Running with GPS. Why is the distance so inaccurate?

Discussion in 'Apple Watch' started by plantoschka, May 10, 2015.

  1. plantoschka macrumors member

    Apr 23, 2015
    I have an Apple Watch Sport since the 24.04.
    I used the watch to track a lot of workouts (running, cycling). I noticed during my first runs that the distance at the end was like 5-10% shorter than on Runtastic or Runkeeper. I ran this track a lot of times so I'm pretty sure that it is around 8KM.

    I always took my iPhone with me so that the Watch could use the GPS on the Phone.

    So in the last couple of days I went on three runs on the same track:
    1. Apple Watch + iPhone (IMG_0119)
    2. Apple Watch without iPhone (IMG_0118)
    3. iPhone with Runtastic (Screenshot ...)

    I attached a photo of each run to this post. It's in German but you should get the data.

    It cleary shows me the Apple Watch without the iPhone is more accurate than with the iPhone. How can this be? It's absolutely ridiculous. Tracking the distance without GPS is probably much harder.
    Both are still shorter than the Runtastic data.

    So Apple got the hard thing pretty good but messed up the easy thing? How can this be?

    Of course the messed up distance tracking also messes up my pace (time per km).

    Also the activity calories are way lower than data on Runtastic. Runtastic data seems more accurate to me. When I go cycling for an hour the Activity App shows me around 350kcal (Active Calories), one hour run is 450kcal. So an activity that is way harder (running) only burns like 100kcal more? My Heart Rate is about 40-50bpm higher on the run.

    I spook to some people on Twitter who have similar issues. I already have my second Apple Watch (had a dent in the first, got AppleCare+) so I'm pretty sure it's not a hardware issue.

    Did Apple do their tests only indoors (ABC Video)? Did they forget to take it outside? :)

    It's probably an issue that they can fix pretty fast. Hope they know about it. Kathy Turlington should tell them.

    Attached Files:

  2. plantoschka thread starter macrumors member

    Apr 23, 2015
    Is it possible to add activity data manually? When I go swimming I want to add this to my activity rings.

    Tried it trough the HealthApp but it doesn't get imported to the Activity App.
  3. TallManNY macrumors 601


    Nov 5, 2007
    The watch does not use your phones GPS to track your run. It uses accelerometer and pace, which is more battery efficient and which will work without you having to take your phone with you. The watch will use GPS to calibrate itself though over time. Do the calibration process a few times and it will become more accurate. But it isn't a GPS watch. And if you run with your phone, you can just use an App on your phone to use GPS to track your run and you can forget about the watch App for anything too specific.

    Or you can leave your phone at home and use the calibrated watch and be pretty close.
  4. plantoschka thread starter macrumors member

    Apr 23, 2015
    Are you sure?

    I thought the Watch will use the iPhone GPS to measure the distance. At least when you take your iPhone with you.

    I thought it will only use the data from accelerometer (and calibration) when you don't take your iPhone with you.
  5. flur macrumors 68020


    Nov 12, 2012
    This is my understanding also.
  6. nullman macrumors newbie

    May 2, 2015
    Hmm, that's not what Apple's site says here:

    GPS. Along with its accelerometer, Apple Watch uses GPS on your iPhone to more accurately measure distance and speed during workouts you do outside — like walking, running, and cycling.
  7. sdallnct2 macrumors regular

    May 3, 2015
    I've been using Nike+ GPS for years on my iPhone. I see similar results using this app on my Watch.

    I'm not entirely sure why the same app would show different results if the only difference is now using the Watch. My understanding on these 3rd party apps is they are simply showing what the app on the phone is doing.
  8. HelloMikee macrumors 6502a


    Jun 16, 2009
    San Diego
    Oddly enough I am seeing similar results. My outdoor runs tend to show much shorter distances and calories burned over a few iPhone apps I've used in the past.

    Similarly odd is when I'm doing an indoor run, the watch is logging in longer distances and faster pace then the treadmill (multiple treadmills used).

