Thursday, July 19, 2012

WiFi positioning algorithms

Since version 1.0.3 WiFiLine allows you to select positioning algorithm on the Settings screen. This feature is mostly for advanced users, and appeared due to the fact that WiFiLine is still in beta. Currently the following 3 positioning methods are available:
  • Minimal fingerprint;
  • Extended fingerprint;
  • Synthetic probability;
The second one is enabled by default, and this is the same method that was used in versions prior to 1.0.3.

The fingerprinting is a conventional algorithm for WiFi positioning, which calculates differences between WiFi signal levels in map points and current user device's measurements, and selectes a point with minimal error. You can find more details in Wikipedia.

The probability method utilizes a wellknown Bayesian theorem for calculating probabilities to get current signal levels in map points, and selects a point with maximal probability. As the method implies, the more measurements have been taken during map creation (20 is the greatest allowed value so far), the better accuracy can provide this method. If you select a few scan number in settings (1 - 5) while preparing a map, the probability method will most likely fail afterwards. Once a map is created with a sufficient number of scans, the scan count setting is not so important for location itself.

In future more methods are planned to be added. As they will use more sophisticated algorithms, I think they will allow WiFiLine to improve location accuracy.

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