[talk-au] Hi all ...

[Delta Foxtrot]

--- On Wed, 17/6/09, Ross Scanlon <info at 4x4falcon.com> wrote:
> I guess it comes down to 99% of the ways I've mapped I've
> been the first
> one there.

This is why you should upload your GPX files, because even if you are the only one to map out a location, that isn't to say that will always be the case. Once there is enough traces ways can be shifted to the average location and the map ends up more accurate as a result.

> Yes but how many places have you seen with 50 traces there.

Not many, then again I'm not looking at GPS traces for metro areas, I can only assume either people probably just trace out their info and not bother uploading them or there isn't any traces available at all.

> Additionally if you are tracing the gps trace and not using the nodes
> from the gps trace then you are introducing another error.  It's rare
> that these traces are more than 5m apart anyway and most of that is
> operator induced eg overtaking another vehicle, going arround a pothole
> in the road.

There is all sorts of reason there can be error besides mistakes operating your equipment or how you drive round pot holes.

* You can be in an urban canyon or any other area that will increase multi-path interference, or reduce your view of the sky.

* You can have just bad timing and not have many satellites over head and on top of that the ones you are seeing are close together.

* There can be freaky things going on in the ionosphere and you won't even know about that one unless you compare against other results, or have a device that operates on dual frequencies.

To name a few of them, more obvious ones are being in a tunnel, although mobile phones with A-GPS can get round this.

> But as my first post said don't change anything that is tagged as
> source=survey unless you have a really good reason, eg road has been
> moved.

Or the original trace wasn't done accurately in the first place, either due to GPS errors, operator related or otherwise, or they didn't plot out the trace matching the GPS points, or even a software bug could be at fault.

The reasons for errors in any system can be varied.