Pose tracking
In VR, it is paramount that pose tracking is both accurate and precise so as not to break the illusion of a being in virtual world.
Several methods of tracking the position and orientation (pitch, yaw and roll) of the display and any associated objects or devices have been developed to achieve this.
Many methods utilize sensors which repeatedly record signals from transmitters on or near the tracked object(s), and then send that data to the computer in order to maintain an approximation of their physical locations.
A wireless technology called Ultra Wideband has enabled the position tracking to reach a precision of under 100 mm.
Pros: Cons: Optical tracking uses cameras placed on or around the headset to determine position and orientation based on computer vision algorithms.
Markers can be visible, such as printed QR codes, but many use infrared (IR) light that can only be picked up by cameras.
Markerless tracking does not require any pre-placed targets, instead using the natural features of the surrounding environment to determine position and orientation.
Having multiple cameras allows for different views of the same markers, and this overlap allows for accurate readings of the device position.
[5] The original Oculus Rift utilizes this technique, placing a constellation of IR LEDs on its headset and controllers to allow external cameras in the environment to read their positions.
Pros: Cons: In this method, the camera is placed on the tracked device and looks outward to determine its location in the environment.
Headsets that use this tech have multiple cameras facing different directions to get views of its entire surroundings.
[6] Machine learning algorithms then determine where the headset is positioned within that 3D map, using feature detection to reconstruct and analyze its surroundings.
The direction of Earth's magnetic field can be integrated to have an absolute orientation reference and to compensate for gyroscopic drifts.
[15] Modern inertial measurement units systems (IMU) are based on MEMS technology allows to track the orientation (roll, pitch, yaw) in space with high update rates and minimal latency.
[16] Dead reckoning is used to track positional data, which alters the virtual environment by updating motion changes of the user.
[17] The dead reckoning update rate and prediction algorithm used in a virtual reality system affect the user experience, but there is no consensus on best practices as many different techniques have been used.
Many applications of virtual reality need to not only track the users’ head rotations, but also how their bodies move with them (left/right, back/forth, up/down).
[20] Six degrees of freedom capability is not necessary for all virtual reality experiences, but it is useful when the user needs to move things other than their head.
Pros: Cons: Sensor fusion combines data from several tracking algorithms and can yield better outputs than only one technology.
Combining optical and inertial tracking has shown to reduce misalignment errors that commonly occur when a user moves their head too fast.
[21] Microelectrical magnetic systems advancements have made magnetic/electric tracking more common due to their small size and low cost.
[22] Acoustic tracking systems use techniques for identifying an object or device's position similar to those found naturally in animals that use echolocation.
Analogous to bats locating objects using differences in soundwave return times to their two ears, acoustic tracking systems in VR may use sets of at least three ultrasonic sensors and at least three ultrasonic transmitters on devices in order to calculate the position and orientation of an object (e.g. a handheld controller).
Here, each li represents the distance from the transmitter to each of the three receivers, calculated based on the travel time of the ultrasonic wave using the equation l = ctus.
PC tracking involves comparing the phase of the current soundwave received by sensors to that of a prior reference signal, such that one can determine the relative change in position of transmitters from the last measurement.
Pros: Cons: In summary, implementation of acoustic tracking is optimal in cases where one has total control over the ambient environment that the VR or AR system resides in, such as a flight simulator.
Current, sequentially passing through the coils, turns them into electromagnets, which allows them to determine their position and orientation in space.
The system works poorly near any electrically conductive material, such as metal objects and devices, that can affect an electromagnetic field.
Magnetic tracking worsens as the user moves away from the base emitter,[21] and scalable area is limited and can't be bigger than 5 meters.
