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</o:shapelayout></xml><![endif]--></head><body lang=EN-AU link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='color:#1F497D'>Sorry, I didn’t include the actual error:<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>An example is:<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal>NOTICE: TopologyException: found non-noded intersection between LINESTRING (143.861 -36.881, 143.861 -36.881) and LINESTRING (143.861 -36.881, 143.861 -36.881) at 143.861 -36.881<o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>This particular one is a two very small identical lines, this isn’t always the case but seems to be the majority of the time.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><div><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-size:9.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>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 <br>Developer <br>LISAsoft <o:p></o:p></span></p><div><div><div><div><div class=MsoNormal><span style='font-size:9.0pt;font-family:"Verdana","sans-serif";color:#999999'><hr size=2 width=420 style='width:315.0pt' align=left></span></div></div></div></div></div><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 <br>Level 9, 601 Bourke St, Melbourne Vic 3000<o:p></o:p></span></p><div><div><div><div><div class=MsoNormal><span style='font-size:9.0pt;font-family:"Verdana","sans-serif";color:#999999'><hr size=2 width=420 style='width:315.0pt' align=left></span></div></div></div></div></div><p class=MsoNormal><span style='font-size:9.0pt;font-family:"Verdana","sans-serif";color:#999999'><br>LISAsoft is part of the A2end Group of Companies<br></span><span style='font-size:9.0pt;font-family:"Verdana","sans-serif";color:#4F81BD'><a href="http://www.ardec.com.au/"><span style='color:#4F81BD;text-decoration:none'>http://www.ardec.com.au</span></a><br><a href="http://www.lisasoft.com/"><span style='color:#4F81BD;text-decoration:none'>http://www.lisasoft.com</span></a><br><a href="http://www.terrapages.com/"><span style='color:#4F81BD;text-decoration:none'>http://www.terrapages.com</span></a></span><span style='color:#1F497D'><o:p></o:p></span></p></div><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> James.Sewell@lisasoft.com <br><b>Sent:</b> Wednesday, 12 January 2011 12:06 PM<br><b>To:</b> 'geos-devel@lists.osgeo.org'<br><b>Subject:</b> GEOS errors from PostGIS<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Hello All,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I am currently creating an OSS Python app which uses PostGIS (and thus GEOS) to combines multiple layers and carries through attributes.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I am using a method derived from Paul Ramsey’s <a href="http://s3.opengeo.org/postgis-power.pdf">http://s3.opengeo.org/postgis-power.pdf</a> document. The steps I am taking are as follows:<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 lfo2'><![if !supportLists]><span style='font-family:Symbol'><span style='mso-list:Ignore'>·<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]>Take the left and right layers and split them into smaller segments<o:p></o:p></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l0 level1 lfo2'><![if !supportLists]><span style='font-family:Symbol'><span style='mso-list:Ignore'>·<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]>Iterate through the segments doing the following:<o:p></o:p></p><p class=MsoListParagraph style='margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo2'><![if !supportLists]><span style='font-family:"Courier New"'><span style='mso-list:Ignore'>o<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]>Use the following to dump each side to linework<o:p></o:p></p><p class=MsoListParagraph style='margin-left:72.0pt'><o:p> </o:p></p><p class=MsoNormal style='margin-left:72.0pt'>SELECT ST_Collect(a.the_geom) AS the_geom <o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'> FROM (SELECT <o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'> (ST_Dump<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'> (ST_Exteriorring(<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'> (ST_Dumprings(<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'> (ST_Dump(the_geom)).geom)).geom))).geom AS the_geom<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoListParagraph style='margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo2'><![if !supportLists]><span style='font-family:"Courier New"'><span