tl;dr

Every so often, Twinkle (a location aware Twitter client for the iPhone) thinks I am in Chepstow:

This seems to happen at random, but often enough to be annoying. I’ve seen it half a dozen times, I’ve seen it happen in the just-released Twinkle v1.1, and I’ve seen it happen in work (in Cardiff) and home (in Cwmbran).

If I immediately quit Twinkle and hop over the Maps, the wrong location measurement persists. These screenshots were all taken from my workplace in Cardiff. The screencaps below show the area it thinks I am in, both close up, and zoomed out to show how far out it is — the false reading is about 35-40 miles from Cardiff.

Based on the radius of the blue circle, I’d guess this information is coming out of the iPhone’s WiFi based location system (more details on how this works are here); the circle radius is too small to be derived from cell phone tower triangulation, and if it were a GPS based reading I would see a blue pin and not a circle at all. So a first guess as to the cause of the problem is that it could be duff data in Skyhook’s database of WiFi positions.

But! That wouldn’t be an intermittent error, and would only effect one location; I’ve seen the exact same false position reading when at home and in work, which certainly have very different WiFi networks visible to the phone. Furthermore, a few minutes after this false result I booted Maps up again and suddenly it got my location right:

Note that once again this seems to be based off WiFi positioning (I am a long way indoors, so the iPhone can’t get a GPS signal in the office). I went back to Twinkle after taking this screenshot and it had the right location this time.

I’m not sure what to make of this. Twinkle, as far as I can see, doesn’t do much with the location apart from ask the iPhone SDK for it; certainly, the fact that the iPhone’s native Maps application replicates the incorrect reading suggests it’s a bug in Core Location and nothing to do with Twinkle. However I have only seen this bug appear after using Twinkle — although Twinkle is the only location aware app I’m using regularly on the iPhone. It’s all very odd; what gets me is that it keeps locking me into that very rural area of Wales between Chepstow and Abergavenny.

Edit: seems this problem is being discussed on Tapulous’s support forum.

Personal, Tech, iPhone