> Having been adding items into osm for the last year I've noticed people
> spending a lot of time tracing roads from landsat, yahoo, etc.
> While this is admirable work is this really a useful exercise. Someone
> will eventually drive along this road with a gps upload it and then erase
> the traced road.
This is the reason I have stopped wasting time loading roads in to OSM.
I got very keen and loaded lots of roads by tracing them off Yahoo maps,
making sure the trace was an accurate reflection of reality. Then someone
overwrote my plots with a GPS track that was the result of driving these
roads once, with no understanding of the unavoidable inaccuracies in GPS
The straight plot of what I knew was straight road was replaced by a wavy
line. I gave up.
> I got very keen and loaded lots of roads by tracing them off Yahoo maps,
> making sure the trace was an accurate reflection of reality. Then someone
> overwrote my plots with a GPS track that was the result of driving these
> roads once, with no understanding of the unavoidable inaccuracies in GPS
> The straight plot of what I knew was straight road was replaced by a wavy
> line. I gave up.
What about the copyright ramifications of tracing maps? I've done a lot of GPS
tracks and through making multiple passes at various times I've found them
very accurate. Frequently I've found real maps having curves that aren't
there and the GPS is more accurate. It depends on the quality of the GPS fix
and how many times you go over it, if it's just been done once, well chances
are it's could be 10-25m out.
> The lesson remains that multiple passes with GPS provides best data.
in my area i've found the ariel photo to be out by as much as 100m.
several GPS passes are with in 10-15m of each other.
my gps is the usb dongle type, and i decided that putting it on
the right hand side of the car yields more consistent traces when
making several trips along the same roads.
for dual dual carriage ways, it probaly doesn't make any difference.
the lanes are so wide that you can sit on the left side of the left
lane, or the right side of the left lane or left or right side of
the right lane and still get data traces that are 20m wide!
Operating Systems, Services and Operations
Information Technology Services, The University of Adelaide