GPS Overestimates Distance Traveled

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MrBond
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GPS Overestimates Distance Traveled

Postby MrBond » Wed Nov 04, 2015 6:57 am

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turd ferguson
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Re: GPS Overestimates Distance Traveled

Postby turd ferguson » Wed Nov 04, 2015 4:38 pm

The Ranacher team’s results do not mean that measuring the lengths of complex courses by GPS is futile. They point out that moment-by-moment GPS velocity measurement is not subject to the same sources of error, so that calculating distance traveled by integrating velocity should yield reasonably accurate results.


This point is flashing in and out of my understanding. I think its saying that velocity is not subject to interpolation error and so that calculating distance by integrating velocity (which doesn't require distance to be interpolated) is more accurate. But wouldn't the integral of velocity be subject to a different set of errors that potentially make it less accurate?

The best analog I have is to a car odometer. The car doesn't know where you are, it mechanically integrates speed, but if there's an error in the input (like the time I put monster truck tires on my jeep) the odometer is going to be wrong.
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Re: GPS Overestimates Distance Traveled

Postby Jwolf » Wed Nov 04, 2015 5:04 pm

Yeah, I don't get that either.

I also don't really see how it matters that much to runners. It's not that important that we understand perfectly the details of WHY the GPS measures long. It's a combination of factors, and different ones will be more important in some or other situations. The reason most often given- that runners don't run the straightest line measured-- is still a factor, but there are other factors inherent to the nature of GPS measurement as well. This isn't really news. People who use GPS regularly know that the distance it reads will often be long by about 1-2%. That doesn't make it any less of a useful tool as long as you expect this.

ETA: The author comments that maybe runners will be happier to know that the mis-measurement of their marathon is not their fault but the inherent fault of GPS. Maybe, maybe not. It's really only important to know that it's the watch and not the RD's measurement of the course. :)
Races for 2018:
January 28: MEC Race #1 (Stanley Park) 10K- Done!
February 11: First Half Half-Marathon- Done!
March 18: MEC Race #2 (Pacific Spirit Park) 10K - Done!
April 14: MEC Race #3 (Burnaby Lake) 10K Done!
April 22: Vancouver Sun Run 10K Done!
May 6: BMO Half-Marathon - switch to 8K Done!
May 20: Red Deer Half-Marathon -switch to 10K Done!
June 10: MEC Race #4 (Garry Point Park) 10K Done!
July 22: MEC Race #5 (Riverfront Park) 10K or 5K not done
Sept 22: Seawheeze Half-Marathon may cancel this
Sept 30: MEC Race #6 (Garry Point Park) 10K or 5K

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Re: GPS Overestimates Distance Traveled

Postby Commodore665 » Sat Nov 14, 2015 5:23 pm

I've found the GPS is only just out , if I measure the distance in my cars GPS its out by only a k or less , but I think being a slave to them and you tend to enjoy the run less


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Re: GPS Overestimates Distance Traveled

Postby ultraslacker » Sat Nov 14, 2015 6:52 pm

I don't need mine to be perfect (my old one was usually short, not sure about my new one). I use it as a basis for training, but in a race scenario it's just a loose guide and you're going by the race markers and clocks.

Also, I enjoy my runs more with gps than without. :)
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Re: GPS Overestimates Distance Traveled

Postby marymac442 » Sat Nov 14, 2015 10:02 pm

If I run without a gps recording and strava, did it really happen ;)

I don't look at my watch much during a run but I like having the record of accumulated km's.
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Re: GPS Overestimates Distance Traveled

Postby Jwolf » Sun Nov 15, 2015 12:22 am

I think the bottom line is that if you expect the GPS distance to be better than about 1-2% error, then you are "doing it wrong". It doesn't make me feel any better that it's not my lack of running tangents that causes the error. Just expect it to be a bit long - and adjust expectations.

