[Qgis-user] Profile tool - Error in the sampling points

[Martin Stubbs]

I have been using the profile tool plugin very successfully for some 
time but I now have an application where I need to know the coordinates 
of the sample points. I have added a few lines to the software to allow 
me to output the coordinates as well as the height points. This shows a 
problem with the calculation of the sample points.

I have a DXF file which I import in QGIS to use as the sample line. When 
I compare the points that were sampled to the original sample line I 
find a consistent error of approx 6m in the SE direction. I have tried 
converting the DXF line to a shapefile and the error is the same. I 
assume that the error is some type of projection error but all layers, 
the project and the DXF file are in the same EPSG:27700 (OSGB) projection.

I have created a much simpler DXF file and this doesn't show the error.

Does anyone have any ideas or suggestions?

Martin