For all of their awesome applications — from portable navigation devices, to self-driving cars, to cruise missile targeting — the American Global Positioning System and its Russian cohort GLONASS have two fundamental flaws: They don’t work indoors, and they only really operate in two dimensions.
Now, these limitations are fair enough; we’re talking about an extremely weak signal that has traveled 20,200km (12,600mi), after all. Passing through concrete and other solid obstacles is hard enough for a strong, short-range cellular signal — you can’t seriously expect a 50-watt signal traveling 12,000 miles to do the same. Detecting a GPS signal on Earth is comparable to detecting the light from a 25-watt bulb from 10,000 miles.
The situation is a little more complex when it comes to detecting a change in altitude; GPS and GLONASS can measure altitude, but generally the data is inaccurate and too low-resolution (on the order of 10-25 meters) for everyday use. Even with these limitations, though, space-based satellite navigation systems have changed almost every aspect of society, from hardware hacking to farming to cartography to finding a girlfriend.
What if we had a navigation system that worked indoors, though? What if we had an Indoor Positioning System (IPS)? Believe it or not, we’re very nearly already there.