[OSM-newbies] difference between yahoo WMS and gps track

[Jonas Stein]

Both datasources have their weaknesses. I want to understand the
errorfunction of both better to get most out of the data.

Lets assume
The Garmin 76SCx tracks with 1 Point/s it shows +/-4 m in Display (1)
WAASG and EGNOS is enabled. Compass = ON

The track shows in JOSM as a very smooth line. Walking on one other side 
of the street back shows a parallel dotted line like . and '
Then i draw a way in the middle the WMS pendant is shifted 
10 to 30 metres but has same shape.


======================


......................->
------------------------
<-''''''''''''''''''''''


=  wms
.' GPX Track
-  mean line


1) where does this information come from?
2) has the gpx track an offset?
3) are there any tricks to get rid of that difference locally?


When i walk a circle with the gps the data forms a very precise circle. 

Kind regards,

-- 
Jonas Stein <news at jonasstein.de>