Degrees of freedom (Dof) refer to the number of basic ways a rigid object can move through 3D space. There are six total degrees of freedom. Three correspond to rotational movement around the x, y, and z axes, commonly termed pitch, yaw, and roll. The other three correspond to translational movement along those axes, which can be thought of as moving forward or backward, moving left or right, and moving up or down.
VR headsets and input devices are generally 3-Dof or 6-Dof.
Degrees of freedom is an essential concept in VR that allows human movement to be converted into movement within the VR environment.
3-Dof headsets allow us to track rotational motion but not translational. With a user wearing a VR headset, we can therefore track whether a user:
Looks left or right
Rotates their head up or down
Pivots left or right
With 3-Dof, we cannot determine whether the user has moved (translational movement) about the scene by moving in real life.
How is 3-Dof tracking achieved?
3-Dof headsets provide the simplest form of user tracking in VR. It relies mostly on inbuilt sensors (accelerometers, gyroscopes and magnetometers) that devices (such as a smartphone) use to measure movement.
6-Dof headsets allow us to track translational motion as well as rotational motion. We can determine whether a user has rotated their head and moved:
Forward or backward
Laterally or vertically
Up or down
This type of tracking is important for VR experiences with translational motion and gives the user a lot more freedom to explore locations, inspect details and perform real life tasks in VR.
How is 6-Dof tracking achieved?
There are various ways to achieve this. Early versions of 6-Dof headsets typically use positional tracking sensors (usually two physical devices positioned around the room which can track headset movement)