[Qgis-user] Unit of length determined by layer or project CRS? (OTF on)

[magerlin]

I am a bit confused about what the unit of length is determined by: CRS for
layer or CRS for project (when OTF is on).

This post
<http://osgeo-org.1560.x6.nabble.com/RE-How-Do-I-Set-Field-Calculator-Units-For-Area-td4128975.html#a4128979> 
claims: "Calculations are in the project CRS unit if OTFR is enabled"

I have loaded OSM shapefiles from geofabrik.de which come in lat/lon (EPSG:
4326).

But since I show it on top of an OSM map using the OpenLayers plugin, the
project CRS is set to EPSG: 3857 (WGS 84 / Pseudo Mercator) and OTF is set
on.

EPSG: 3857 has in its definition "+units=m".

But when I in field calculator calculates the length using $length, the
lenght of a road section which is about 100 m long is calculated as about
0.001.

This indicates for me that it is calculated in degrees (due to the layer
CRS?)

Using the Qgis measure tool (with units set to meters) gives the expected
length of 100 m.



-----
Regards Morten

Currently using Qgis 2.10.1 (OSGeo4),
Windows 7, 64bit
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