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:[email protected]] Sent: 15 January 2009 00:48 To: [email protected] 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 _______________________________________________ newbies mailing list [email protected] http://lists.openstreetmap.org/listinfo/newbies
