[OSM-newbies] new to OSM editing - advice on coping with gpx /POTLATCH offset

[Mike Harris]

Hi!

Personally, I wouldn't trust the gps signal (even with WAAS corrections) to
better than 5-10 metres. I have tried walking the same route several times
and this confirms the level of consistency. As a walker-mapper I often find
it necessary to do a little interpretation. I tend to adjust an OSM feature
where it seems sensible to do so. Many existing OSM traces have been done by
cyclists (or even from a car on major highways) so a walker's record is
likely to be more accurate. Nevertheless I never adjust by more than a few
metres and at the most to half way between the original OSM position and the
gps trace. If I walk the route again later I apply the same sort of rule -
so there is a process of successive approximation! Of course, if I know from
surveying that the existing OSM trace is seriously in error I would then
make a correction and, if appropriate, added a note= to say what I have done
and why.

Hope this is a sensible approach!


Mike Harris

-----Original Message-----
From: JW [mailto:jameswillmer at googlemail.com] 
Sent: 15 January 2009 00:48
To: newbies at openstreetmap.org
Subject: [OSM-newbies] new to OSM editing - advice on coping with gpx
/POTLATCH offset

Hi all

I started small by adding some .gpx data (Blackberry curve / bbtracker.org
app)
to local maps in areas which i know well.    
This area has been mapped
previously by someone using potlatch and the yahoo available satellite
photos (UK)

It turns out that there seems to be an
offset between potlatch  locations and
.gpx data i record - maybe 5 to 10m or so.


There are a few courses of action

1) trust my phone gps .gpx data is correct 
and change all potlatch locations as
i can..... this is not practical for 
a small edit added to a large mapped area

2) don't worry about it this is 
within normal gps errors ..... just "interpret"
where the footpath is and add it beside the potlatch road.

3) something else?

What do others do?

Ciao
JW