>>407925538
>https://www.youtube.com/watch?v=J54dotTt7k0
>tl;dr black magic
Each basestation sweeps a laser across the room vertically and horizontally, that is detected by lots of tiny sensors on the tracker.
Depending on the orientation and position of your tracker, the laser sweep will hit each sensor on the tracker at slightly different times, or not at all.
Given the known shape of the tracker and the layout of the sensors on it, you can calculate where the tracker would have to be relative to the basestation for the sensors to have detected the laser with timing they did.