I do feel bad for race directors that get bombarded with emails from runners telling them that the race measured long on their GPS watches.
Races for 2018:
January 28: MEC Race #1 (Stanley Park) 10K- Done!
February 11: First Half Half-Marathon- Done!
March 18: MEC Race #2 (Pacific Spirit Park) 10K - Done!
April 14: MEC Race #3 (Burnaby Lake) 10K Done!
April 22: Vancouver Sun Run 10K Done!
May 6: BMO Half-Marathon - switch to 8K Done!
May 20: Red Deer Half-Marathon -switch to 10K Done!
June 10: MEC Race #4 (Garry Point Park) 10K Done!
July 22: MEC Race #5 (Riverfront Park) 10K or 5K not done
Sept 22: Seawheeze Half-Marathon may cancel this
Sept 30: MEC Race #6 (Garry Point Park) 10K or 5K

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Re: GPS Overestimates Distance Traveled

Postby La » Mon Nov 16, 2015 10:44 am

One look at the map from my run yesterday will explain why GPS watches measure long. My run looks like something a drunk person would have done! :lol:

https://www.strava.com/activities/433471660

In this case, it was interference from tall buildings downtown. And considering many races we do are run in cities, we're going to get some wacky readings.

I'm like Mary: I don't really look at my watch much during my run (just to see how far/long I've gone, and is it time to turn around yet :lol: ), but I like to have the data logged for comparison purposes.

In a race, I'm far more likely to use the KM markers and hit manual lap splits on my watch (along with a pace band) to keep me on pace. That's why I get very cranky if the KM markers are off.
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GPS Overestimates Distance Traveled

Postby Commodore665 » Sun Nov 29, 2015 2:28 am

According to the app I use , this mornings 13.50 Kilometre run took 38 minutes @ 20 kilometres per hour , on my watch it was closer to 1 hour 10 minute


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Re: GPS Overestimates Distance Traveled

Postby Jwolf » Sun Nov 29, 2015 3:14 am

Commodore665 wrote:According to the app I use , this mornings 13.50 Kilometre run took 38 minutes @ 20 kilometres per hour , on my watch it was closer to 1 hour 10 minutes.

That's not normal behaviour for a GPS watch- check your settings. The time should be the elapsed time and shouldn't be shorter.
Races for 2018:
January 28: MEC Race #1 (Stanley Park) 10K- Done!
February 11: First Half Half-Marathon- Done!
March 18: MEC Race #2 (Pacific Spirit Park) 10K - Done!
April 14: MEC Race #3 (Burnaby Lake) 10K Done!
April 22: Vancouver Sun Run 10K Done!
May 6: BMO Half-Marathon - switch to 8K Done!
May 20: Red Deer Half-Marathon -switch to 10K Done!
June 10: MEC Race #4 (Garry Point Park) 10K Done!
July 22: MEC Race #5 (Riverfront Park) 10K or 5K not done
Sept 22: Seawheeze Half-Marathon may cancel this
Sept 30: MEC Race #6 (Garry Point Park) 10K or 5K

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Re: GPS Overestimates Distance Traveled

Postby Commodore665 » Wed Dec 02, 2015 1:33 pm

Jwolf wrote:
Commodore665 wrote:According to the app I use , this mornings 13.50 Kilometre run took 38 minutes @ 20 kilometres per hour , on my watch it was closer to 1 hour 10 minutes.

That's not normal behaviour for a GPS watch- check your settings. The time should be the elapsed time and shouldn't be shorter.


No , it's more" map my run " being a useless app


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Re: GPS Overestimates Distance Traveled

Postby Jwolf » Wed Dec 02, 2015 9:53 pm

Commodore665 wrote:
Jwolf wrote:
Commodore665 wrote:According to the app I use , this mornings 13.50 Kilometre run took 38 minutes @ 20 kilometres per hour , on my watch it was closer to 1 hour 10 minutes.

That's not normal behaviour for a GPS watch- check your settings. The time should be the elapsed time and shouldn't be shorter.


No , it's more" map my run " being a useless app


Actually, the app is pretty useful and I know quite a few people who use it. It may be off a bit in distance, but at the very least it should have the total time of your workout correct. Make sure that "autopause" is off in the settings.
Races for 2018:
January 28: MEC Race #1 (Stanley Park) 10K- Done!
February 11: First Half Half-Marathon- Done!
March 18: MEC Race #2 (Pacific Spirit Park) 10K - Done!
April 14: MEC Race #3 (Burnaby Lake) 10K Done!
April 22: Vancouver Sun Run 10K Done!
May 6: BMO Half-Marathon - switch to 8K Done!
May 20: Red Deer Half-Marathon -switch to 10K Done!
June 10: MEC Race #4 (Garry Point Park) 10K Done!
July 22: MEC Race #5 (Riverfront Park) 10K or 5K not done
Sept 22: Seawheeze Half-Marathon may cancel this
Sept 30: MEC Race #6 (Garry Point Park) 10K or 5K

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Re: GPS Overestimates Distance Traveled

Postby turd ferguson » Thu Dec 03, 2015 11:37 am

Jwolf wrote:
Commodore665 wrote:
Jwolf wrote:
Commodore665 wrote:According to the app I use , this mornings 13.50 Kilometre run took 38 minutes @ 20 kilometres per hour , on my watch it was closer to 1 hour 10 minutes.

