Simultaneous localization and mapping
Simultaneous localization and mapping (SLAM) is a technique used for 3D tracking that uses cameras to capture images of an environment and computer vision to determine the pose of the camera(s). It is a kind of egocentric tracking.
It uses one or more cameras that are mounted on a rigid body like a headset.
SLAM has stability problems. If the cameras are covered, the gadget can lose tracking or become erratic.
It operates based on computer vision, heavily relying on feature detection. It is similar in concept to visual inertial odometry (VIO).
One method of SLAM is ORB SLAM2. Another method is ORB SLAM3. Another SLAM-like method is RTAB-Map.
The Hololens 1 and the Magic Leap 1 both use a SLAM-type system for their 3D tracking.
The Oculus Quest 2 uses a tracking system that is some kind of SLAM or VIO.