A couple of inches? Realistically, cameras. Lots of cameras and some OpenCV to do the distance calculations. Bluetooth triangulation is very hard (don't ask me

A couple of inches? Realistically, cameras. Lots of cameras and some OpenCV to do the distance calculations. Bluetooth triangulation is very hard (don't ask me how I know) and won't get you that kind of resolution. Apple's AirTags won't either. Dots painted on the floor at regular 1 yard or 10 foot intervals, in view of the cameras so that calculations can be inferred? Now we're getting somewhere. The good news is security cameras have existed for a long time, and you can almost certainly find someone to bulk purchase from on the cheap. If you insist upon using a wearable you may be able to get a light source on everyone you can calibrate towards. I'm not sure whether that's very helpful in practice.