[GRASS-user] r.thin ?

[Micha Silver]

charlie wrote:

> Hi.  I am currently using Grass 6.4 on linux and beginning the the 
> process of vectorizing an old NOAA raster map with r.thin. The map is 
> approximately 12,000 pixels by 8,000 pixels wide.
>
> According to this post, ( 
> http://osgeo-org.1803224.n2.nabble.com/r-thin-td2718260.html#a2718260 
> )the iteration variable has to be equal or larger than half the number 
> of cells of the wider line so I increased the iterations to 6,000, and 
> it would up finishing in approximately 4,200 passes.
>
> Previously, I was getting excellent preliminary results, with fewer 
> (1,000) iterations,  distinct features were visible, however at least 
> 50% of the map was not completed. 
>
> Now with an increase to 6,000 iterations r.thin completes, but the 
> results are a single 1px wide horizontal line.  Im sure I am 
> overlooking something relatively simple; can anyone give me any advice 
> on how to best run r.thin in this particular case?
>

What is it you are trying to do? The r.thin module is designed to make 
line features in a raster exactly one pixel wide so that when converting 
to a line vector, the line will be clean.
If you run r.thin on a raster that represents areas, and give a high 
enough iteration value, the areas will eventually be reduced to lines.

>
> Thanks!
>
> Charlie
>
>
> <a href="www.wetlandresearch.com">Wetlands</a>
>
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