[OSM-talk] Track offsets

[Steve Hill]

I've come across a problem with one of my methods of collecting tracks - 
I'm hoping someone might have some input:

I've got a computer in my car which connects to my (old style) eTrex 
Venture GPS via a serial cable.  The computer runs gpsd to talk to the 
GPS.  It also runs Kismet which does things like logging 802.11 networks, 
but most importantly Kismet talks to gpsd and logs the GPS track.  I then 
process the .gps file Kismet produces into a GPX file to use with OSM.

Now the problem - I recently compared the track downloaded from the GPS 
itself (using gpsbabel) with the track produced by Kismet and found they 
were fairly consistently offset from eachother by 100m or so.  I haven't 
worked out where this error is being introduced yet, but the GPS is set to 
WGS84 so I would expect the NMEA stream and the GPS's tracklog to match.

My next step is to look at the NMEA stream itself and see if that is 
correct, but has anyone else here had any similar problems that could 
shead some light onto what is going on?

  - Steve
    xmpp:steve at nexusuk.org   sip:steve at nexusuk.org   http://www.nexusuk.org/

      Servatis a periculum, servatis a maleficum - Whisper, Evanescence