[GRASS-user] r.thin quirk

[Dwight Needels]

On Jun 6, 2009, at 11:36 PM, Dwight Needels wrote:

> 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
>
> <r.thin.png>
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Although I figured out how to file a bug report on this, http://trac.osgeo.org/grass/ticket/636 
, I am not sure how to respond directly to comments on the ticket.

Hamish, I used the screenshot showing the vectors because I had  
already created it to look for artifacts. The extra line that makes  
the triangle is also present in the thinned raster (screenshot  
attached).

Thanks, -Dwight

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