Here's the maps produced by both solutions:
In order to test the accuracy of both devices I reset them before my drive home. However, both measured the exact same distance by the time I arrived at my house. I suspect the problem is related to losing the signal while on the trail in the trees. But I am not sure how to test them to figure out which one is actually more accurate. Is the Garmin showing a shorter distance because it is missing some of the distances on switchbacks, etc. Or is the AllSport getting confused and adding miles to guesstimate distances after it drops and reconnects?
When I zoom in on the maps of both devices I can see that the AllSport tracking isn't as accurate in some locations. For example, I can see it crossing over parts of the trail that I know didn't cross over (see picture below). These areas could add to the distance. However, when I zoom in on the Garmin, the tracking seems to be much more representative of the trail, but there are fewer data points.
So I think possibly the Garmin is showing a shorter distance because it isn't plotting as many data points and might miss some of the distance on switchbacks or other tight turns--or it's simply more accurate than the AllSport GPS software. I think I remember a setting on the Garmin that can increase the number of data points. I will change the settings to see if I get different results.
If anyone has a suggestion on how to determine which is more accurate, or on how to dial-in these devices so they are more accurate, please leave me a comment. Thanks in advance.
Note: Three days after writing this, I solved the accuracy mystery.
Check out this link:
ReplyDeletehttp://www.irunfar.com/2010/08/tips-for-gps-improving-accuracy-when-running.html
Hope it helps!
I know one issue with any GPS unit and tracking data points is speed. Assume that two runners use the same GPS device and run the exact same route that has a lot of twists and turns. The faster runner will have fewer data points over the entire route because his time will be shorter. The slower runner will have more data points because he's on the course longer. Thus, the slower runner would have a more accurate picture of the actual route. There's another runner out there that has explained this much better than me but I can't find the link. I hope I explained it well enough, but it does present some interesting questions about GPS devices.
ReplyDeleteThe switchbacks kill the accuracy on a GPS watch. I use a 405. I just ran a 50K here in MS, and lost almost 4 miles over the course of the race. The trees play a factor in accuracy too. My last race was 5 6-mile laps (and a bonus mile to make the 50k) on single track and to see it on the Garmin you would never know that. I am training for a 50-miler, so I am more concerned about time on my feet as opposed to mileage. Sure, it is fun to have the stats and see your accomplishments, but mileage is not something to get super hung up on in ultra training. I have also been testing the Adidas Micoach and have been floored about how accurate it has been compared to my Garmin on an open clear road. It was less than .35 off over 20 miles a couple weeks ago straight out of the box. Good luck in your training.
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