GPS WARNING!!

Yesterday I ran my first 10k since I injured myself two months ago. I set off on my regular, favourite route, telling myself that speed was not called for, just steady recuperative kilometres back on them legs. I use Runkeeper, because I carry my phone for music and also track the run with my Crane (Aldi) GPS watch. Both of these tracking systems have given me some odd results at times, so they are there to keep a check on one another, but I have never before had the problem that I encountered yesterday.

As I said, a steady run on a familiar route, so imagine my surprise when Annabel Runkeeper-Smythe solicitously chirps up after about 900 metres to tell me that I have run my first kilometre in 5.03minutes. She may have been trying to protect me and get me to slow down even more, but I wasn't fooled, since I knew I was running at approximately 6m/k, which the watch duly confirmed. Maybe just a blip getting started, I thought, but no, the second kilometre was announced in her caring Mary Poppins style, long before I reached 2k.

This continued throughout the run, with the difference between my two tracking systems getting greater with each kilometre I ran, although I knew from experience that the watch was giving me the more accurate result. Annabel annoyingly continued to notch off these short distance Ks for the rest of the run, consequently announcing that I had run 10k at 59:13, whereas the watch made me run another 700 metres before I reached the big One Zero at 1:04:03.

So, take heed, two GPS systems can give very different results (and Pbs, perhaps!!), while recording the same run. Runkeeper run: 10.7k: GPS watch run: 10.01k. I know this route and the watch was, this time, accurate, but I fail to understand how, when they are presumably using the same satellites and both giving fairly accurate tracks on the map, they can be so far out on distance covered.

Do we have any GPS geeks out there who can explain this? Is my phone finally defunct?

Keep running, keep smiling.

29 Replies

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  • I so get that... a couple of months ago I did a HM distance with my sone and baby sister. Me and baby sister used the Nike App, and son used Garmin. The results ( we all ran together):

    Me: 2 hours 30

    Baby sister: 2 hours 12

    Leon: 2 hours 10

    hmmmmmmm!!!!!

    Well done on the run, the enjoying it is the main thing, so glad you are ...

  • There was no deviation in time between my devices only distance. Yeah, great to be back up to 10k again.

  • How bizarre ! I use only Runkeeper, so don't really have anything else to compare it with. I am sure there will be someone on here who can offer an explanation.

    Nevertheless , a fantastic achievement , well done. Good to hear you have overcome your injury, and long may it continue xxx

  • Thanks poppypug. In fact I didn't really need to track the run at all, because I know the distance and was only wanting to make sure my pace stayed slow enough, but I controlled that purely by being aware of my breathing. So maybe I should have left the tech at home.

  • Phones are less accurate than GPS watches for a variety of reasons. The most common reason is because a phone has the antennas and phone circuity inside and there just isn’t enough room to include a more accurate GPS sensor. GPS watches have a larger GPS sensor as a critical component; that is what they are designed to do, that and nothing else.

    Phones do not take a continuous recording of your location but do frequent “snapshots” in time. These data points are then connected by the shortest distance between the two points. This is why quick movements, turn arounds or tight turns are often cut off when reviewing phone GPS data on a running app.

  • That's a great explanation and helps me understand why sometimes it's plotted me literally zigzagging across the road (giving me an obviously unrepeatable and unrealistic pb of a km in 3 minutes 20 ... uphill!!!!) and also fairly often cuts the hairpin bend off my route. Interestingly, I walked the route yesterday and was going at a leisurely 13 minutes per km (ish) and it still cut the hairpin bend and other corners off. So in fact I wasn't going quite as slowly, but the speed I was going at didn't make it any more accurate.

  • I've found similar situations in the past, and swanscot is right - phones take snapshots with their smaller GPS chips. And then there'll be times when it can't locate itself (like a hairpin on my regular route) so my phone will cut off the corner whereas my watch records it correctly.

    If the phone can't locate itself, it doesn't record anything.

  • Thanks Swanscot, but I knew the distance was wrong because Runkeeper has tracked me accurately on that route many times and each and every kilometre was short compared to the watch and the actual distance on the ground. The tracks on the map are almost identical and don't account for the variation. Strange indeed.

  • That's very interesting! Thanks!

  • I think the excellent article you plagarised is here:

    runneracademy.com/running-a...

    under "Issues with Running Apps"

    Why not just provide a link ?

  • Thanks for the link. I was just copying what a friend had sent to me a wee while back in response to a similar query.

