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September 15, 2012

Which do you believe, the map or the GPS?

If you read my last grumpiness regarding Nike+, you probably know that the answer to the above question is, “It depends.”

It turns out Strava has the same problem as Nike+ when it comes to using the GPS in the iPhone to track runs. Simply put, both apps trust that the GPS track from the phone is 100% reliable; once a run has been tracked, there is no option to correct the track or replace it with something generated from a map.

This would be wonderful if the GPS track was, in fact, 100% reliable. But for some reason in the last few weeks, my GPS tracks have been consistently bad. I’ve had seven-mile runs marked as two and a half, two-and-a-half mile runs marked as three… it goes on and on. I don’t know if the problem is the phone hardware, the apps, local topography, local weather, solar weather, or some combination, but it’s pretty consistently bad.

And it highlights the problem with using GPS tracks to get run distance (or much other run data): GPS as a technology is much more precise than it is accurate. Put another way, like email, GPS is a “best effort” technology (much like email). It can be wrong, and if it’s wrong it will not apologize nor necessarily admit the error.

So why don’t either of these logging systems accept an alternative? All they need is an option—it can be on the website, it doesn’t need to be right in the phone app—to indicate for a given run if the GPS track is actually correct. The user could have the option to upload a .gpx file with a better map track if they want to generate one with another app. (It’s hypothetically possible to use the Gmap-pedometer to create a gpx file, and use that to record a new run with Strava, but so far the gpx files I’ve tried uploading to Strava have failed.)

Introducing this option of human oversight is a simple way of accounting for GPS’s lack of accuracy. I’m sure most of the app developers want to avoid that degree of complication, but in doing so, they’re placing more trust in a fallible technology than it really deserves.

ETA: So the issue with my GPS inaccuracy turned out to be the iPhone and not the apps. Still, how do I correct the logs?

Posted by pjm at 1:40 PM | Comments (0)

September 7, 2012

Data portability

For the last year, I’ve been using the Nike+ running iPhone app to log my running. This was somewhat against my better judgement, as I tend to worry about consigning my data to warehouses out on the ‘net without some means to keep a copy in my own control, but I started when the girls were infants, and I needed something shiny to keep me motivated to get out the door on a regular basis. I have also become terrible at keeping up my paper logs (much like this weblog) and something which would automatically record my data sounded like a good idea.

However, a phone app has its pitfalls. I ran into two cases in the last few weeks which led to messy data in the log:

  • During a run, I “paused” the app, but then inadvertently “finished” the run (a different tap). I had to start a new one to track the rest of the run. Not only were my numbers a little goofy, but Nike recorded this as a double workout.

  • More recently, running on Battle Road I had a sketchy GPS signal. As a result, the hour-and-a-quarter run was logged as two and a half miles rather than seven and a half, warping the data quite significantly.

Both of these things should be pretty easy to fix given a little data tweaking, but it turns out Nike doesn’t support such things. What comes from the phone is considered Truth. I contacted tech support asking how I could fix these runs, and their answer was to delete the runs from my activity and email them the details of the actual runs to be re-inserted in my record.

Needless to say, this seems like a cumbersome approach.

So I’m shopping for a better logging solution. At the moment, I’m looking at Strava which comes well-recommended. But first I need to liberate my data from Nike+ (sound familiar?), and it looks like even that is problematic. I wonder if this shouldn’t be a standard part of how people evaluate online services: “How hard will it be to download everything I upload to this site?”

Posted by pjm at 7:00 PM | Comments (0)