Inside-out tracking
From Virtual Reality, Augmented Reality Wiki

- See also: Marker-less, Inside-Out Tracking and Positional tracking
In inside-out tracking, the tracking camera is placed on the device being tracked such as an HMD. The device looks out to the world around it and uses the changing perspectives of the outside world to determine its own position in space. Fiducial markers such as QR codes can be placed in the outside world to serve as reference points for the tracking camera.
The opposite of inside-out tracking is outside-in tracking.
Devices using inside-out tracking
See Devices using markerless, inside-out tracking
Inside-out tracking systems
See Systems using markerless, inside-out tracking