Nokia Sports Tracker and Jitter
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That is, if the underlying technology worked properly.
On the picture you can see a short trip I did yesterday evening. In real life it's about 3 - 3.5 km in a pretty suburbian area. The GPS weather was bad, so the GPS location kept jumping back and forth all trip, and those jumps were calculated in my overall travel. The somewhat funny end result of all this was that my average speed over this trip was 66.9 km/h, with a maximum speed of 150 km/h, as the total distance - according to GPS - was 34.38 km (that's a tad over 21 miles to all you metric-challenged people). My phone probably now thinks I'm an athletic junkhead giant robot on a particularly bad dose of speed.
Anyway, my point being: GPS, even if you have good equipment (I have a Sirf-III), is not always to be trusted. It works correctly so often, that when it fails, it can spell a catastrophy when you don't pay attention. The human factor cannot be removed either: a colleague recounted a story where he and three friends were trying to find an unfamiliar place, and they all had GPS units. Unfortunately, they all also managed to input the same, wrong, address in the device, and ended up miles away where they were planning to go...
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| "Main_blogentry_280307_1" last changed on 28-Mar-2007 10:21:26 EEST by JanneJalkanen. |
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> and ended up miles away where they were planning to go...or kilometres away for the Imperially challenge :)
--Hugo, 28-Mar-2007
They were in the US ;-)
--JanneJalkanen, 28-Mar-2007
Moi Janne,
I've been running (and biking) with Nokia Sports Tracker also. Previously I used the Nike+ sensor with iPod nano but grew frustrated since it proved very inaccurate. Which is not very surprising, since Nike+ is just an accelometer or something very simple - it seems to give different results if I run on soft or hard terrain, for example.
Now, just to compare the results, I've been running with both, Nike+ and Nokia GPS. Yes, it's a lot of electronics to lug around, but actually not THAT bad. :) The funny part is that the stats they give are all over the place - sometimes Nike+ shows more than GPS, sometimes less. I thought that GPS should be the accurate one, but after reading your post, I guess I need to reconsider. :(
I guess I need to hire somebody to drive a car next to me when I run, seems like it's the only way to get some accurate mileage. :)
--Aki, 28-Mar-2007
Yeah, GPS can sometimes be very accurate. But sometimes the jitter can be very, very bad. My example above is certainly among the worst.
--JanneJalkanen, 29-Mar-2007
Yes, I got the same problem today... I have Nokia LD-3W. Is this common situation? I just switched off the app and continued running.
--AnonymousCoward, 23-Apr-2007
Yes, it's pretty common. Depends a lot on things like space weather and the visibility pattern of the satellites. There are ways to compensate for it (e.g. D-GPS, WAAS, A-GPS), but still, the baseline comes from the GPS satellites.
Some post-processing might also help; obviously, if you're running, you're not going at 150 kph, so maybe someone out there has created a filtering program that can give you better accuracy.
--JanneJalkanen, 24-Apr-2007
There's an update to Nokia Sport tracker thar filters GPS Data: i had the same problem of inaccurate data depending on weather and coverage (running under trees could give same bad results even on a sunny day). With the updated v.1.42 versione you could filter gps data the get better results, even if i noticed a bit of lag when it updates position on calculated perofrmaces.
--Dado_one, 06-May-2007