Ask HN: Best technologies to track location of people in a large building?

If I had a say 50,000 sq ft. Building that had up to 1000 people on it at one time. What is the best way to track where each of them are down to a couple inches accuracy. I’d also love to be able to get the direction they are facing as well. This tracking would of course be opted in and I assume would require some hardware that the person wears.