> Or the bin’s precise location - how many fixed reference points would I need to triangulate it on a 2D plane?

Back in 2019 I worked for a company (in San Diego) that added UWB-based positioning to the 7 train line in NYC.

The code I wrote ran on what was basically a combined Raspberry Pi 3 compute module connected to a UWB device installed into the train's bonnet which would ping UWB devices set along the track side to determine the position of the train.

In most situations I could get a unique position based on only two beacons, but I had the benefit of the trains being on one of a limited number of fixed tracks which severely limited where they could practically be in space... well, assuming there hadn't been a train derailment.

The system didn't work in a 2D plane, though, our surveyed track data and track side UWB positions were all 3D encoded as ECEF coordinates.

In some situations depending upon track layout you needed more than 2 beacons to determine the correct position if you were just sampling single points in isolation, but since you're working with a continuous stream of changed positions as the train ran along the track at predictable speeds, you could pretty easily figure out which of multiple possibilities it had to be based on what came before even if you had potential multi-positional results for the current sample.

Of course, we would use as many of the track side beacons as we could see to strengthen confidence in the positioning, and the beacons were placed so we could generally see a good 4-6 of them most of the time.

Snow was the biggest challenge for the system, in a heavy thick snow the UWB signals bounce all over the place and you get severe multipath effects that can make it pretty difficult to determine which is the true line of sight signal for your time of flight calculations.

Fun job, I had to get certified to be able to walk the NYC train tracks because we installed a lot of the track side beacons ourselves, and I spent a lot of late nights doing live testing runs on trains that were empty other than a couple of people from our company and some MTA workers assigned to our test trains.