[GRASSLIST:4074] Re: vectorizing rasters

[Hamish]

> I have a some scanned maps (black and white, essentially line art)
> that I have imported into a grass53 xy location. I am looking for more
> efficient ways to convert them to vector files than heads up
> digitizing with v.digit.
> 
> I have tried r.thin and v.line. However, the resultant map has got
> lots of little dangles that hang off "real" lines. I was going to try
> using v.trim to remove them (my guess is that they are around 2 -3
> pixels in length), but I'm getting "v.trim command not found", was
> v.trim removed from 53?
> 
> That being said, an even bigger problem is all the little 2 to 5 pixel
> line segments the within the enclosed polygons. These are a result of 
> trying to vectorize a raster that had bunches of little dots all over 
> the place that had nothing to do with the actual line art of the map, 
> but were created by the scanner as a representation of paper color.

v.trim was disabled apparently because it was buggy. If you compiled from
source code, you can always compile the individual module with:

cd src/mapdev/v.trim
gmake53

.. see
http://freegis.org/cgi-bin/viewcvs.cgi/*checkout*/grass/src/mapdev/v.trim/BUGS



instead try:

[GRASS 5.3]
v.rm.dangles


[GRASS 5.7]
v.clean tool=rmdangle thresh=
     or tool=chdangle  + v.extract
     or tool=rmarea  (or v.extract -d)



Hamish