Indoor triangulation/navigation via wifi possible?

Question

WiFi

In theory, everything is clear - with sufficient coverage of the area by the routers and knowing the exact coordinates of the routers, you can either read the power of the nearest routers on the phone and position yourself, or read the power of the phone in the routers, transfer it to the server and position the phone using the summary information from the routers. But in practice? How to read the signal strength of the phone on the router? Router on the phone (iOS for example)? What router models to use? What software? Are there ready-made solutions at a price cheaper than an airplane? Does anyone have alienable and salable developments?
Why wifi and not GPS\RFID\iBeacon\opsos bs? Because the only thing that works with the highest possible probability in the premises under consideration and for users on their phones is WiFi. GPS is not visible, BS will not allow triangulation indoors, RFID is generally xs how to read, beacons require bluetooth, which is turned off for users.

Answer 1

Cisco - Positioning in Wi-Fi networks with high accuracy.