[postgis-users] How buffer trick validates features?

Paul Ramsey pramsey at opengeo.org
Wed Dec 29 12:30:14 PST 2010


In order to buffer a feature you have to create a new set of line work
then build a polygon from that. If the new set of linework is the old
set, the built feature looks much line the old one. But because it's
built by the database (by GEOS, in this case) it is built according to
the known topology rules we want, and hence is more likely to be
valid.

P.

On Wed, Dec 29, 2010 at 12:21 PM, Saka Royban <sakaroyban at yahoo.com> wrote:
> Hi all.
> I was reviewing postgis workshop presented in FOSS4G 2007. it presents a
> trick like this for making invalid features valid:
> UPDATE bc_voting_areas
> SET the_geom = ST_Buffer(the_geom, 0.0)
> WHERE gid = 4897;
>
> I'm wondering how it works in background!!!. I mean how buffering with zero
> distance makes features valid?
> what is in buffer function?
>
> Regards
>
>
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