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Running Apps Discrepancies

1 watcher
Sep 2016
10:24am, 30 Sep 2016
2129 posts
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Tim of MK
I've got "Fitness 22" and "Map My Run".

They both measure one particular route as 4 miles. I know rhis to be 100% accurate.

On another route though, one measures 6.2 miles and the other 6.5 miles.

How can thia be?,
Sep 2016
10:30am, 30 Sep 2016
669 posts
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Stewie
I had the same problem when I lost my Garmin 305 and had to use my iphone, Stava, Endomondo and MotionX all gave different readings and when I replaced the 305 with a Forerunner 10 I discovered all 3 were over reading by at least 10% but each gave a different reading every time, annoying !
Sep 2016
10:31am, 30 Sep 2016
960 posts
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decorum
Only a 0.3 mile discrepancy? Ressult!

The app I use can be less accurate than that on repeats of the same route :-o .
Sep 2016
10:32am, 30 Sep 2016
29 posts
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zolluppepe
It's probably due to how often the app samples your position (ie gets a gps position), or an inexact conversion from longitude and latitude to linear distance, or rounding error, or a bug, or some combination of all 4.
Sep 2016
12:38pm, 30 Sep 2016
10435 posts
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Seratonin
I have two garmin devices a 205 and a 10. I noticed that they can measure different distances - not hugely but still different.
Sep 2016
3:11pm, 30 Sep 2016
3532 posts
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chunkywizard
GPS is inherently inaccurate. Take that with different sampling frequencies and you get distance differences. Google it and you'll get a lot of technical stuff which basically say, your GPS won't be spot on all the time.
Sep 2016
7:24pm, 30 Sep 2016
1076 posts
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Weean
I noted this in a couple of blogs: http://www.fetcheveryone.com/blog-view.php?id=52453&y=2014&m=2 and http://www.fetcheveryone.com/blog-view.php?id=52453&y=2014&m=3

I nowadays tend to run with both Runkeeper (seems reasonably accurate and has good control over alerts) and Wahoo fitness (actually talks to my HRM but always measures long).

chunkywizard explains why quite well.
Sep 2016
7:33pm, 30 Sep 2016
12248 posts
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Dvorak
How are your map traces? Can you see differences?

I've walked the last two nights (not the same course) and whilst tonight's trace is probably one of the closest to route taken I've seen, last night's went quite off over around 700m of the route (it took a shimmy, then traced around the right line, but in the wrong place, then corrected its position).

Although with the phone taking the signal and the apps using I suppose basically the same data (I know naught of the technicalities of such), your case seems a bit odder.
Sep 2016
7:36pm, 30 Sep 2016
7721 posts
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Badger
They're getting the same GPS values from the phone, but they may well be filtering/smoothing them differently, dealing differently with points that look suspiciously far away from the points just before and after, and so on.
May 2021
12:52pm, 21 May 2021
23 posts
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EatSleepRunRePete
Your using the same GPS device (your phone) to record your activity. The difference on different routes could be down to inherent GPS inaccuracies, line-of-sight issues (such as cover, tall buildings, and even weather). The difference on the same route will most probably be down to exactly how each app interprets the GPS plot points given to it (or rather read from the sensor).

So if that 4 mile route has good "GPS visibility" then it will probably always get a good steady stream of GPS plot points and both apps will always measure it accurately.

If on the other hand, that 6.x mile route was done in poor weather, or has tree cover or tall buildings on it (or your phone received a text message at the exact same time it was supposed to be reading the next GPS plot point?! *I don't know if this affects anything, but I'm using it to make a point that your phone has other things to do that could potentially interfere with what you would like it to concentrate on :P), then you might see inaccuracies creeping in.

Finally, phone GPS is only accurate to within 5-10m 95% of the time. I think activity trackers are slightly more accurate (about 3-5m), but we are talking about recreational grade GPS ... this isn't military-grade stuff that can read the cooking instructions on a packet of rice from space ;)

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About This Thread

Maintained by Tim of Fife
I've got "Fitness 22" and "Map My Run".

They both measure one particular route as 4 miles. ...

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