QGIS » QGIS Application

I wrote the following to the GRASS user mailing list and was advised by Markus Neteler to open a QGIS bug report and point out that a bug might be in the following file: https://github.com/qgis/QGIS/blob/master/python/plugins/processing/algs/grass7/description/v.net.steiner.txt.

Here the problem description:
I am unable to figure out why a certain processing algorithm (v.net.steiner) works fine in QGIS2, but not in QGIS3. I am using the same line and point layer with the same cost column. The input data as well as the cost column are the only parameters that I define, the others remain the default ones.

In QGIS2 the processing history looks like this:

processing.runalg("grass7:v.net.steiner","C:/xxx/linesLayer.shp","C:/xxx/nodeLayer.shp",50,2,"1-100000","boundary",-1,False,"794057.939937,794307.889937,9833916.58837,9834082.13837",-1,0.0001,0,None)

The result looks fine connecting the 3 nodes via the line layer:
!!

In QGIS3 the processing history looks like this:

processing.run("grass7:v.net.steiner", {'input':'C:/xxx/linesLayer.shp','points':'C:/xxx/nodeLayer.shp','threshold':50,'arc_type':[0,1],'terminal_cats':'1-100000','acolumn':'boundary','npoints':-1,'-g':False,'output':'G:/1_QGIS_Temp_files/processing_f8ef30794232406cb21d5d7cc1d06809/4774808dfe284dafafd9a15a9879a5c1/output.shp','GRASS_REGION_PARAMETER':None,'GRASS_SNAP_TOLERANCE_PARAMETER':-1,'GRASS_MIN_AREA_PARAMETER':0.0001,'GRASS_OUTPUT_TYPE_PARAMETER':0})

The changed syntax in the history of QGIS2 and QGIS3 adds the parameter names to the history, which is a visual change only, while the parameters in both calls remain the same.

No result is created. The error messages indicate that the point layer cannot be used. However, the module has no points parameter (https://grass.osgeo.org/grass74/manuals/v.net.steiner.html):

FEHLER: v.net.steiner: Sorry, <points> is not a valid parameter

Importing the data to GRASS7 directly and running v.net.steiner there indicates the same, as I get the following error message:

Number of terminals: 0, ERROR: Nicht genügend Stationen (< 2)

I uploaded the subset of the line and point layer that I used here (https://share4land.itc.utwente.nl:5566/sharing/pfjsbL9G8).

Both QGIS2 and QGIS3 versions use GRASS7.4.