Saturday, December 15, 2012

Android and locations - a sad storry

So I am e.g. browsing Google Maps and have a GPS fix. Now I switch to Ingress or c:geo from the recently used apps list. And what happens?

GPS-fix icon in the upper left corner turns off, app changes and I have to wait between 6 and 15sec to get a new fix even if I did not move a centimeter.

Worse is that the position during the switch-over is sometimes kilometers off, as the app uses the location from the network, which depends on the size of the network cell and the location of the next tower. If you are in a location based app, that switchover can even cause additional network traffic as e.g. maps needs to load a new tile or g:geo does the "nearby caches" search in a non-interesting area.

The technical background is the application lifecycle in Android and the recommendations to safe battery just don't mix.
When app one (e.g. maps) is brought to background, the GPS receiver is switched off, then the switchover happens and only after the onResume() has finished, it is turned on again. Unfortunately the Android system itself seems not to cache the GPS info for a little time and offers that to the next app as a potential current location, but just falls back on network location.

A solution could be for the Android system to cache the GPS location and add an uncertainty linear to the age of the fix. So while the location + uncertainty is smaller than the distance from the location obtained from network, the GPS location would be used. And then after the mentioned 6-15 sec, the real GPS data would take over.

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