Our quick explainer lays out the various differences in positional tracking and Degrees of Freedom (DoF) in virtual reality, as well as how to pick the right headset for your business.

No one ever said that virtual reality wasn’t complicated. As the technology surrounding VR evolves, so the various bells and whistles that simulate the real world become more sophisticated. A major focus in recent years has been in how we can recreate natural human movement in virtual reality and – more importantly – how we can measure it accurately so that a user’s movement in the real world will correspond to an identical change in virtual reality.  

All VR headsets have some form of positional tracking and, although there is a significant disparity between how different models work, their tracking functionality generally boils down into three distinct categories, chiefly distinguished by the ‘Degrees of Freedom’ that they offer.

1.    Three Degrees of Freedom (DoF) – Rotational movement

Headsets that use Three Degrees of Freedom (3DoF) tracking: All phone-based VR headsets including Google Cardboard, Samsung Gear VR, Google Daydream, as well as some standalone headsets such as Oculus Go (released in 2018)

This is the simplest form of user tracking in virtual reality and relies entirely on the inbuilt sensors (accelerometers, gyroscopes and magnetometers) that phones use to measure movement.

In essence, these tools allow a device to measure how it is moving in three types of directional rotation (aka 3DoF). Certain user movements are registered by these sensors and translated so that the VR program running on the phone can respond in real-time.

Degrees of Freedom in VR – roll

Roll is where the head pivots side to side (i.e. when peeking around a corner)

Degrees of Freedom in VR – Pitch

Pitch is where the head tilts along a vertical axis (i.e. when looking up or down).

Degrees of Freedom in VR – Yaw

Yaw is where the head swivels along a horizontal axis (i.e. when looking left or right)

2.    Six Degrees of Freedom (DoF) – Rotational and Translation movement

Headsets that use six Degrees of Freedom (6DoF) tracking: PC-based headsets including Oculus Rift, HTC Vive, Windows Mixed Reality.

A more sophisticated version of positional tracking is Six Degrees of Freedom (DoF), which incorporates the three rotational measurements (rolling, pitching and yawing) and adds three further directional movements that allow a person to physically move around in a virtual space, rather than simply standing in one spot.

This type of tracking is crucial for whole-room VR experiences and gives the user a lot more freedom to explore locations, inspect details and (perhaps as crucial) to dodge virtual bullets.

With Six Degrees of Freedom (6DoF) both the headset and the controllers worn by the user are tracked. This can be achieved either by using external sensors to capture movement (known as outside-in tracking) or using sensors attached to the headset itself (called inside-out tracking) which continuously relays the positions of the headset and controllers back to the computer.

Degrees of Freedom in VR – Elevation

Elevation is where a person moves up or down (i.e. when bending down or standing up)

Degrees of Freedom in VR – Strafe

Strafe is where a person moves left or right (i.e. when sidestepping)

Degrees of Freedom in VR – Surge

Surge is where a person moves forwards or backwards (i.e. when walking)

3.    Three and Six Degrees of Freedom (DoF) – Hybrid tracking

Headsets that offer varying Degrees of Freedom tracking: Stand-alone headsets including HTC Vive Focus and Lenovo Mirage Solo (to be released in 2018).

With a number of wireless headsets on the horizon (click the link for more on what the next generation of VR headsets will look like), attention has turned to a hybrid positional tracking system, whereby the headset offers Six Degrees of Freedom (6DoF) but the controllers can only recognise Three Degrees of Freedom (3DoF).

This reduction in handheld controller tracking is a result of prioritising the movement of the headset (which is crucial to a better user experience) and, although it won’t offer quite the same functionality as a 6DoF controller, it does allow standalone VR to offer an almost-comparable experience while reducing the amount of processing power required to track the user.

Only a couple of headsets have been announced with this ‘hybrid’ approach to positional tracking, although this is likely to grow in popularity as more and more wireless standalone headsets reach the market.

Picking the right headset for your needs 

Deciding on which type of headset you need will inevitably depend on the end application your business needs it for. For a stationary experience such as a VR technology demonstration or viewing a home being sold off-plan, a 3DoF headset might be suitable. However, for any VR experience where the user needs to have the freedom of exploration, 6DoF tracking becomes a necessity.

It is always worth discussing your needs with your VR design team before specifying one approach or the other, as they might be able to find an innovative solution for what you're looking to achieve.