Absolute rotation tracking
Orientation tracking is tracking that tracks the rotation of a head-mounted display or other device. It is 3DOF if done in all axises.
It can be done with a combination of an IMU and a magnetometer. The magnetometer senses the earth's magnetic field to give an absolute measurement.
EgocentricEdit
Egocentric orientation tracking is a type of tracking that tracks an object's orientation using only data that comes from the object itself without any external sensors. It can be used to track a head-mounted display.
Egocentric orientation tracking can be used to track a person's head, or it can be used to track a handheld controller or other object.
Egocentric orientation tracking can be done using an IMU that tracks rotational acceleration in three degrees of freedom: pitch, roll, and yaw. The three axes are also known as nodding, tilting, and shaking, as in what a person's head can do.