[postgis-users] negative buffer

Picavet Vincent 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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