Positional tracking

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Positional tracking tracks the absolute position of the HMD, hands and other devices and body parts within the 3 dimensional space. Positional tracking records the translational movements, left/right, forward/backward and up/down, of your device. Precise and low latency positional tracking is essential to have a good VR experience and produce presence.

By contrast, rotational tracking, records the rotational movements of your HMD, such as turning and tiling of your head.

Methods

Acoustic

Acoustic tracking measures the length of time of an acoustic signal takes to reach various receivers.

Acoustic tracking can be influenced by surrounding noise causing inaccurate measurements. It also demands careful calibration and does not provide high update rates. Even with its faults, acoustic tracking can be used injunction with other methods to improve positional tracking.

Inertial

Inertial tracking is performed by accelerometer and gyroscope. Accelerometer measures the linear acceleration while gyroscope measures the angular velocity.

While accelerometer and gyroscope supply low latency and high update rate. They do not provide positional information accurately.

Magnetic

Magnetic tracking determines the strength of the magnetic field in different directions.

Magnetic tracking is utilized in Razer Hydra. It is usually a very accurate tracking method, although it can be influenced by magnetic fields generated by other electronics and objects near the sensor or emitter.

Most HMDs and smartphones contain magnetometers, IMUs that detect the magnetic field of Earth.

Optic

Marker

Optical tracking with mark consist of adding an unique marker onto an object you want to track. Then use a camera or multiple cameras to follow the movement and position of the marker. Finally algorithms are used to figure out the position and orientation of the object.

Depth Map

Sensor Fusion