Accuracy is indeed a problem.
An early OSM update I made was moving a borderline by 250m and put a devotion site from an arrondissement to another.
Since then many corrections of more that 5 m, mainly due to user being unaware of Bing's offset (at close zoom of course, in some places only, poisoned gift) and some editors.
I just checked a place where I had spotted a Bing offset before.  National aerial photos 2009 and 2012 were offset by 2.8m. Bing was almost in the middle
Smart phones have a bad accuracy reputation. I have however bought one based on a "good GPS" user report and, indeed I verified quick fix and immediate 4m accuracy by cloudy weather in a veranda. Former one around 10m and couldn't fix in house.

On 2014-12-23 18:49, Malcolm Herring wrote :
On 23/12/2014 16:57, Tom Pfeifer wrote:
The collection of
   traces over a longer time creates a cloud of traces which
   form a Gaussian bell curve, in density, over the ground truth.

Except that the position of a node in the DB is the last edited value, not the mean position of all historical values.
Yet, I sketched a funny program that analyzes a GPX trace, determines when the car stops (I doubt it could work for foot), takes the mean value of the wandering position until the car moves again, and creates a POI for JOSM to layer.
The results were surprising for an alpha 0 pre-release pure hack.  After rolling up one's sleeves higher, one could imagine processing several traces, such as ones recorded by buses to determine the coordinates of the stops.
I had been surprised by how much the GPX position moves about when the GPS is stopped (compared to when it moves) and I will test that with my new smartphone when better weather returns.

Cheers

André.


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