That's not normal behaviour for a GPS watch- check your settings. The time should be the elapsed time and shouldn't be shorter.


No , it's more" map my run " being a useless app


Actually, the app is pretty useful and I know quite a few people who use it. It may be off a bit in distance, but at the very least it should have the total time of your workout correct. Make sure that "autopause" is off in the settings.


That is kind of the definition of useless, unless all you wanted was a stopwatch.
"Human beings, who are almost unique in having the ability to learn from the experience of others, are also remarkable for their apparent disinclination to do so." - Douglas Adams

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GPS Overestimates Distance Traveled

Postby Jwolf » Thu Dec 03, 2015 11:43 am

turd ferguson wrote:
Jwolf wrote:
Commodore665 wrote:
Jwolf wrote:
Commodore665 wrote:According to the app I use , this mornings 13.50 Kilometre run took 38 minutes @ 20 kilometres per hour , on my watch it was closer to 1 hour 10 minutes.

That's not normal behaviour for a GPS watch- check your settings. The time should be the elapsed time and shouldn't be shorter.


No , it's more" map my run " being a useless app


Actually, the app is pretty useful and I know quite a few people who use it. It may be off a bit in distance, but at the very least it should have the total time of your workout correct. Make sure that "autopause" is off in the settings.


That is kind of the definition of useless, unless all you wanted was a stopwatch.


My point is it's not useless in general but he's got the settings messed up.

If the app is just off slightly in distance (the app may be out a little more than the 1-2% of the GPS watch) it will still be very useful for tracking your distance. And many people do that. In the big picture it's not going to make a huge difference if you log 13.1 or 13.5K as long as you have consistency.

He's calling the app useless because his total time was off - that's an easy fix.
Races for 2018:
January 28: MEC Race #1 (Stanley Park) 10K- Done!
February 11: First Half Half-Marathon- Done!
March 18: MEC Race #2 (Pacific Spirit Park) 10K - Done!
April 14: MEC Race #3 (Burnaby Lake) 10K Done!
April 22: Vancouver Sun Run 10K Done!
May 6: BMO Half-Marathon - switch to 8K Done!
May 20: Red Deer Half-Marathon -switch to 10K Done!
June 10: MEC Race #4 (Garry Point Park) 10K Done!
July 22: MEC Race #5 (Riverfront Park) 10K or 5K not done
Sept 22: Seawheeze Half-Marathon may cancel this
Sept 30: MEC Race #6 (Garry Point Park) 10K or 5K

Commodore665
Percy Williams
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Re: GPS Overestimates Distance Traveled

Postby Commodore665 » Fri Oct 28, 2016 4:26 pm

Jwolf wrote:
turd ferguson wrote:
Jwolf wrote:
Commodore665 wrote:
Jwolf wrote:
Commodore665 wrote:According to the app I use , this mornings 13.50 Kilometre run took 38 minutes @ 20 kilometres per hour , on my watch it was closer to 1 hour 10 minutes.

That's not normal behaviour for a GPS watch- check your settings. The time should be the elapsed time and shouldn't be shorter.


No , it's more" map my run " being a useless app


Actually, the app is pretty useful and I know quite a few people who use it. It may be off a bit in distance, but at the very least it should have the total time of your workout correct. Make sure that "autopause" is off in the settings.


That is kind of the definition of useless, unless all you wanted was a stopwatch.


My point is it's not useless in general but he's got the settings messed up.

If the app is just off slightly in distance (the app may be out a little more than the 1-2% of the GPS watch) it will still be very useful for tracking your distance. And many people do that. In the big picture it's not going to make a huge difference if you log 13.1 or 13.5K as long as you have consistency.

He's calling the app useless because his total time was off - that's an easy fix.


No not all , you would enjoy running more if you ditched it like I did


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