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

[Goyo]

2010/12/5 Frederick Löbig <frederick.loebig at live.de>:
> 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 can confirm this in trunk. The problem seems to be projection
dependant as it does not happen using EPSG:23030. I guess you can get
correct measures by reprojecting your shapefiles into a suitable UTM
srs (you may have to change the project crs too, I did not test this).
Far from ideal but it can help you to get the work done.

Goyo