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No, we simply match tags with the WiFi fingerprint of a particular location. Therefore, there is no need to know the location of the WiFi access points.
A WiFi fingerprint is the pattern of signal strengths of a collection of WiFi access points visible in a particular area. This signal strength pattern tends to vary from place to place, that is how tagin! can attach tags to different locations (e.g., rooms) even when they are covered by the same group of WiFi access points.
Yes, but GPS devices need a clear line of sight to the GPS satellites, so their performance is reduced in shaded environments. In fact, most GPS devices don’t work indoors. tagin! does not have this requirement, so it can be used to tag both indoor and outdoor locations.
Google/Skyhook/iPhone already offer WiFi-based positioning that works indoors. What is different about tagin!?
The WiFi-based positioning offered by Google/Skyhook consists on matching WiFi access points to GPS coordinates, but they only do this at street level. tagin! can be used to tag locations in different floors inside a building, which to Google/Skyhook, would all look as the same location. In other words, with tagin! you can tell the difference between a tag in your floor and one right above or below you.
That usually happens if you do “active” scans, which by the way, also break your internet connection. We only do passive querying of the WiFi access points and try to take advantage of the querying infrastructure already available in the devices. Most laptops and smartphones already do a passive scan every few seconds as part of the usual WiFi connection logic, so when we hook into this, we really just become another app running on the device.