[postgis-users] ST_Buffer() never returns

[Martin Davis]

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


Andi Vajda wrote:
>
>  Hi,
>
> Running on Mac OS X 10.5.4 with 4gb of RAM and postgis_full_version() of
> POSTGIS="1.3.2" GEOS="3.0.0-CAPI-1.4.1" PROJ="Rel. 4.6.0, 21 Dec 2007" 
> USE_STATS
>
> I get a runaway postgres process if I call ST_Buffer(shape, 0.1) on 
> the attached WKT shape. My postgresql server eventually exhausts the 
> swap space over 9gb.
>
> It's a polygon with 12271 points representing the state of Alabama.
> When converted to GeoJSON it renders correctly at [1].
> Is this shape triggering some bug ?
>
> Thanks !
>
> Andi..
>
> [1] http://openlayers.org/dev/examples/vector-formats.html
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-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022