    Oddities aside, the watch really does get me off the couch and out for a run or to the gym so I guess that's good lol.
  9. plantoschka thread starter macrumors member

    Apr 23, 2015
    It motivates me too. But more accurate data would be even better :)
  10. SNGR macrumors newbie

    Apr 5, 2015
    I have been experiencing this issue as well. I regularly run with Runtastic Pro on my iPhone 6 Plus and the Apple Watch using the Apple workout app seems to be off by about 10% every run. It seems so weird to me that the Apple workout app shows a different distance as both apps use GPS. Hope they release some kind of fix for this in the future.

    EDIT:I only run outside, haven't tried the other workout options.
  11. TallManNY macrumors 601


    Nov 5, 2007
    Somewhere else in their description Apple goes into more detail. It says something like "we use GPS when you are doing an exercise, like biking, where the accelerometer on your wrist won't work". Also folks have been finding that biking distances match GPS devices perfectly while running distances are not quite precise. We know the Watch uses GPS to calibrate the accelerometer process and that would make the above sentence accurate as well. But the running distances aren't turning out to be perfect. I think that is because the Watch is not using GPS (or at least not accessing GPS as continuously) during runs as compared to bike rides where it isn't getting any feed back from your wrist action.


    I'm not sure. But in another thread a guy was getting perfect GPS match when he went on bike rides and not so good matches when he went on runs.

    This is what I think is happening. On the bike, the watch has no choice but to query the GPS data pretty continuously. During a run (when not trying to calibrate) the watch picks up every step and can gauge your speed by the amount of time between each step. It estimates your stride length from your height and from earlier calibration runs with GPS more information about your stride length. Simple calculations and very battery efficient since the watch is already counting steps all the time. Going back to the phone and asking it continuously "Where am I?" probably would drain the battery.
  12. Wally© macrumors member


    May 2, 2015
    You need to take your iPhone with you for the first couple of rounds...

    Say at least 5...

    The watch will 'learn' from your phone...
  13. dhy8386 macrumors 6502a

    Aug 13, 2008
    The distance reported when doing outdoor activities is still based on accelerometer but Apple says using GPS to calibrate your stride length. More accurate this is, the more accurate accelerometer step count is and hence distanced traveled.

    "Your iPhone GPS allows Apple Watch to achieve even more distance accuracy. For example, if you carry iPhone while using the Workout app workout icon on a run, Apple Watch uses the iPhone GPS to calibrate your stride. Then later, if you’re not carrying iPhone, or if you’re working out where GPS is unavailable (for example, indoors), Apple Watch uses the stored information about your stride to measure distance."
  14. starbot macrumors regular

    Jan 20, 2005
    Indoor data is all based on the accelerometer. They likely have a bit more sophisticated algorithms, but at the end of the day it's calculated by steps taken multiplied by a stride estimated from your height and gender. It's likely to be far less accurate than the treadmill or an outdoor, GPS- tracked activity.

    As has been said, it definitely uses the phone's GPS while outside. The sampling rate is probably somewhat moderate to save battery, thus the distances may not be as accurate, or simply different than apps or devices with quicker sampling rates.

  15. plantoschka thread starter macrumors member

    Apr 23, 2015
    But the accuracy is pretty bad. I mean the accuracy without the iPhone (just Watch, calibrated) seems to be better than with it.
  16. Randizzledante macrumors regular


    May 21, 2011
    For what it's worth, I bring my phone with me, along with the Watch, every time I run, and I swear mine is getting *less* accurate over time.

    I don't even pay attention to the distance stat anymore. Other stats seem fine though.
  17. TallManNY macrumors 601


    Nov 5, 2007
    Do you think the Watch is assuming you ran in a straight line from point A to B each time it samples with the GPS? Could it be losing part of whatever curves or turns there were in your run in between those points?
  18. Break81 macrumors member

    Apr 21, 2015

    same problem here. as well my second watch and still having the problem. Workout by bike works perfect (distance & calories - same results with apple watch and runtastic). outside running; always a gap of 20% in the distance and almost 50% gap in calories counting. annoying...
  19. profets macrumors 601

    Mar 18, 2009
    I don't think it can be added manually. Would be awesome if in future version of the watch we could use it for swimming as well. Are you a triathlete by any chance? ;)

    I thought this as well, based on how they described it. But I've run with the watch + phone many times, and the distance & pace was quite off. Distance several times off by 10% and pace showing me 7:30/km when I'm running between 5:30-6/km. I really don't think it was using GPS even if I was carrying the phone with me. Oddly, several runs with the watch only were much more accurate.

