Q:

Joining 2D polylines and DEM into 3D polylines using QGIS/GRASS/SAGA?

I have a road network in 2D/PostGIS and a DEM. I want to turn the road network into 3D by retrieving the Z-value from the DEM.
Both files are quiet large so an efficient process is needed. I'd prefer to use QGIS or any other open source tool.

A:

For that, you can use 

GRASS GIS with v.drape: Converts vector map to 3D by sampling of elevation 
raster map. 
SAGA GIS  with Shapes - Grid\Add Grid Values to Shapes
QGIS with GRASS v.drape in Sextante (QGIS 1.8) or Processing (QGIS 2.0)

QGIS with SAGA GIS "Add grid to shapes" in Processing (QGIS 2.0)

Python in the Python console with
raster.dataProvider().identify()

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