They are error-detecting and error-correcting digital signage that gives you precision 6dof orientation “for free.” (And you can do even better... can stick a bunch of them all over a deformable object to map back the shape and deformation.... without lengthy registration and with only a single camera... unlike vidicon) And they’re easy to implement in software. Can be extremely fast (<10ms... no real limit as you can implement it in an FPGA) and fairly lightweight and can use basically any kind of digital camera (good or bad).