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

[Nick Allen]

Hi

I'd second the comments from Mike. 

I mainly survey by cycle & foot. I also take into account the weather in
my 'guestimate' - if it is cloudy my GPS signal tends not to be as
accurate as on a bright sunny day. My traces in trees or tall buildings
can wander all over the place. But in any case even on bright days in
the open, there is always some difference in my traces.

Potlatch is handy if others are likely to have submitted traces of the
area you are mapping.

Regards

Nick
(Tallguy)

On Sat, 2009-01-17 at 10:28 +0000, Mike Harris wrote:
> 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
> 
> 
> 
> 
> 
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