[GRASS-user] Criteria for v.clean tool=rmdangle

[Dwight Needels]

The rmdangle tool in v.clean usually behaves exactly the way I would  
expect it to, but occasionally it does not.

I have a vector generated from a raster using r.thin and r.to.vect  
that has numerous dangles. In the attached screenshot there are what  
appear to be two dangles with lengths of ~2 and ~5 ft. The two  
terminal polylines of what appears to be the core vector are 16 ft and  
11 ft (27 ft combined). The pre-clean vector is gray, the cleaned  
vector is red, vertices are displayed as points derived using  
v.to.points.

After running v.clean tool=rmdangle thresh=30 the resulting vector (in  
red) removes one of the dangles plus what appears to be the two  
terminal polylines of the core  vector, while leaving the smaller  
dangle attached. I tried running v.edit tool=merge or  
v.build.polylines before cleaning, but got the same results.

How does v.clean decide which line segment to remove as a dangle? Is  
there a way to force it to remove the line segment that leaves the  
longest possible remaining vector?

My workaround has been to run v.clean repeatedly with increasing  
thresholds, which I think removes the shortest line segment on each  
pass.

Thanks, -Dwight

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