[postgis-users] ST_Buffer() never returns

[Andi Vajda]

On Fri, 12 Sep 2008, Martin Davis wrote:

> This is an example of a known issue with GEOS/JTS buffering.  The problem 
> occurs when using a relatively large buffer distance on geometries which have 
> a large number of vertices which are relatively dense (i.e. the distance 
> between adjacent vertices is much smaller than the requested buffer 
> distance).
>
> A couple of ways to avoid this problem are:
> - simplify the input geometry using a tolerance which gets rid of most of the 
> very dense vertices (use a tolerance of say from 1% to 10% of the buffer 
> distance)
> - buffer the geometry mulitple times, starting with a very small buffer 
> distance and gradually increasing it

Thanks, with your tip, I defined the following function which made it 
work (and fast) for all the shapes in my db:

CREATE OR REPLACE FUNCTION gix_make_shell(geometry)
RETURNS geometry AS $$
     SELECT ST_Simplify(ST_Buffer(ST_Simplify(ST_Buffer(ST_Simplify(ST_Buffer(ST_Simplify(ST_Buffer($1, 
0.0001), 0.0001), 0.001), 0.001), 0.01), 0.01), 0.1), 0.1)
$$ LANGUAGE SQL STABLE;

Andi..