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<div class="Normal"><span style='font-size: 10pt; '>Yes I made a mistake Robert
posts the correct link. Thank you Robert.</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>Regards</span><br><span style='font-size: 10pt; '>Horst</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>------------------------------------------------</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>Dr. Horst
Düster</span><br><span style='font-size: 10pt; '>GIS-Koordinator, Stv.
Amtschef</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>Kanton
Solothurn</span><br><span style='font-size: 10pt; '>Bau- und
Justizdepartement</span><br><span style='font-size: 10pt; '>Amt für
Geoinformation</span><br><span style='font-size: 10pt; '>SO!GIS
Koordination</span><br><span style='font-size: 10pt; '>Rötistrasse
4</span><br><span style='font-size: 10pt; '>CH-4501 Solothurn</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>Telefon ++41(0)32 627 25
32</span><br><span style='font-size: 10pt; '>Telefax ++41(0)32 627 22
14</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>mailto:horst.duester@bd.so.ch</span><br><span style='font-size: 10pt; '>http://www.agi.so.ch</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>-----Ursprüngliche
Nachricht-----</span><br><span style='font-size: 10pt; '>Von: Burgholzer,Robert
[mailto:rwburgholzer@deq.virginia.gov]</span><br><span style='font-size: 10pt; '>Gesendet
am: Freitag, 29. August 2008 15:02</span><br><span style='font-size: 10pt; '>An:
PostGIS Users Discussion</span><br><span style='font-size: 10pt; '>Betreff: RE:
[postgis-users] ST_Unioning invalid multipolygons</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>http://www.sogis1.so.ch/sogis/dl/postgis/cleanGeometry.sql
</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>you need caps on the "G" in
geometry.</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>Robert W.
Burgholzer</span><br><span style='font-size: 10pt; '>Surface Water
Modeler</span><br><span style='font-size: 10pt; '>Office of Water Supply and
Planning</span><br><span style='font-size: 10pt; '>Virginia Department of
Environmental
Quality</span><br><span style='font-size: 10pt; '>rwburgholzer@deq.virginia.gov</span><br><span style='font-size: 10pt; '>804-698-4405</span><br><span style='font-size: 10pt; '>Open
Source Modeling
Tools:</span><br><span style='font-size: 10pt; '>http://sourceforge.net/projects/npsource/</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>-----Original
Message-----</span><br><span style='font-size: 10pt; '>From:
postgis-users-bounces@postgis.refractions.net
[mailto:postgis-users-bounces@postgis.refractions.net] On Behalf Of Stephan
Holl</span><br><span style='font-size: 10pt; '>Sent: Friday, August 29, 2008
4:35 AM</span><br><span style='font-size: 10pt; '>To: PostGIS Users
Discussion</span><br><span style='font-size: 10pt; '>Cc:
Horst.Duester@bd.so.ch</span><br><span style='font-size: 10pt; '>Subject: Re:
[postgis-users] ST_Unioning invalid multipolygons</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>Hello Horst,</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>Düster Horst
<Horst.Duester@bd.so.ch>, [20080829-09:02:02]:</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>>
Mmmmm...</span><br><span style='font-size: 10pt; '>> >Another solution
which *may* work is to replace the geometry by
a</span><br><span style='font-size: 10pt; '>> buffer
</span><br><span style='font-size: 10pt; '>> >of size 0 around the
geometry in your select statement
</span><br><span style='font-size: 10pt; '>>
</span><br><span style='font-size: 10pt; '>> No this is a bad idea. You do
not have any control about the result
of</span><br><span style='font-size: 10pt; '>> your buffer(0). A better way
is to clean the polygon geometry with
the</span><br><span style='font-size: 10pt; '>> cleangeometry() function you
can download from:</span><br><span style='font-size: 10pt; '>>
</span><br><span style='font-size: 10pt; '>>
http://www.sogis1.so.ch/sogis/dl/postgis/cleangeometry.sql</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>This link seems to be wrong,
I get a 404.</span><br><span style='font-size: 10pt; '>Could you post the
correct link to this
interesting-sounding</span><br><span style='font-size: 10pt; '>function,
please?</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>> The function cleans by
breaking the self-intersecting parts of
your</span><br><span style='font-size: 10pt; '>> geometry into
multigeometries.</span><br><span style='font-size: 10pt; '>>
