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<p class="MsoNormal">Hello All,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m never sure which list to fire these GEOS problems from PostGIS issues to, so I’ll try them both this time.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m using the following:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">PostgreSQL 9.1.2 on i686-pc-linux-gnu, compiled by gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-44), 32-bit<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">POSTGIS="2.0.0alpha7SVN" GEOS="3.3.2-CAPI-1.7.2" PROJ="Rel. 4.7.1, 23 September 2009" LIBXML="2.6.26" USE_STATS<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I have been closely following the updates to GEOS / PostGIS at the end of last year with regards to overlay routines. Since the advent of ST_UnaryUnion and the updates in the BinaryOp code as of r3552 I have been trying to get our overlay
code working again. We currently do the following:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Break left layer and right layer into smaller regions (both are multipolygons)<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>For each region <o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="font-family:"Courier New","serif""><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Use ST_Snap to snap the left layer (which in this case is less accurate) to a collection of the right layer at 10E-8<o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="font-family:"Courier New","serif""><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Dump the left and the right layers to linework and collect them to two geoms<o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="font-family:"Courier New","serif""><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Perform a ST_UnaryUnion on each layer, then collect them together<o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="font-family:"Courier New","serif""><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Perform a ST_UnaryUnion on the collection (I found using this two tiered Union approach sometimes resolved nodding errors, obviously at the cost of speed though). If I get a non-noded intersection problem it is here 100% of the
time.<o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="font-family:"Courier New","serif""><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Polygonize the output<o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="font-family:"Courier New","serif""><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Perform overlay map to pull through gids from original left and right layers<o:p></o:p></p>
<p class="MsoListParagraph"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">At one point I did translate to the origin before any Union operations, but this broke down as the linework got more complex (which unfortunately happens every month as new polygons are added).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">At the moment the problem I face is the same as my old problem (when using ST_Union, see
<a href="http://trac.osgeo.org/geos/ticket/392">http://trac.osgeo.org/geos/ticket/392</a>). When performing the second ST_UnaryUnion of the collected left and right lineworks (which are valid) I get the following:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">GEOSUnion: TopologyException: found non-noded intersection between LINESTRING (149.169 -37.739, 149.169 -37.7391) and LINESTRING (149.169 -37.7391, 149.169 -37.739) at 149.16916209449002 -37.739087184984776<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">This year I’ve been familiarising myself with the code and reading through all the old posts I can find which apply to this.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I just wanted to throw this list post out there to see what others had to say about this issue. It seems to have been round for a while now, and from what I can tell it’s not an easy fix.
<o:p></o:p></p>
<p class="MsoNormal">Yum install<o:p></o:p></p>
<p class="MsoNormal">Is it likely to be a precision issue? I am currently upgrading my GCC version so I can try this
<a href="http://trac.osgeo.org/geos/ticket/504">http://trac.osgeo.org/geos/ticket/504</a>, does anyone have any thoughts on if that might help?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Or is the issue more likely to be as described here? <a href="http://trac.osgeo.org/geos/ticket/459">
http://trac.osgeo.org/geos/ticket/459</a><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Sorry for the long post, just hoping to get some discussion going. I will try to post a fresh testcase which causes the error tomorrow.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-size:9.0pt;font-family:"Verdana","sans-serif"">Cheers,<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-size:9.0pt;font-family:"Verdana","sans-serif";color:#999999">James Sewell </span><span style="font-size:9.0pt;font-family:"Verdana","sans-serif";color:#999999"><br>
</span><span style="font-size:9.0pt;font-family:"Verdana","sans-serif";color:#999999">Solutions Architect </span><span style="font-size:9.0pt;font-family:"Verdana","sans-serif";color:#999999"><br>
</span><span style="font-size:9.0pt;font-family:"Verdana","sans-serif";color:#999999">LISAsoft </span><span style="font-size:9.0pt;font-family:"Verdana","sans-serif";color:#999999"><o:p></o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:9.0pt;font-family:"Verdana","sans-serif";color:#999999">Ph: </span></b><span style="font-size:9.0pt;font-family:"Verdana","sans-serif";color:#999999">+61 3 8680 3250 <b>Fax: </b>+61 3 8680 3299 </span><span style="font-size:9.0pt;font-family:"Verdana","sans-serif";color:#999999"><br>
</span><span style="font-size:9.0pt;font-family:"Verdana","sans-serif";color:#999999">Level 9, 601 Bourke St, Melbourne Vic 3000<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Verdana","sans-serif";color:#999999"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Verdana","sans-serif";color:#4F81BD"><a href="http://www.lisasoft.com/"><span style="color:#4F81BD;text-decoration:none">http://www.lisasoft.com</span></a></span><span style="font-size:9.0pt;font-family:"Verdana","sans-serif";color:#999999"><br>
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