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I'm cleaning up a (very) messy shapefile in QGIS/Grass.

I now have several large polygons with numerous (100s) of small rings.

Is there a quick and easy way to remove/ fill all these small rings. Selecting and deleting each one manually is not feasible.

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do you mean small polygons instead of small rings? – dmci Dec 10 '12 at 14:03
They are empty spaces, so rings – Andy Harvey Dec 10 '12 at 14:34
have you tried using v.clean tool=rmarea thresh=... – dmci Dec 10 '12 at 16:03
Thanks dcmi, yes I have tried rmarea but it does not seem to be working. Can you confirm, should this work on rings, or only on slivers between polygons. Perhaps I am using the tool incorrectly? – Andy Harvey Dec 10 '12 at 16:22
what type is shapefile polygon or linestring ? – simplexio Jan 10 at 9:40

1 Answer

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If you need to fill small "donut holes" you might try the buffer-out/buffer-in trick. You create a buffer of your polygons just large enough to fill the holes. Then buffer that polygon layer again with the same value but negative (i.e. buffer inside). The problem with this method is that is does change the outer boundary slightly. If the holes are small, this might not make too much of a difference. (From what you describe as "rings", they seem to empty areas, not part of the surrounding polygon, so v.clean tool=rmarea won't work)

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thanks micha, thats what i thought RE v.clean.rmarea. The buffer idea is a good one, but I don't think will work in this case. Some of the rings are relatively large, and I need to keep the outer boundary's position. Looks like manual delete is the only way to go....? – Andy Harvey Dec 11 '12 at 8:21
Andy, consider also the threshold parameter for the tools to pick only those of interest. And see also v.edit which also supports to spatially constrain operations. Eventually, consider to use GRASS 7 for that which has even more topological tools. – markusN Feb 9 at 9:24

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