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Geolocation Strategies

Surprisingly often you'll find yourself needing to know the physical location of a user - be it to calculate which time-zone they're in, when the sun sets, or even which building they're in for a guided tour. Such a question has multiple different answers and ways of approaching it, so I decided to blog about the ones I can think of for future reference.

Location-By-IP-Address

The first method that comes to mind is doing a lookup based on the user's IP address. This gives city / area / country level accuracy, which should be good enough for sunrise and sunset times, time-zone information, and so on. Several websites exist that provide this as a service - ipinfo.io comes to mind. You can even do this in the terminal:

curl https://ipinfo.io/ | jq --raw-output '.loc'

(You'll need jq installed to use this. Most Linux distributions come with it in their repositories!)

If a web service doesn't suit you, then several downloadable databases exist. Most you have to pay for to get the 'full' (and most accurate) version, but the free versions available seem to be pretty good up to country / time-zone level. Here are a few I've found:

Precision Matters

If you need something more precise (say for a driving-tracking app or something), then GPS is usually the way to go, although phones are the only device that commonly carry a sensor. Despite the name, GPS actually refers to just a single satellite constellation that was launched by the USA.

Others exist too, of course - Russia have GLONASS, China has BeiDou, and the EU now has Galileo just to name a few. Most phones will support at least 2 from this list out-of-the-box. There's a great app available for Android if you'd like to play around and explore your phone's GPS capabilities.

Utilising a device's GPS support is usually just a case of finding the appropriate API (and, in some cases, permissions) for your environment. For the web, there's the Geolocation API (note that it's for HTTPS websites only). On Android, there's android.location apparently.

Bring in the big data

GPS can be slow at getting a fix, and drain your users' battery. It also has issues in indoor environments. Thankfully, there's an alternative: WiFi-based location mapping. Though it only works where there are WiFi hotspots about (urban areas are best), it is much faster and doesn't use nearly as much power.

Pioneered by Google with their Google Play Services Location API, it sends a list of the strongest WiFi access points (their MAC addresses & signal strengths) that the device can detect off to a remote server, and, after consulting it's massive database of WiFi access points and their locations, it responds with a triangulation of the user's approximate location.

Of course, you probably don't want to be giving Google your location on a regular basis just to save battery power. To this end, Mozilla (the company behind Firefox!) has built their own crowd-sourced location service. Creatively named the Mozilla Location Service, it's continually improved by users of Firefox on their Phones who submit their location along with the detected WiFi networks for analysis on a semi-regular (and automated) basis. There's even a map showing the current coverage!

If WiFi isn't for you, then don't despair! The mobile network (1/2/3/4G) cell towers can also be used - if you've got the right kind of device (sorry, desktops). Databases of cell tower locations exist that can be used to triangulate a user's approximate position.

If you've got a limited indoor area that's already got WiFi that you need to cover, it shouldn't be too time-consuming to manually construct your own database instead.

For example, in a tour-guide Android app you could record the signal strengths in the pre-set locations that you want to take people in your tour, and use a Neural Network (libraries exist!) to decide which one the user is closest to by comparing the signal strengths & MAC addresses of the top 3 WiFi access points in the area.

Bluetooth to the rescue!

If that's still not good enough (say if there aren't any WiFi networks around), you'll probably have to start deploying some of your own infrastructure. Bluetooth beacons are a good place to start. In short, a bluetooth beacon is simply a Bluetooth device that advertises it's presence on a regular basis, along with both it's actual position and the transmitting power that it is currently using to advertise itself. By triangulating the signal from 2 or more beacons, the user's position can be determined.

Of course, this requires that you have a bunch of Bluetooth beacons to hand, which aren't exactly cheap! You could, of course, build your own with an Arduino, but there are still the parts to buy there.

Other worthy contenders

That just about covers all the main geolocation methods I can think of, though there are few others I've come across that sound interesting - but aren't particularly useful unless you've got some specific circumstances.

The first of these is eLoran. Similar in structure to GPS, eLoran has ground-based transmitter stations instead of space-based satellites. It's mainly used by ships at sea and aeroplanes, but I'm sure that it's used elsewhere too. Of course, you need a special receiver chip (and aerial, I should imagine) to use it.

Secondly, there's some research ongoing into utilising LoRa gateways to geolocate a device. I've blogged about LoRa before (and might do again now that I'm actually getting really close to having a pair for RFM95 chips working!) here and also here. There's a blog post (not written by me) explaining geolocation via LoRa here, but it's basically the same kind of thing as above with WiFi, GPS, eLoran, and mobile cell towers.

Conclusion

We've covered practically every geolocation method I can think of - from coarse IP Address-based solutions to much finer GPS and WiFi-based technologies. There are certainly more of them than I thought - each with its own benefits and drawbacks, making different technologies useful in different situations.

Found this interesting? Got another method I haven't thought of? Comment below!

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