    For cycling it definitely has to be using GPS. Everytime I've used it, it's been spot on.
  20. SpEe1113 macrumors regular


    Apr 24, 2015
    I've thought about this too...I also wonder if the GPS is most accurate when you're running/walking/cycling on paths or streets that are registered on Apple Maps. For example, I live in a fairly new neighborhood of which there are sections not really registered on Maps yet (a jogging path to be more specific) so when I run or walk through that particular area the GPS is kinda just free roaming.

    Remember, the GPS in iPhone does not use a direct GPS satellite like TomTom or Garmin do. It triangulates the signal using cell towers and although it can do so pretty well and pretty accurate, I'm not surprised if it could be off from time to time.

    I'm about 3 runs in with taking my iPhone and my distance seems to be slightly less than I had expected, but I also haven't measured the "exact" distance of my run. I'll give it 2 more tries and then will see how it does without my phone and will verify the specific distance as well.

    I also have a TomTom GPS Cardio watch from before the Apple Watch, I'll plan to wear it on my other wrist for the next run to compare data and will report my findings back.
  21. plantoschka thread starter macrumors member

    Apr 23, 2015
    That's wrong. iPhone (and other Smartphones) can use the GPS Satellites. They additionally can use data from cell towers.

    My theory is that the time interval between two points during a run is too big. The algorithm in the Workout App then probably is a little bit conservative. When I choose Outdoor Cycling the distance is pretty accurate. While cycling it probably has a higher rate of fetching GPS data.

    Don't really know why Apple is doing this like that. Maybe it's to safe some battery life on the phone.
    It's pretty embarrasing that they advertise this product for running (Kathy Turlington) and then provide far less accurate data than it's competitors. The Hardware is there. Apple just have to fix this with an software update. Hopefully they will.

    The accuracy without iPhone trough calibration and the accelerometer is pretty good. But with GPS Enabled it should be way more accurate.
  22. Jayne Doe macrumors member

    Sep 21, 2012

    Got my watch on the 24th. Up till this morning, it's been a inaccurate in a consistent way. (i.e. it says four miles at the same point every time even though Runtastic says it about a tenth of a mile earlier, losing more distance with each mile.) This morning, I go out for a quick four mile run. I expect the watch to say four miles at about the same place as usual. Instead, I go 4.59 miles according to Runtastic and the friend I'm running with). I never reach four miles according to the watch. It thinks I did 3.70 miles. Now that's a sudden HUGE difference.

    This is the quick run around the hood I do almost every morning. Usually, according to the watch, it's about 4.1 miles. Why did it change today? I'm just waiting to see what it pulls out of the hat tomorrow. If this keeps up, time to visit the Genuis Bar.
  23. dhy8386 macrumors 6502a

    Aug 13, 2008
    I think sampling rates, frequency, etc for GPS are irrelevant for outdoor run/walk. If you reread the paragraph above i wrote, the watch is not using GPS to calculate distances. Its simply using it to calculate (or better approximate) your stride length. It keeps amassing this data, which keeps refining how many steps you take with each stride (walk or run). I would actually bet that regardless of choosing outdoor activities or not, its always using the accelerometer which is why results may be varying so much. When I had my fitbit, i would track a mile loop in central park and it would tell me distance of X and then id run the same loop again and that distance would be different, sometimes by a lot.

    For cycling, perhaps they are actually using the GPS, which would make sense.
  24. plantoschka thread starter macrumors member

    Apr 23, 2015
    Maybe it's exactly that.

    Still don't understand why Apple don't just use the GPS on iPhone.
  25. Jayne Doe macrumors member

    Sep 21, 2012
    Maybe this was all part of the Apple Health Master Plan <insert diabolical laughter>

    By giving us incorrect distances, they hope to make us run/bike/walk/jog farther and farther each day by making every mile longer and longer . . .

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