[Qgis-user] Incorrect Results in Buffer

[Frederick Löbig]

Hi there,
I have a problem using the buffer function in qGIS 1.6.0:
The situation: I have my project SRS set to EPSG:900913 (web mercator). As a layer I have a line-layer also with EPSG:900913 as a projection. The project-wide units are meters. I now want to add a 250m buffer around the lines so i click vector->geoprocessing tools->Buffer(s), select my line-layer, type in 250 for 250 meters, check dissolve buffer results ans set a filename. Then the buffer is created, but unfortunately, when I export the buffer as kml and check the buffer width in Google Earth it is around 150-160 meters, so far off my 250meters. I also checked the distance with the qGIS measurement-tool - same result. 
The lines are located in London. I have tried to use simple WGS84 and the british nationale grind, but none of them worked.
This has to do something with differente base-ellipsoids I think, but I did not get to the bottom of the problem. 
Could anybody please help me with this?

Frederick Löbig
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