style='mso-list:Ignore'>o<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]>Put two resulting multi-polygons into a table, make sure they are valid (and all encapsulated polys are valid), and union to remove overlap as follows<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal style='margin-left:72.0pt'>SELECT ST_Union(ST_snaptogrid(the_geom,10E-10)) AS the_geom <o:p></o:p></p><p class=MsoNormal style='margin-left:72.0pt'><o:p> </o:p></p><p class=MsoListParagraph style='margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo2'><![if !supportLists]><span style='font-family:"Courier New"'><span style='mso-list:Ignore'>o<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]>Build the polygons back up as follows<o:p></o:p></p><p class=MsoNormal style='margin-left:36.0pt'><o:p> </o:p></p><p class=MsoNormal style='margin-left:72.0pt'>SELECT a.the_geom AS the_geom, <o:p></o:p></p><p class=MsoNormal style='margin-left:72.0pt'> ST_pointonsurface(a.the_geom) AS point, <o:p></o:p></p><p class=MsoNormal style='margin-left:72.0pt'> 0 AS leftgid, 0 AS rightgid <o:p></o:p></p><p class=MsoNormal style='margin-left:72.0pt;text-indent:36.0pt'>FROM (SELECT (ST_Dump(ST_polygonize(the_geom))).geom AS the_geom<o:p></o:p></p><p class=MsoNormal style='margin-left:72.0pt'><o:p> </o:p></p><p class=MsoNormal style='margin-left:72.0pt'><o:p> </o:p></p><p class=MsoListParagraph style='margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo2'><![if !supportLists]><span style='font-family:"Courier New"'><span style='mso-list:Ignore'>o<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]>Then use an overlay to map the attributes back through from the left and the right.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The process works, however I am getting problems with GEOS Non Noded Intersection <span style='color:#1F497D'>(“GEOS union() threw an error!”) </span>crashes in some areas. These can often be fixed by rearranging the data (importing in a different order, snapping to a slightly different grid etc...). <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>When a failure occurs I am given two linestrings and a point, however these usually bear no relationship to the lines in either the expected output, the left or the right side other than being in the same area.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Unfortunately I can’t provide data at the moment as any attempt to reduce the size of the dataset seems to remove (or relocate) the problem. I will try and get permission to release some data from the customer, but this will take some time.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>One thing to note is that the layers I am combining contain very complex and very similar linework. It would not be unexpected to get 10 sets of similar but not identical linework all running around an area. This is acceptable for the end product, but I am wondering if it is upsetting the Union somehow?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>If anyone has any ideas they would be most appreciated.<o:p></o:p></p><p class=MsoListParagraph style='margin-left:108.0pt'><o:p> </o:p></p><p class=MsoNormal style='margin-left:72.0pt'> <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 <br>Developer <br>LISAsoft <o:p></o:p></span></p><div><div><div><div><div><div><div class=MsoNormal><span style='font-size:9.0pt;font-family:"Verdana","sans-serif";color:#999999'><hr size=2 width=420 style='width:315.0pt' align=left></span></div></div></div></div></div></div></div><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 <br>Level 9, 601 Bourke St, Melbourne Vic 3000<o:p></o:p></span></p><div><div><div><div><div><div><div class=MsoNormal><span style='font-size:9.0pt;font-family:"Verdana","sans-serif";color:#999999'><hr size=2 width=420 style='width:315.0pt' align=left></span></div></div></div></div></div></div></div><p class=MsoNormal><span style='font-size:9.0pt;font-family:"Verdana","sans-serif";color:#999999'><br>LISAsoft is part of the A2end Group of Companies<br></span><span style='font-size:9.0pt;font-family:"Verdana","sans-serif";color:#4F81BD'><a href="http://www.ardec.com.au/"><span style='color:#4F81BD;text-decoration:none'>http://www.ardec.com.au</span></a><br><a href="http://www.lisasoft.com/"><span style='color:#4F81BD;text-decoration:none'>http://www.lisasoft.com</span></a><br><a href="http://www.terrapages.com/"><span style='color:#4F81BD;text-decoration:none'>http://www.terrapages.com</span></a></span><o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>