Geomagnetics for indoor positioning
Magnetic positioning - monitoring the local magnetic field within a building - appears to give remarkably accurate location.
Each building or structure has a unique magnetic 'fingerprint', based on the way building materials affect and distort the otherwise constant Earth's magnetic field. These patterns of distortions can be precisely assigned to a building floor plan, enabling smartphone owners to be located within the likes of shops, hospitals, malls, airports and stations to within 1-2 m.
Such an indoor positioning system (IPS) utilises the built-in magnetic sensor - the compass - as well as other sensors (such as an altimeter) within a smartphone, to locate its position within a pre-surveyed magnetic map. Software plots the indoor location in the same way that a GNSS app would do outdoors.
No infrastructure is required within a building - just an accurate survey undertaken - but positioning can be further refined with such as WiFi and beacons if available.
Leaders in the technology are IndoorAtlas - their website can be found at the link below . .