Sometimes, while editing I notice that other lines people have drawn are “off course.” This presents a chance for me to ask a few questions about this and probably learn something I didn’t know before.
1/are these errors most likely caused by human error- basically be “hastily drawn incorrect lines”?
some of them seem very far out from the actual road.
2/ I know a little about GPS coordinates being altered due to “space/time” movement. Is this anything to do with it?
3/ if a line is badly drawn and you are driving along the road, what’s the maximum distance that the GPS could read the line before being unable to read the route? Thanks I would be interested to know what’s going on.
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I’m sure that lots of people would be able to add lots more detail here, but just to start the answers off:
- Yes, that can happen. The “level of detail recorded” (whether from a GPS trace or from e.g. imagery) is often less than perhaps we’d like. Someone might draw a quick “first draft” so that other people can tidy up later, and that’s perfectly OK - OSM has always improved that way.
- Yes, if I record a GPS trace today, tomorrow and next week, I might get different traces. That’s why aggregate GPS data (such as OSM’s GPS layer, or Strava’s) are so useful.
- It depends on the GPS hardware. My experience based on many years experience is Garmin hardware is that it’s surprisingly large - maybe 50m or so. Often GPS devices have some sort of “snap to road” features - they may show you at “their best guess on a planned route” but are actually recording your position as slightly different. I can’t generalise though, as every manufacturer and device is different.
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Could have also been the join between 2 sets of imagery, taken at different dates, with the old set at the right being way off, while the newer set was good?
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Or maybe the first mapper who put this track on the map had only bad quality imagery available. A second oen came later, saw that better images were available and started to adjust the track to the better images but got tired of it in the area you show?
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Many thanks to everyone who answered this has given me extra insight into how this particular situation arises, and how people may have attempted to resolve it.
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