Originally Posted by
mschwett
i definitely get much cleaner results than that with my iPhone; i can't really find any in the last 20 or 30 rides that are grossly off except for going through tunnels. perhaps the iPhones augmented GPS is doing something, perhaps it's just luck. i've chalked up major differences (more than .5%) in rides to tire inflation changing the accuracy of the wheel sensor, and the GPS always being just a tiny bit short of the real distance thanks to the straight-line-interpolation.
I think I generally get better results. I think part of the issue was because I was going fairly slowly. I was mostly seeing what the sampling rate was.
iPhones might be a bit weird.
http://regex.info/blog/2015-12-03/2651
http://regex.info/blog/2016-01-19/2666
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The purpose of the "assisted" part of the "assisted GPS" is to get a location when there is no GPS signal (like indoors) or to "warm up" the GPS.
It also provides a location quickly (much faster than GPS on startup). For many things, the phone cares that it's quick not very accurate.
It takes a while for GPS to stabilize and the more accurate the initial estimate for location, the faster it can stabilize. Once it's stabilized, GPS is very fast and much more accurate than other methods.