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Re: [RC] GPS Accuracy - AprJhn

The GPS should be marking your position every x number of seconds (or feet if your GPS will do that). Replace x with a reasonable number for your terrain (ie, switchbacks, hills), I like 5 seconds. With mine I can set that. As long as your GPS is picking up all your switchbacks (the reason to mark every 5 seconds or so), the linear distance will be pretty close to your actual distance. Within hundreths of a mile. Not tenths, not miles. Hundredths of a mile.

I have a topo map program that I use to measure distances and it will measure linear distance and terrain distance. Surprisingly, not much difference. There are mathematical formulas to prove this. Might be some in the archives. I've just accepted it and moved on. But 12 miles on my hillly trails seem much longer than 12 miles on my flatter track. But they're still both 12 miles.

A much more prevalent reason for miscalculated distance is loss of satellite reception. If the GPS can't see the birds, it doesn't know where you are and will lose accuracy.

You can get more accurate GPS equipment than the handhelds, but they're bulky, expensive, and hard to get ahold of. :)

As for using GPS receivers to map out an endurance ride, that's a whole different topic.

April
Nashville, TN


Laurie Durgin wrote:


I remember the discussion a while ago about distance inacuracies if you have a lot of hills, (mountains, canyons for example)Someone said it marked the Grand Canyon alot shorter than it was? Had to do with Linear distance.satilittes.Orginally created for ships?
Makes me wonder afte doing the Talladeaga, Al. ride. They GPS ed it for the distance, but there were people there saying it didn't feel right. It felt longer to me too. And that is a hilly, winding ride. Makes you think. ..





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Replies
Re: [RC] [RC] Timex GPS, Laurie Durgin