- Time of past OR future Camino
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At least 2 - 3 times a week, I read a post where someone complains that the guidebook s/he’s using (Brierley is most often singled out for the blame) understates the distance actually walked, as measured by the poster’s supposedly reliable gps. And in fact, since my wife started carrying a gps measuring device several caminos ago, we’ve noticed the same thing — that the guidebook, app. or website we’re using generally understates the gps distance by 5 - 10%.
BUT (we’ve also noticed), it doesn’t matter what guidebook or app we’re using — Brierley, Wise Pilgrim, Gronze, Whitson, CSJ, or others in different countries — and it also doesn't matter which of several gps devices my wife is carrying. The gps distance is always greater than the distance stated in the guidebook or app.
So can all the different guidebooks be wrong, and all the different gps devices be right?
The answer, obviously, is “no,” and if you do a simple google search for “Accuracy of GPS distance measurements,” you’ll find a ton of information, including from gps manufacturers like Garmin, which all acknowledges that gps measurements always overstate diistance by a factor of 5% or more because of the limitations of the technology. As I understand it, the reason is that gps devices measure distances not in the continuous line you are walking, but from various fixed points, all of which are several meters or more away from the actual point you are walking, so when all the gps dots are connected up, the total distance shown will be greater than the distance you actually walked (kind of like measuring the legs of the triangle instead of the hypotenuse). Here’s a good, clear article that explains it: http://cincyhalfmarathon.com/GPS Accuracy.pdf
So what’s the lesson here? Put your phone down, and walk! You’re going to get there when you get there. Easy to say, I know.
BUT (we’ve also noticed), it doesn’t matter what guidebook or app we’re using — Brierley, Wise Pilgrim, Gronze, Whitson, CSJ, or others in different countries — and it also doesn't matter which of several gps devices my wife is carrying. The gps distance is always greater than the distance stated in the guidebook or app.
So can all the different guidebooks be wrong, and all the different gps devices be right?
The answer, obviously, is “no,” and if you do a simple google search for “Accuracy of GPS distance measurements,” you’ll find a ton of information, including from gps manufacturers like Garmin, which all acknowledges that gps measurements always overstate diistance by a factor of 5% or more because of the limitations of the technology. As I understand it, the reason is that gps devices measure distances not in the continuous line you are walking, but from various fixed points, all of which are several meters or more away from the actual point you are walking, so when all the gps dots are connected up, the total distance shown will be greater than the distance you actually walked (kind of like measuring the legs of the triangle instead of the hypotenuse). Here’s a good, clear article that explains it: http://cincyhalfmarathon.com/GPS Accuracy.pdf
So what’s the lesson here? Put your phone down, and walk! You’re going to get there when you get there. Easy to say, I know.
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