[talk-au] Accuracy of overhead imagery vs GPS traces

[Matt White]

What do we regard as more correct - the yahoo imagery or GPS traces?

I just uploaded about 4 hours of GPS traces at 1 sec intervals, and went to
do some mapping only to find someone had beaten me to it. However, the roads
seemed to be permanently offset to the south compared to my traces (but
right over the road placement when compared to the Yahoo maps). My GPS was
reported a + or - of about 3 or 4 metres the entire time (Garmin GPSMAP
60Csx).

Most other places I've mapped, tjhe imagery seems spot on compared to the
GPS traces, but this time round, it just seems consistently out.
Unfortunately, it looks like the only set of hi res traces for this area are
mine, so we may actually be dealing with that 4 metre variation - no other
traces to compare it to (unless someone has some private traces that only
they can see).

To see exactly what I'm talking about, have a look at Authurs seat in the
Mornington Peninsula near Melbourne. It's a nice curly road, buit everything
seems offset.  

http://www.openstreetmap.org/?lat=-38.34866&lon=144.95017&zoom=16&layers=B0F

Oh yeah - I'm doing this in Potlatch, not JOSM. My pooter isn't being
particularly co-operative when it comes to running JOSM.

Matt
-------------- next part --------------
A non-text attachment was scrubbed...
Name: winmail.dat
Type: application/ms-tnef
Size: 2212 bytes
Desc: not available
URL: <http://lists.openstreetmap.org/pipermail/talk-au/attachments/20071202/d8923d04/attachment.bin>