[Qgis-user] FW: Again a problem with legth

[Frederick Löbig]

Hey list... 
I again have a problem with analyzing vector-data:
I have a Polyline-Shapefile with EPSG:900913 Projection. I know, by measurements through Google Earth, that the total length of this line should be 1000m. I used the qGIS Ruler-Tool and checked that with "on the fly transf." on and it was 1000m as well. After that, I used the field-calculator and the $length-parameter in a "real"-field, but somehow it gives me out 1529.508 (m??)...
I've tried to detect a pattern in the differences between the attribute-table and the ruler results, but i didn't find any. 
I need to mesaure the exact length of polylines to analyze data-loss in subterrain-cables...
I really hope you can tell me how to fix that problem.. If you need any further Information:
qGIS 1.5.0Project-SRS: EPSG:900913Shapefile-SRS: EPSG:900913On the fly transformation: ONMeasure-Spheroid: WGS84
Thank you in advance..
Regards,Freddy


Frederick Löbig
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