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I have a set of vector lines in grass which I need to convert into polygons. However, because of bad base data, the polygons don't always close. To fix this, I need to extend each disjointed line by a certain distance and connect it to the first line it hits. The problem is that I can't figure out how to do this. I have experimented with v.clean, v.generalize, v.edit, and (converting to a thinned raster) r.grow, r.neighbors and even r.flow, but I can't find anything which will let me do this.

Can anyone point me to a tool that would do this?

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You should use the tool v.clean with the option tool=snap and specify the correct thresh setting to snap the lines to the closest vertex. More details can be found here [1]

[1] http://grass.osgeo.org/gdp/html_grass64/v.clean.html

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  • I tried that, but there are two problems: 1, it seems to snap to the first point found in threshold, not necessarily the closest. And 2, it also snaps ends which are already joined together. Am I doing something wrong?
    – aquavitae
    Commented Sep 14, 2012 at 12:21
  • if there aren't too many polygons to edit, you could the use vector digitizer in the wxgui grass.osgeo.org/grass64/manuals/html64_user/…
    – dmci
    Commented Sep 14, 2012 at 12:33
  • Only a few million... It definitely needs to be automatible.
    – aquavitae
    Commented Sep 14, 2012 at 13:37
  • ... then grass.osgeo.org/gdp/html_grass64/v.edit.html will be interesting.
    – markusN
    Commented Sep 14, 2012 at 14:32
  • I looked at v.edit, but can't see a way to do it with that either.
    – aquavitae
    Commented Sep 26, 2012 at 12:07

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