.

• Chris Hand. A survey of 3-D input devices. Technical Report TR94/2, Department of Computer Science, De Montfort University, UK, 1994.