The tracking devices are the main components for the VR systems. They interact with the system’s processing unit. This relays to the system the orientation of the user’s point of view. In systems which let a user to roam around within a physical space, the locality of the person can be detected with the help of trackers, along with his direction and speed.
The various types of systems used for tracking utilized in VR systems. These are a follows:-
- A six degree of freedom can be detected (6-DOF)
- Orientation consists of a yaw of an object, roll and pitch.
- These are nothing but the position of the objects within the x-y-z coordinates of a space, however, it is also the orientation of the object.
These however emphasizes that when a user wears a HMD then as the user looks up and down; left and right then the view also shifts. Whenever the user’s head tilts, the angle of gaze changes. The trackers on the HMD describe to the CPU where you are staring while the right images are sent back to the screen of HMD.
All tracking system consists of a device that is capable of generating a signal and the signal is detected by the sensor. It also controls the unit, which is involved in the process of the signal and sends information to the CPU. Some systems ask you to add the component of the sensor to the user (or the equipment of the user’s). If this takes place, then you have to put the signal emitters at certain levels in the nearby environment. Differences can be easily noticed in some systems; with the emitters being worn by the users and covered by sensors, which are attached to the environment. The signals emitted from emitters to different sensors can take various shapes, including electromagnetic signals, optical signals, mechanical signals and acoustic signals.
The Tracking devices have various merits and demerits:-
- Electromagnetic tracking systems – They calculate magnetic fields generated by bypassing an electric current simultaneously through 3 coiled wires. These wires are set up in a perpendicular manner to one another. These small turns to be an electromagnet. The system’s sensors calculate how its magnetic field creates an impact on the other coils. The measurement shows the orientation and direction of the emitter. The responsiveness of an efficient electromagnetic tracking system is really good. They level of latency is quite low. The drawback is that whatever that can create a magnetic field, can come between the signals, which are sent to the sensors
- Acoustic tracking systems – This tracking system senses and produces ultrasonic sound waves to identify the orientation and position of a target. They calculate the time taken for the ultrasonic sound to travel to a sensor. The sensors are usually kept stable in the environment. The user puts on ultrasonic emitters. However, the calculation of the orientation as well as position of the target depending on the time on the time taken by the sound to hit the sensors is achieved by the system. Many faults are shown by the acoustic tracking system. Sound passes by quite slowly, so the update’s rate on a target’s position is naturally slow. The efficiency of the system can be affected by the environment as the sound’s speed through air often changes depending on the humidity, temperature or the barometric pressure fousnd in the environment.
- Optical tracking devices – These devices use light to calculate a target’s orientation along with position. The signal emitter typically includes a group of infrared LEDs. The sensors consist of nothing but only cameras. These cameras can understand the infrared light that has been emitted. The LEDs illuminates in a fashion known as sequential pulses. The pulsed signals are recorded by the camera and then the information is sent to the processing unit of the system. Data can be extrapolated by this unit. This will estimate the position as well as the orientation of the target. The upload rate of optical systems is quite fast which has in fact reduced the tenancy issue. The demerits of the system are that the line of sight between an LED and camera can be obscured, which interferes with the process of tracking. Infrared radiation or ambient light are also different ways that can make a system useless.
- Mechanical tracking systems – This tracking system is dependent on a physical link between a fixed reference point and the target. One of the many examples is that mechanical tracking system located in the VR field, which is indeed a BOOM display. A BOOM display, an HMD, is attached on the rear of a mechanical arm consisting 2 points of articulation. The detection of the orientation and position of the system is done through the arm. The rate of update is quite high with mechanical tracking systems, but the demerit is that they limit range of motion for a user.