</span><br><span style='font-size: 10pt; '>> Sometimes postgis throws
topology exeptions although your geometry
is</span><br><span style='font-size: 10pt; '>> valid. In this case geos by
itself produces the error. Maybe this
is</span><br><span style='font-size: 10pt; '>> the result of rounding
problems and you don't have any chance
to</span><br><span style='font-size: 10pt; '>> solve the
problem.</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>best regards from
Osna</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '> Stephan</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>>
</span><br><span style='font-size: 10pt; '>> -----Ursprüngliche
Nachricht-----</span><br><span style='font-size: 10pt; '>> Von: Michael
Michaud
[mailto:michael.michaud@free.fr]</span><br><span style='font-size: 10pt; '>>
Gesendet am: Freitag, 29. August 2008
08:24</span><br><span style='font-size: 10pt; '>> An: PostGIS Users
Discussion</span><br><span style='font-size: 10pt; '>> Betreff: Re:
[postgis-users] ST_Unioning invalid
multipolygons</span><br><span style='font-size: 10pt; '>>
</span><br><span style='font-size: 10pt; '>> David Jantzen a écrit
:</span><br><span style='font-size: 10pt; '>> > Hi
again,</span><br><span style='font-size: 10pt; '>>
></span><br><span style='font-size: 10pt; '>> > I'm trying to ST_Union
multipolygons from the Zillow
neighborhood</span><br><span style='font-size: 10pt; '>>
data.</span><br><span style='font-size: 10pt; '>> > When I do this I
occasionally see:</span><br><span style='font-size: 10pt; '>>
></span><br><span style='font-size: 10pt; '>> > NOTICE:
TopologyException: found non-noded intersection
between</span><br><span style='font-size: 10pt; '>> >
-73.812....</span><br><span style='font-size: 10pt; '>>
></span><br><span style='font-size: 10pt; '>> > This appears to be due
to invalid geometries, as the following
query</span><br><span style='font-size: 10pt; '>> > returns over a hundred
rows:</span><br><span style='font-size: 10pt; '>>
></span><br><span style='font-size: 10pt; '>> > select * from
neighborhoods where not
ST_IsValid(the_geom)</span><br><span style='font-size: 10pt; '>>
></span><br><span style='font-size: 10pt; '>> > Can anyone suggest a
workaround here? The resulting geometry
needs</span><br><span style='font-size: 10pt; '>> > to be a multipolygon.
Also, what is ST_Is_valid actually
testing</span><br><span style='font-size: 10pt; '>> >
for?</span><br><span style='font-size: 10pt; '>>
The</span><br><span style='font-size: 10pt; '>> > documentation isn't very
explicity about the definition of
validity.</span><br><span style='font-size: 10pt; '>> >
</span><br><span style='font-size: 10pt; '>> Most of time, invalid polygons
are polygons with a self intersecting
</span><br><span style='font-size: 10pt; '>> boundaries (as in the number
'8') or self-touching boundary (two non
</span><br><span style='font-size: 10pt; '>> contiguous points of the
boundary are touching each other)</span><br><span style='font-size: 10pt; '>>
The best solution is to correct those geometries if you
can.</span><br><span style='font-size: 10pt; '>> Another solution which *may*
work is to replace the geometry by
a</span><br><span style='font-size: 10pt; '>>
buffer</span><br><span style='font-size: 10pt; '>>
</span><br><span style='font-size: 10pt; '>> of size 0 around the geometry in
your select statement (using a</span><br><span style='font-size: 10pt; '>>
0-buffer</span><br><span style='font-size: 10pt; '>>
</span><br><span style='font-size: 10pt; '>> is a work-around which generally
works with JTS library from which
</span><br><span style='font-size: 10pt; '>> postgis functions are
derived).</span><br><span style='font-size: 10pt; '>>
</span><br><span style='font-size: 10pt; '>> Michaël</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>--
</span><br><span style='font-size: 10pt; '>Stephan Holl
<stephan.holl@intevation.de>,
http://intevation.de/~stephan</span><br><span style='font-size: 10pt; '>Tel: +49
(0)541-33 50 8 32 | Intevation GmbH | AG Osnabrück - HR B
18998</span><br><span style='font-size: 10pt; '>Geschäftsführer:
Frank Koormann, Bernhard Reiter, Dr. Jan-Oliver
Wagner</span><br><span style='font-size: 10pt; '>_______________________________________________</span><br><span style='font-size: 10pt; '>postgis-users
mailing
list</span><br><span style='font-size: 10pt; '>postgis-users@postgis.refractions.net</span><br><span style='font-size: 10pt; '>http://postgis.refractions.net/mailman/listinfo/postgis-users</span></div>
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