[postgis-users] negative buffer
Vincent.Picavet at mediapost.fr
Wed Jan 21 01:35:32 PST 2009
> I have polygons with sometimes very peculiar shapes
> representing the distribution limits of specific types of
> sediments (e.g. channel-like branching, fluvial fans...).
> When I try to create positive and negative buffers of that
> polygons using the combined
> (st_buffer(st_simply(geom,i)j)-method I succeed only in
> positive direction. In negative direction it very fastly
> violates enforce_geotype_geom-check. When I look on the last
> results I see, it is related to the channel-like branches.
> Using the buffer-method in ArcGIS it works as expected. Is
> there a clever method getting it work in PostGIS too?
As for getting negative buffers to be valid geometries, I generally use
the 0-buffer trick as in :
st_buffer(st_buffer(geom, -i), 0). Not 100% sure it will work but it
generally fixes a lot of problems.
Let us know of the results if you try that with your data.
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