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I tried the following in QGIS with the Grass Plugin:

r.cost input=preCostSurface@albi start_points=OSMroads@albi output=cost0109 max_cost=0

And I get the following error:

Dev note: Adapted sites library used for vector points. (module should be updated to GRASS 6 vector library)

No start points 
Finished with error

What is causing that and how can I fix it?

Edit: It seams like this is a general Grass 6.4.3 issue and will be resolved in Grass 7. Does anybody know a workaround for that problem meanwhile?

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The r.cost GRASS module expects start_points to be a map containing point features. It seems that your map doesn't contain any point features. Try using a map with point features. With QGIS you can easily digitize such a map.

For more information on the parameters see the r.cost manual page for GRASS 6.4:

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  • r.cost.rast takes as input a raster map with starting points. In other words a raster map where all non-NULL cells are considered to be starting points. Is this what your OSMroads map is?
    – Wolf Bergenheim
    Oct 31 '13 at 23:51
  • You are right. I used a line vector layer. I thought that works too. But it doesn't. It only accepts points. I converted the line layer to a raster and used r.cost.rast. This way it worked.
    – ustroetz
    Nov 4 '13 at 18:19

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