[talk-au] Hi all ...

[Ross Scanlon]

>
> --- 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.

No, it's not why I should upload the GPX files.  As I said the info I
upload from josm is the edited version of the gpx files I don't move the
nodes just use josm's simplify tool to remove all unnecessary nodes.

> 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.
>
> The reasons for errors in any system can be varied.

No kidding, do you really think that we don't know this.  I've been using
GPS since 1993 so I've got a pretty good idea of possible errors with
them.

>> 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.

As I said if you have a really good reason to change a source=survey then
do so but don't change it just because it's your trace and you think yours
is the only correct one.  Leave it alone if your not sure.

Averaging the traces will not necessarily make the map more accurate.  If
there are two that correspond closely and one that's 20m off then the
resultant way will be incorrect.



-- 
Cheers
Ross