3-DOF VS 6-DOF Explained

There are various factors that determine whether a VR headset is suitable for you or not. Consider, for example, the resolution of the headset or the field of view. But the way of tracking can also distinguish a VR headset. Some headsets can be put on directly and you start playing immediately, while other headsets require a complex setup. But how exactly do the methods of tracking work? And what are the advantages and disadvantages?

Most mobile headsets - with the exception of the Oculus Quest and Vive Focus Plus - use rotational tracking (3 DoF). With these headsets, you can look up and down, left and right, and you can tilt your head. But if you try to lean forward or backward, or move the position of your head, this movement is not tracked. In this case, the entire virtual world moves with you, instead of you moving in the virtual world. The same applies to the controllers.

For seated VR content this is no problem, but when you want to use a VR headset with room-scale, this breaks the immersion. After all, you cannot walk around in the virtual world or use your hands to do something.

VR headsets that you connect to a computer, and the aforementioned Oculus Quest and HTC Vive Focus Plus, use positional tracking (6 DoF). With this, the user can actually move through the virtual environment. If the room allows it, you can even walk through the room (room-scale). If the controllers are also 6 DoF, you can directly interact with virtual objects. After all, you can move your hands from top to bottom and from front to back, allowing you to make all the movements you would make in the real world.

• Oculus Go;
• Google Cardboard;
• Samsung Gear VR;
• Google Daydream.

• HTC Vive Pro & Pro Eye;
• Oculus Rift S and Oculus Quest;
• Valve Index;
• WMR headsets.

Rotational 3 DoF tracking is always done with a gyroscope. But positional 6 DoF tracking is a bit more complicated. There is no industry standard for the 'perfect' way of positional tracking. That's why almost all VR headsets use a different form of tracking. The different forms of tracking bring different advantages and disadvantages. Consider the cost, the ease of setup, the size of the tracking environment, and compatibility with other VR systems.

A few years ago, Oculus Rift was one of the pioneers of virtual reality. The goal was to make a good VR headset at a relatively low price, so consumers could enjoy high-end VR quality. The competition, such as HTC and OptiTrack, was priced a lot higher.

The Oculus headset and controllers have a number of infrared LED lights under the plastic. The external sensors that you use when setting up the Oculus Rift can see these LED lights and send this information to the computer software. This allows the computer - and thus the VR game - to know exactly where the Oculus headset and controllers are in the room. The new Oculus Rift S now uses a different method of tracking, but still uses the same method to follow the touch controllers from the headset.

Playstation VR works - just like the Oculus Rift CV1 - with camera sensors, but unlike the Rift, PSVR uses light spectrum tracking. The Playstation 4 'camera bar' contains two sensors placed apart. The camera is connected to the Playstation, which uses the image data to track the blue light strips on the headset and the light spheres on the controllers.

Base stations - also known as lighthouses - are placed at opposite upper corners of the room. They emit a laser beam over the entire room. This happens one axis at a time, so repeatedly from left to right, and then from top to bottom. For each movement, they emit a powerful IR light flash.

The VR headset and the controllers contain a chip that measures the time between the IR flashes and the hitting of the laser swing on each axis. In this way, position in a large space can be determined very accurately.

With inside-out tracking, there is a camera in the headset. This camera views the entire room and can make an accurate estimate of where the headset and the controllers are based on the room.

To track the controllers, the systems work 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 pick up this light and knows where the controllers are.