Virtual Reality (VR) Tracking explained
There are several factors that determine whether VR glasses are suitable for you or not. Consider, for example, the resolution of the glasses or the field of view. But also the way of tracking can distinguish VR glasses. Some headsets you can set up right away and start playing with right away, while you have with others headsets to set up a complicated setup. But how exactly do the tracking methods work? And what are the pros and cons of it? In this blog we explain the differences between the tracking systems for you.
What is the difference between 3 DoF and 6 DoF?
Most mobile headsets - with except the Oculus Quest and Vive Focus Plus - use rotational tracking (3 DoF). You can with this headsets look up and down, left and right, and you can tilt your head. But if you try to lean forward or back, or move the position of your head, this movement will not be tracked. The whole virtual world moves with you in this case with, instead of you moving in the virtual world. The same goes for the Controllers.
For seated VR content this is not a problem, but when you want to use VR glasses with room-scale this breaks the immersion. After all, you can't walk around in the virtual world or use your hands to do anything.
VR glasses that you connect to a Computer, and the aforementioned Oculus Quest and HTC Vive Focus Plus, use positional tracking (6 DoF). This allows the user to actually move through the virtual environment. If space permits, you can even walk around the room (room-scale). If the Controllers are also 6 DoF, you can directly communicate with virtual objects. You can move your hands from top to bottom and from front to back, so you can make all the movements you would make in the real world.
Examples of 3 DoF VR glasses are:
- Oculus Go;
- Google Cardboard;
- Samsung Gear VR;
- Google Daydream.
Examples of 6 DoF VR glasses are:
- HTC Vive Pro & Pro Eye;
- Oculus Rift S and Oculus Ques;
- Valve Index;
- WMR glasses.
What tracking methods are there?
Rotational 3 DoF tracking is always done with on a gyroscope. But positional 6 DoF tracking is a bit more complicated. There is still no industry standard for the 'perfect' way of positional tracking. That's why almost all VR goggles use a different form of tracking. The different forms of tracking come with different advantages and disadvantages with. This includes costs, ease of setup, size of the tracking environment and compatibility with other VR systems.
Constellation (Oculus Rift CV1)
Oculus Rift was one of the pioneers of virtual reality a few years ago. The goal was to make good VR glasses for a relatively cheap price, so that Consumers could enjoy high-end VR quality. The competition, such as HTC and OptiTrack, was price-wise a lot higher.
The Oculus headset and Controllers have a number of infrared LEDs under the plastic. The external sensors you use when setting up the Oculus Rift can see these LEDs and forward them Information to the computer software. This allows the Computer - and thus the VR game - to know exactly where the Oculus headset and Controllers are located in the room. The new Oculus Rift S now uses a different tracking method, but still uses the same method to track the touch Controllers from the headset.
Playstation VR works - just like the Oculus Rift CV1 - with camera sensors, but unlike the Rift, PSVR uses tracking in the light spectrum. The Playstation 4 'camera bar' contains two sensors placed apart. The camera is connected with to the Playstation, which uses the image data to track the blue light strips on the headset and the orbs on the Controllers.
SteamVR (HTC Vive, Vive Pro & Valve Index)
Base stations - also called lighthouses - are placed at opposite top corners of the room. They emit a laser beam over the entire space. This is done 1 axis at a time, so repeatedly from left to right, and then from top to bottom. They emit a powerful IR light flash for every movement.
The VR headset and the Controllers contain a chip that measures the time between the IR flashes and hitting the laser sweep on each axis. In this way, position in a large space can be determined very accurately.
Inside Out Tracking (Windows Mixed Reality, Oculus Rift S, Vive Focus Plus)
With inside-out tracking, there is a camera in the headset. This camera views the entire room and can provide an accurate estimate of where the headset and the Controllers are located based on the room.
To track the Controllers, the systems work in the same way as the aforementioned 'constellation'; with visible light or with infrared light under the plastic of the Controllers. The camera in the headset can catch this light and know where the Controllers are located.