Pop quiz, hotshot. You like geolocation and find it useful, but it doesn’t work well indoors. What do you do? What…do…you…DO?

The first step is figuring out what you would need in order to make this work. GPS-like signals need atomic clocks to keep the signals synchronized to the level that would be useful, since they rely on measuring time delays. Inertial navigation needs, at a minimum, a gyroscope and an accelerometer and a knowledge of your initial conditions. You can then integrate any rotations or accelerations to calculate changes in orientation or speed. But errors kill your precision, sooner or later, because they accumulate as you continue to integrate; your speed is calculated by integrating the acceleration and your position is calculated by integrating the speed, (and similarly for your orientation) so any small error in the acceleration (or rotation) is compounded the longer you travel, and indoor navigation requires a fair amount of precision to be of any use.

What you need is error correction. Orientation is pretty easy — just add a compass to the system and you can always tell which way you are pointing, assuming that a compass is useful, i.e. you aren’t near or surrounded by anything that would disrupt the earth’s magnetic field. Correcting the position requires some adjustment, such as sighting some landmarks and triangulating. This is why prior to GPS and its predecessors, submarines would get a “star fix” when they poke their periscope up above the waves or surfaced (they’d be jonesing for dem stars after being submerged a while), but such correction is at the mercy of the weather. Sighting fixed landmarks also requires a calm ocean for a ship/boat, or the equivalent on land — requiring that you be stopped or having your motion restricted may not be desirable. A beacon of some sort would be helpful.

But who wants to lug around a gyroscope, accelerometer, maybe a compass and a radio receiver of some sort? Well, me, for one. I’ve described the newest version of an iPhone or iPod touch (no compass in the latter, as far as I can tell) and probably other smart phones. The beacon is already present in many locations — WiFi or bluetooth (and it might be possible to use cell phone signals) The AMNH is already doing this: American Museum of Natural History’s Explorer App Makes Paper Museum Maps Ancient Artifacts

[T]he American Museum of Natural History Explorer, an app for iPhones and iPod Touches which uses over 300 Wi-Fi hotspots to triangulate your position inside the museum—a feat of “indoor GPS” the museum claims is the first of its kind, and, if it’s not, it’s the most usable implementation of it I’ve come across—takes the stress out of finding the particular piece of history you’re looking for.

Imagine a searchable map of a mall that you carry around with you, with directions on how to get to the store of your choice. A store matching your shopping list with a map, showing where you are and where the items are.

You can envision turning this technology around, too. You could track where people go (presumably anonymously and with their permission) to get insight into traffic patterns. For limited applications, you might not even need the screen that is offered by a phone; just a transponder that gave the location of some important piece of equipment. What if you are in charge of a building (or building complex), and want to know where key personnel are, such as security staff? Communication with geolocation would allow your guards to communicate and a supervisor at a map screen could coordinate their actions — a version of the Star Trek: TNG communicator seems to be a very achievable goal in the not-very distant future.