This is part of my ongoing obsession with cool projection stuff, here's a paper from before I was born on some fascinating tracking and interaction methods!

That variable-frequency thing is clever. In a sense it’s similar to how old-school light pens worked: a light sensor can determine its position using a position-varying signal. But: I can’t think of a situation where you’d be better off with this system than with Dynamicland-style fiducial tracking, given that this requires custom projectors (eep!) and active (wired or battery-powered) targets (yuck!).

Really need to bump up the FPS on this. About 10x