All entries for Monday 08 December 2008

December 08, 2008

iPhone GPS reliability

There are several fitness-related apps out there now for the iPhone that record running, cycling or other activities and sync them to a website where you can do further analysis, get monthly totals, etc. GPS Tracker, Trailguru and RunKeeper are three such apps I’ve played with recently while out cycling. I like to record every cycle journey and calculate statistics about them, and so these apps should be perfect for me.

The problem is, I can’t rely on them. My cycle computer records every journey consistently. Over the same route I get the same distance recorded, to within a hundredth of a mile, every single time. Every. Single. Time. A GPS track seems to vary in length a little more than that, but not enough to be too much of a problem. The problem is, I don’t always get a complete GPS track recorded. The iPhone seems to loose satellite lock too easily. Take today’s route as an example:

The straight line from Balsall Common to Burton Green should follow the road, but doesn’t. Instead it leaps straight from the A452 to Cromwell Lane for a little while before leaping again straight to University House. There’s not a lot of tree cover on those roads. Less that at other points on the route. Based on my experiments so far, this sort of thing happens on about 25% of my rides. For my purposes, that’s just useless. I carry the phone in the back pocket of my cycling jacket so it should have a reasonable view of the sky.

All the apps I’ve tried do this occasionally, so it seems it has to be the hardware. I’ve also got a fairly basic Garmin handheld GPSr (a Geko 201) that has never done this on a cycle ride. It does lose satellite lock when walking in woods, but on the roads it never does. Does the Garmin have better a GPS receiver than the iPhone. I thought not, but the evidence says otherwise.

As much as I’d love to record every cycle route this way, there’s just no point if it is going to be so unreliable. Sigh…

Addendum: I don’t remember any such problems when using SportsTracker on Nokia devices, over some of the same routes even. Indeed the Nokia E71 I had on trial a little while ago managed to correctly record the whole of the 68 mile MacRide I did back in September. Not a glitch. Maybe I should be hoping that Nokia manage to come up with an iPhone-killer by the time my iPhone contract is up? Christmas 2009 would be perfect timing…:-)


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