iPhone vs Garmin GPS Distances!

[GeorgeAndDiana]

Now get ready for all the posts on Jan 9 about the course being LONG. It is not. A GPS unit will measure long due to the fact you, the runner, are not running the shortest path on the course.

Yup. I've noticed that courses I've run have been "longer" than the Garmin measured, and that was just a 10K.. so, I was definitely a little interested/concerned that the iPhone+RunKeeper was giving me even longer distances than the Garmin. I'm okay with the margin of error.. I just want to know approximately what margin to expect.

 

[hungrygreenhippo]

They both have different sampling intervals and smoothingnalgorithms. I wouldn't be surprised if ruNkeeper was actually lining you up with roads rather than just tracking points which would eliminate some if what gamins see when you zigzag and don't run perfect tangents

I run with my iPhone and use 2 apps - RunKeeper and Runtastic. The reason for this is in case I have an issue with one app that the other is hopefully still tracking my time and distance, which has happened before. Even though it's the same device I get different distances on each app, off by .1-.2 miles. Is this probably because of the sampling intervals and smoothing algorithms as Matt suggested? I turn start both apps before I start running so that's not an issue.

 

[cewait]

I run with my iPhone and use 2 apps - RunKeeper and Runtastic. The reason for this is in case I have an issue with one app that the other is hopefully still tracking my time and distance, which has happened before. Even though it's the same device I get different distances on each app, off by .1-.2 miles. Is this probably because of the sampling intervals and smoothing algorithms as Matt suggested? I turn start both apps before I start running so that's not an issue.

I would say yes, the software behind the apps can use different algorithms as well as one my use cell data exclusively.

One other phone vs GPS issue is that an iPhone will change between cell tower and satellite transmitters depending on signal strength and what will keep the phone working faster. That is faster and not accurately.