[Qgis-user] how to use v.clean.advanced?

[Uwe Fischer]

Hello list,

 

I have a line shapefile (call it input.shp, derived from polygons) that i'd
like to turn it into clean lines (output.shp) using the processing toolbox
(PT). Clean lines means: no duplicates, broken at intersections. Dangles and
pseudo nodes are uninteresting here.

 

In my understanding, it's necessary to perform the following steps: 1. snap
vertices together within small threshold, 2. break lines, 2. remove
duplicates.

 

After entering my values and options in the v.clean.advanced input mask of
the PT, some problems and questions come up (I tried QGIS 2.10 and 2.12 on
Windows):

 

*         the PT input mask does not accept more than one value in the input
field for threshold. In fatal contrast to that, in the help text it reads
that there have to be multiple threshold values entered if multiple cleaning
tools are used. In my case, the box doesn't accept a comma separator nor an
additional numeric value.

 

*         the system puts together a command string (found in PT history)
containing values I never did enter and I don't want to use:

 

processing.runalg("grass:v.clean.advanced","D:/input.shp","snap,break,rmdupl
",0.01,"655282.346386,662305.603469,5871019.54139,5877018.65557",-1,0.0001,"
D:/output.shp",None)

 

*         please note the above values before "D:/output.shp": they smell
like default values for snapping and small area threshold, but I never did
choose those values! Where the hell do they come from?

 

*         the result is poor: lines are not broken and dups are not removed.

 

 

Does anybody know what went wrong?

 

 

Best regards, Uwe

 

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