[OSM-talk] Defective GPS trace

[Craig Wallace]

On 01/01/2010 14:14, Steve Bennett wrote:
> On Sat, Jan 2, 2010 at 12:54 AM, Shaun McDonald
> <shaun at shaunmcdonald.me.uk <mailto:shaun at shaunmcdonald.me.uk>> wrote:
>
>     It is very common for GPSs to give errors for whatever reason.
>     Interference is very common from things like buildings. Newer units
>     are less likely to have an issue. You simply need to go along that
>     track again a few times to get an averaged out reading.
>
>
> Well...ok. But in this case I have the aerial photography, so I can just
> trace it, once I know more or less where the path goes. I was just
> curious if there was a way to detect errors at the time - repeating
> every trace several times "just in case" would be pretty inefficient.

You can check the satellite screen on the Garmin. It should show an 
estimated position accuracy.
Also, you can look at which satellites its receiving. If its locked on 
to a reasonable number of satellites in a decent spread across the sky, 
you can be fairly confident in its accuracy.
You don't have any sort of WAAS like system in you part of the world do 
you? That would help a bit.

But I'd still agree with Shaun - a single GPS trace is not really 
accurate enough for adding ways to OSM IMO.
I'd say get at least 2, preferably 1 in each direction. If they are 
close to each other you can be confident its probably accurate. If they 
are much different, its worth getting a few more traces and taking an 
average.

Though yes, this is not really necessary if you have accurate aerial 
photography that you can trace from.

Craig