Author Topic: GPS accuracy controversy  (Read 1312 times)

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Offline mdxix

GPS accuracy controversy
« on: December 22, 2011, 12:01:56 am »
Many are picking up on NYT article about unreliable GPS receivers:
http://www.nytimes.com/2011/12/20/health/nutrition/gps-watches-may-not-track-runs-accurately.html

The AMC is not surprised:
http://equipped.outdoors.org/2011/12/how-accurate-is-gps-watch.html

Ray Maker strongly disagrees:
http://www.dcrainmaker.com/2011/12/why-new-york-times-gps-running-article.html

The author of the article, Ms Kolata, does not say where the route was, the density of trees, the surrounding high rises of NYC, or weather conditions. These can cause major distraction to the GPS signal.

I use the Edge 705 on my bicycle. The altimeter is more random than the stock market. But the distance has very small error. For example, here are a few rides I charted and recorded:

122.28km GPS vs 123.7km map (98.9%)
76.6km GPS vs 76.8km map (99.7%)
113.2km GPS vs 111.5km map (101.5%)
36.8km GPS vs 36.9km map (99.7%)

This works for me.

Offline Fred Hiltz

Re: GPS accuracy controversy
« Reply #1 on: December 22, 2011, 07:58:57 am »
Thanks for the references. Those articles are interesting, more for the psychology than the technology. As GPS has spread from the enthusiasts to the general public, false expectations are inevitable. The early adopters who learned about the technology and its limitations would not be surprised.

I'll add another confounding phenomenon: "rogue" positions due to reflections of the signals, most common in canyons--urban or natural--but can happen anywhere. The poor position of a wrist watch, shielded by the wearer's body from many of the GPS satellites, does not help. When I map the track points made during a ride or a hike, occasional single points will appear dozens or hundreds of feet off track. They add considerable distance to the GPS reading, but are easy to delete on a computer. Some of the reported high readings are probably due to rogue positions.

Fred

Offline whittierider

Re: GPS accuracy controversy
« Reply #2 on: December 22, 2011, 04:41:39 pm »
One of our customers sent us his hand-held GPS--not even a watch-type--to get help making it work with our product (for aircraft) which he had bought.  The GPS had us halfway down the next block.

Offline waynemyer

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Re: GPS accuracy controversy
« Reply #3 on: December 28, 2011, 07:06:33 pm »
The early adopters who learned about the technology and its limitations would not be surprised.
Yep. Sometimes the GPSr can tell if I am on the shoulder or riding in the right-hand tire track. And other times my accuracy (according to the unit) is >75 feet. Meh; it is what it is.
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