thalia: woman running, caption "Thalia" (running)
Thalia ([personal profile] thalia) wrote in [community profile] runners2017-05-30 12:38 pm

Tangents

Last weekend [personal profile] meri_oddities and I ran the Green Bay half marathon, and it was really fun. Very well-organized race. I was totally untrained, though, so we're not talking about my time.

I was using my iPhone for race tracking, and it says I ran 14.26 miles, rather than the expected 13.1. What I'm trying to figure out is, is it possible that my tangents are that horrible, or is the phone probably wrong? I've never had reason to think its distance is inaccurate before; I use it all the time running at home, and its distances have always been more or less the same as what I'd get from my Garmin on my regular routes. But, wow, that's a big difference.

Here's the mile-by-mile breakdown. I missed the first mile marker, so the first lap covers the first two miles.
Mile Marker Race Distance GPS Distance
2 2 2.08
3 1 1.03
4 1 1.03
5 1 1.11
6 1 1.13
7 1 1.1
8 1 1.09
9 1 1.05
10 1 1.04
11 1 1.07
12 1 1.08
13.1 1.1 1.45
Total 13.1 14.26


That last lap included a foray into Lambeau Field, and I stopped a few times for photos, so I'm not surprised it's on the long side. Most of the other laps aren't too awful, except for miles 5 and 6.

What do you think? Do I just need to learn to run better routes? Are my phone's numbers completely unlikely? Help!!!
ilanarama: me, The Other Half, Moab UT 2009 (Default)

[personal profile] ilanarama 2017-05-30 08:46 pm (UTC)(link)
It's probably a combination of failure to run tangents (I see the course makes a lot of turns) and GPS errors, which are partly due to the phone chip and partly due to satellite uncertainty. Are there a lot of big buildings on the route? That can add to the misreadings from the GPS.

I just did a search on Strava which came up with a bunch of hits for Green Bay half marathon (over several years) and you can see that the apparent distance ranges from 13.0 (!) to 13.8 (not counting a 20.6 which looks like the guy forgot to turn off his Garmin when he got in his car to leave!). Yours is pretty far off, but not ridiculously (except for the last 1.1, which seems awful).

I don't know how old your iPhone is, but I can tell you that when I went from the Garmin 301 to the 305, and from the 305 to the 610, my race distances got closer to nominal. A fairly straight half with the oldest watch came in at 13.34, same one with the newest was 13.17. So it does make a difference.
linaelyn: (exercise running by dropsofsunshine)

[personal profile] linaelyn 2017-05-31 05:39 am (UTC)(link)
Tunnels do indeed play havoc with iPhone GPS, as evidenced by my ability to spin Pokéstops (in Pokémon Go) that are up to a mile away, while driving through tunnels. (ONLY when I'm a passenger!)

As much as I'd LIKE (as an Apple Spouse, whose bread & butter comes from the company) to say the GPS on the iPhone is every bit as good as a Garmin... um... yeah. Not so much. Wearing a (2nd generation! yes, it matters) Apple Watch and ALSO using the iPhone on one's person, definitely improves the odds for being geolocated accurately.

Distance is one of the things that Apple is still working to get right. But, at least there was a recent study that showed they are best in the class, for caloric burn data and heart rate monitoring? I have a friend who had her fFitBit tell her she had a serious heart issue, and careful doctor's monitoring showed nothing. Dr.'s prescription was to borrow an apple watch for a month and see if the problem reappeared. It didn't, so she was declared the victim of tech glitch in the FitBit. :-}
linaelyn: (hugs from kittens)

[personal profile] linaelyn 2017-05-31 05:43 am (UTC)(link)
Additionally, GO YOU!!! I want to try a couple of half-marathons around here, or at least some 10k races, before summer is over. But... I haven't been training, trying to totally heal up that plantar fasciitis. I'm walking 10 miles a day right now, and running maybe 5K on a regular basis. It's nice to see you are not afraid of running a race when you haven't trained! Well done!!! <3
linaelyn: (Lin as Chibi!Pirate - art by _audrey)

[personal profile] linaelyn 2017-05-31 05:46 am (UTC)(link)
Oh! You have the 7? I am on the 6, which might be different. In either direction, truth be told. So take my comment with a grain of salt.
camper4lyfe: (Default)

[personal profile] camper4lyfe 2017-07-12 02:42 pm (UTC)(link)
I know I'm late on this, and I'm new to the community, but I wanted to chime in a bit.

Phone GPS is notoriously inaccurate compared to a GPS watch, which is notoriously inaccurate when compared to actual measured distances due to the nature of how it all works.

The combination of the phone GPS inaccuracy and most likely not hitting the tangents properly (as ilinarama pointed out) combined to giving you a much hither distance.