So what the heck happened to the Garmin GPSMap60CSx–it was off by nearly 10%?! There’s another factor at play here, and it’s known as polling frequency. Still, having more sensors available to calculate location isn’t a guarantee of accuracy–the Garmin Fit app on an iPhone 5 ended up middle of the pack in our distance test, and the Nokia Lumia smartphone ranked 8 out of 10. And the Magellan Cyclo505–#4 above–is also wi-fi enabled, though we don’t know if it’s actually using wi-fi to improve location accuracy. Two of the top four GPS units in our distance accuracy test are regular old smartphones that determine location not just with GPS but also using wi-fi and cell tower signals to triangulate a position. Product engineers know the device isn’t completely accurate so why not just estimate everything on the high side to keep riders happy? □īut let’s stick with the idea that chipsets affect distance accuracy for a moment. In my own experience I’ve noticed most GPS units report distance on the high side (for example, clocking 104 miles in a 100-mile race), and perhaps it’s by design to make consumers feel faster/stronger than they really are. Surprisingly, all but one of the devices over-reported the distance, which either means our track is slightly longer than we assumed or something else is going on. On average (if we throw out the Garmin 60CSx) each device is off by about 1.4%, which is probably a good number to assume whenever analyzing your own data. Still, only 4 out of 10 were within 1% of the actual distance. Overall, the error rate is pretty low–around 3% or less for all but one device. Keep this in mind when using GPS to map trails. Interesting to note that the most accurate in terms of distance are not necessarily the most accurate at plotting route data. Top 5: Asus Nexus Tablet (Strava), Nokia Lumia (GPS Logger), Garmin Fenix2, Magellan Cyclo505, and Garmin Forerunner 405.īottom 5: Garmin GPSMap60CSx, iPhone 5 (Strava), Garmin Edge 500, iPhone 5 (Garmin Fit), and Garmin VIRB Elite. Subjectively, here’s how I would rank the accuracy based on the route plot: The actual route hugged the inside lane for each lap, though you can see some of the data veers toward the inside of the field and the edges in some cases ( click here for an interactive plot). Looking at the animated graphic at the top of this article, you can get a sense for another measure of accuracy–basically the tightness and “correctness” of the ride data. Here are the results, ordered by distance accuracy. We didn’t test timing on the devices since each unit is designed to sync time with the GPS satellites themselves, which meant we wouldn’t need to start and stop all devices at the same time. I stuck to the middle of lane 1 (thanks for the velodrome tip Chris!) and each GPS was started (but not moved) one at a time. All were rigged to a single rider (me!) and the test started and stopped at the same point on the track after riding 10 laps (2.5 miles). We did our best to mount each unit according to its normal configuration that is, wristwatches on a wrist, bar-mounted units on the bars, etc. To find out, ckdake and I took 10 GPS devices–including 2 wristwatches, 2 bar-mounted units, 3 smartphones, 1 GPS-equipped helmet camera, 1 handheld device, and even a tablet–to a local quarter-mile track to see how each performed. Still, I was curious: was there any difference in accuracy between various types of GPS devices? I’ve personally been biking with a GPS since 2001 (13 years!) and my take was that neither is any more or less accurate than the other. Over the summer there was an interesting discussion in the comments section of this article about the accuracy of dedicated GPS units from companies like Garmin compared to the GPS data collected via smartphones.
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