[postgis-users] How buffer trick validates features?

[Saka Royban]

hi
I'm so sorry. i was so mad because i didn't find ST_IsValidReason function 
myself. 

Thanks to PostGIS and its developers, it works nice.
Also, i found an option in OpenJump  for validating features.

Best Regards





________________________________
From: Saka Royban <sakaroyban at yahoo.com>
To: PostGIS Users Discussion <postgis-users at postgis.refractions.net>
Sent: Thu, December 30, 2010 11:57:42 AM
Subject: Re: [postgis-users] How buffer trick validates features?


Thanks  a lot Mr. Ramsey
one more question: is there a way to understand what is wrong with invalid 
feature? i.e. any software, package, etc.

sorry for simple questions. I'm a beginner.
Regards





________________________________
From: Paul Ramsey <pramsey at opengeo.org>
To: PostGIS Users Discussion <postgis-users at postgis.refractions.net>
Sent: Thu, December 30, 2010 12:00:14 AM
Subject: Re:  [postgis-users] How buffer trick validates features?

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
>
>
> _______________________________________________
> postgis-users mailing list
> postgis-users at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users
>
>
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