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List: postgis-users
Subject: Re: [postgis-users] How buffer trick validates features?
From: Saka Royban <sakaroyban () yahoo ! com>
Date: 2010-12-30 21:26:30
Message-ID: 447570.18655.qm () web121609 ! mail ! ne1 ! yahoo ! com
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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@yahoo.com>
To: PostGIS Users Discussion <postgis-users@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@opengeo.org>
To: PostGIS Users Discussion <postgis-users@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@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@postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users
>
>
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<html><head><style type="text/css"><!-- DIV {margin:0px;} \
--></style></head><body><div style="font-family:times new roman,new \
york,times,serif;font-size:12pt"><div>hi<br>I'm so sorry. i was so mad because i \
didn't find ST_IsValidReason function myself. <br>Thanks to PostGIS and its \
developers, it works nice.<br>Also, i found an option in OpenJump for \
validating features.<br><br>Best Regards<br><br></div><div style="font-family: times \
new roman,new york,times,serif; font-size: 12pt;"><br><div style="font-family: times \
new roman,new york,times,serif; font-size: 12pt;"><font face="Tahoma" size="2"><hr \
size="1"><b><span style="font-weight: bold;">From:</span></b> Saka Royban \
<sakaroyban@yahoo.com><br><b><span style="font-weight: bold;">To:</span></b> \
PostGIS Users Discussion <postgis-users@postgis.refractions.net><br><b><span \
style="font-weight: bold;">Sent:</span></b> Thu, December 30, 2010 11:57:42 \
AM<br><b><span style="font-weight: bold;">Subject:</span></b> Re: [postgis-users] \
How buffer trick validates features?<br></font><br> <meta \
http-equiv="x-dns-prefetch-control" content="off"><div style="font-family: times new \
roman,new york,times,serif; font-size: 12pt;">Thanks a lot Mr. Ramsey<br>one \
more question: is there a way to understand what is wrong with invalid feature? i.e. \
any software, package, etc.<br><br>sorry for simple questions. I'm a \
beginner.<br>Regards<br><div><br></div><div style="font-family: times new roman,new \
york,times,serif; font-size: 12pt;"><br><div style="font-family: \
arial,helvetica,sans-serif; font-size: 13px;"><font face="Tahoma" size="2"><hr \
size="1"><b><span style="font-weight: bold;">From:</span></b> Paul Ramsey \
<pramsey@opengeo.org><br><b><span style="font-weight: bold;">To:</span></b> \
PostGIS Users Discussion <postgis-users@postgis.refractions.net><br><b><span \
style="font-weight: bold;">Sent:</span></b> Thu, December 30, 2010 12:00:14 \
AM<br><b><span style="font-weight: bold;">Subject:</span></b> Re: [postgis-users] \
How buffer trick validates features?<br></font><br> In order to buffer a feature you \
have to create a new set of line work<br>then build a polygon from that. If the new \
set of linework is the old<br>set, the built feature looks much line the old one. But \
because it's<br>built by the database (by GEOS, in this case) it is built according \
to<br>the known topology rules we want, and hence is more likely to \
be<br>valid.<br><br>P.<br><br>On Wed, Dec 29, 2010 at 12:21 PM, Saka Royban <<a \
rel="nofollow" ymailto="mailto:sakaroyban@yahoo.com" target="_blank" \
href="mailto:sakaroyban@yahoo.com">sakaroyban@yahoo.com</a>> wrote:<br>> Hi \
all.<br>> I was reviewing postgis workshop presented in FOSS4G 2007. it presents \
a<br>> trick like this for making invalid features valid:<br>> UPDATE \
bc_voting_areas<br>> SET the_geom = ST_Buffer(the_geom, 0.0)<br>> WHERE gid = \
4897;<br>><br>> I'm wondering how it works in background!!!. I mean how \
buffering with zero<br>> distance makes features valid?<br>> what is in buffer
function?<br>><br>> Regards<br>><br>><br>> \
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