Positional tracking in VR: what it is and how it works

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Positional tracking is a mandatory requirement for virtual reality to work well. If you have ever wondered what positional tracking exactly means and how it works for the Oculus Rift and the HTC Vive, keep reading.

six degrees of freedomFirst of all, you have to understand the difference between head and positional tracking. Whereas head tracking refers only to the rotation of your head (pitch, yaw and roll), positional tracking actually registers the exact position of the headset in space by recognizing forward/backward, up/down and left/right movement. With addition of the latter, motion-sickness is reduced drastically.

Cheaper VR solutions like Google Cardboard struggle to perform positional tracking due to two reasons: For now, phones simply are not powerful enough to handle positional tracking. Furthermore, using QR codes and cameras to track them is in conflict with the idea of simple, mobile VR. Though, a project called Google Paper allows developers to enable positional tracking in their apps.

Oculus IR-LED camera VR positional tracking

The Oculus Rift and the HTC Vive use completely different technologies to perform positional tracking: While the Oculus Rift DK2 has an IR-LED array on its surface that is tracked by an 60fps camera, the HTC Vive takes advantage of Valve´s Lighthouse-technology. Movement is limited using the Rift, because as soon as not enough LEDs are in the sight of the camera, the software has to rely on the data of the Rift´s sensors. Thus, Rift only is able to track your position as long as you are facing its camera. This is the main difference between traditional VR headsets like Oculus Rift and Project Morpheus and the ones using Valve´s technology like HTC Vive and Gameface. If you pay attention to the movement besides rotation in the following clip, you will see that the Oculus Rift DK2 works surprisingly well though:

However, Valve´s Lighthouse floods your room with non-visible light by using two little boxes, which are equipped with LEDs blinking 60 times per second. Every time the LEDs blink, one of two spinning lasers sweep a beam of light across the room. The HTC Vive is covered with little photosensors that detect the flashes and the laser beams, and simply counts the interval between registering them to determ the exact room position of its user:

Valve´s Lighthouse VR HTC Vive

As a result, you can walk around in a 15ft by 15ft (4.5m by 4.5m) area and your position will always be tracked precisely. Further, you do not have to worry about running into something using the HTC Vive, since its cameras identify walls and objects and thus a grid pops up warning you of hitting them when you are too close.

Which positional tracking system do you prefer? Tell us in the comment section below!