[GRASS-user] r.thin quirk

Dwight Needels needels at translucida.com
Sat Jun 6 23:36:45 EDT 2009

Hi all. I have run into a quirk using r.thin, but I am not sure  
whether or not it is a bug. I have a raster that was generated from  
multiple GPS tracks using v.rast followed by r.buffer. Using r.thin  
followed by r.to.vect creates a vector that must then be cleaned using  
v.clean to remove dangles (so far, so good).

The quirk is that r.thin occasionally creates a triangle at the  
intersection of two lines instead of two intersecting lines. All of  
the examples I have seen involve relatively acute angles (less than 25  
degrees??). I have attached a screenshot that shows the raster in  
magenta, the vector with dangles in white, and the cleaned vector as  
(a thinner) green. There are numerous acute angles that generate the  
vectors I would expect, with one exception in the center.

Is this expected behavior? If so, is there an easy way to search for  
all such resulting triangles in a vector or to remove all such extra  
lines in a vector? If not, is there a way to fix it?

Thanks, -Dwight

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