  • Harsh, Simon!

  • If you are running at places with tall structures (skyscrapers), the GPS signal there may be weak or spotty. That may be one reason why the 2 devices have discrepancies.

  • My route is almost entirely open fields and lanes. I am very familiar with partial loss of signal through tree cover and I have run this route with both tracking systems before and never seen this type of discrepancy.

  • Yes, I had the same thing the other day, Runkeeper saying I'd done a KM in 7.30 mins, yeah right, I wish, in my dreams! I often run the same route, I know a KM is about 250 MTs further down the road. BUT, it had sorted itself out when I uploaded the workout. Another time it gave me the workout summary - TIME 22 minutes, average pace etc etc, but I knew i'd been running for nearer 45 minutes - agian it was correct as far as I could tell when it uploaded to the website.

    It also gave me a total elevation of 1,344 mts one day - Cambridge is as flat as it's possible to be!

    I'm happy with Runkeeper though, overall, I'm an amateur runner who just wants to know I'm making improvements, it's not so very important to be totally accurate.

  • I agree with you Curlygurly, Runkeeper has a basic user friendliness which is easy to live with. I have tried several different trackers and Runkeeper is my favourite and they all are occasionally inaccurate, which is probably down to my phone's inaccuracy. I have never had time issues, only distance and altitude, but as you say near enough for us amateurs, but beware, those PBs might need careful scrutiny.

  • My watch often says fastest pace 5 something. I know that's a lie as its nearly double that. I am no expert but in my logical brain I put it down to NASA using the site the same time as me and I suppose I have to admit their work is maybe more important. Hehe.

  • Amazon had a very cheap Garmin (Foreunner 10) in their daily deals last week (£59). Worth keeping an eye out for it coming around again.

  • I want one so much but I'm allergic to metal :-(

  • Could you wear one over a sweatband maybe?

  • Possibly, it's a good idea! Or even put it in my pocket?

  • I've never tried putting my Garmin in a pocket, so not sure how well it would pick up satellites (at least as well as a phone in a pocket, I guess). But isn't part of the purpose of a watch to be able to see your pace, distance, time, etc? If avoiding skin contact with the metal is the priority then a wrist sweat band should hopefully do the trick and you can still see your stats whilst running. :-)

  • I'm long sighted so can't see a watch without my glasses which I hate running in! I really want one of those watches, but keep going round in the same circles of problems...never mind, Runkeeper works well enough for the moment!

  • I don't know if it applies to the specific watch I mentioned, but you can configure them to only show one piece of data per screen, so the data can be quite big, if that helps. I know a friend of mine uses his like this.

  • I ran a 3 minute KM once! I did need to remove the record from Garmin Connect! :)

    So many reasons that GPS can be out by quite a margin. Chipset in the device, solar radiation, satellites available (you need at least 2 for a 2D position that won't be accurate and I think more than 4 for a more accurate 3D position), trees, clouds, mist in the air, wet trees, dry trees, etc... :) And all the reasons stated above!

    It's also "easier" to see more satellites at different times of the day...

    in-the-sky.org/satmap.php

    I've found the Garmin is "reasonably accurate" but you need to remember GPS is always going to be anywhere from 1 to 50 metres out at any point (and these add up during a run)... It's not perfect... which is why courses aren't mapped out with GPS... :)

    en.wikipedia.org/wiki/Road_...

    I'm pretty confident accuracy is >95% of the time >96%... :) :)

  • Glad your back out there running your 10ks again. I bet it feels really good :)

  • Interesting! Well done on getting back up to 10k.

    Pity though - I've just started using Runkeeper a bit, and was really pleased with my speedy (although rather limited) running. Now I can see maybe it wasn't quite as speedy as I'd thought! I still like Runkeeper though. :)

  • In my experience, greenlegs, all the tracking apps are occasionally wayward, as are the mighty Garmins and even my humble Aldi watch. I rely on parkrun to give me an accurate 5k timing and religiously check any other PB tracking against alternative distance measuring techniques, eg. Google Earth, to look for discrepancies.

  • Okay here goes. By the power of geekdom. Essentially GPS within phones/watches are just SAT/NAVs with lower power requirements and we know that these have been developed for cars. They are not really designed for slow moving objects so that's why they approximate in snapshots. The only realistic solution is to run faster and/or run in straight lines.

    I get this problem when I weave through trees at the park. They do a fair job and you shouldn't expect too much methinks.

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