3-DOF vs 6-DOF explained

There are various factors that determine whether a VR headset is suitable for you, such as the resolution of the headset and the field of view. However, the method of tracking can also set one VR headset apart from another. With some headsets, you can start playing straight away, while others require a complex setup. But how do these tracking methods actually work? And what are the pros and cons of each?

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 tilt your head. However, if you try to lean forward or backward, or move the position of your head, this movement isn’t tracked. The entire virtual world moves with you in this case, instead of you moving within the virtual world. The same applies to the controllers.

For seated VR content, this isn't an issue, but when you want to use a VR headset for more interactive experiences, it breaks the immersion. After all, you can’t walk around the virtual world or use your hands to do something.

VR headsets that you connect to a computer, such as the previously mentioned Oculus Quest and HTC Vive Focus Plus, use positional tracking (6 DoF). This allows the user to actually move around the virtual environment. If space permits, you can even walk around the room. If the controllers also have 6 DoF, you can interact directly with virtual objects. You can move your hands up and down and forward and back, enabling you to make all the movements you would 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;
• HoloLens 2.

Rotational 3 DoF tracking is always done with a gyroscope. However, positional 6 DoF tracking is somewhat more complex. There is no industry standard yet for the ‘perfect’ method of positional tracking. As a result, almost all VR headsets use a different form of tracking. The different forms of tracking come with various pros and cons. Consider factors such as cost, setup ease, the size of the tracking environment, and compatibility with other VR systems.

Oculus Rift was one of the pioneers of virtual reality a few years ago. The goal was to create a good VR headset at a relatively affordable price, so consumers could enjoy high-quality VR. The competition, like HTC and OptiTrack, was much higher in price.

The Oculus headset and controllers have several infrared LEDs under the plastic. The external sensors you use when setting up the Oculus Rift can see these LEDs and send this information to the computer software. This allows the computer and therefore the VR game to know exactly where the Oculus headset and controllers are located in the space. The new Oculus Rift S now uses a different method of tracking but still uses the same method to track the touch controllers from the headset.

Playstation VR works similarly to 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 spaced-apart sensors. The camera is connected to the Playstation, which uses the image data to track the blue light strips on the headset and the light balls on the controllers.

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

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

In inside-out tracking, a camera is embedded in the headset. This camera observes the entire space and can make an accurate estimation of where the headset and controllers are located based on the space.

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 capture this light and thus knows where the controllers are located.