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</o:shapelayout></xml><![endif]--></head><body lang=EN-GB link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Hi Roger<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Thanks for your comments. Much appreciated!<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Chris<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><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"'> Roger André [mailto:randre@gmail.com] <br><b>Sent:</b> 14 November 2011 21:50<br><b>To:</b> Chris Green<br><b>Cc:</b> tech@wildintellect.com; qgis-user@lists.osgeo.org<br><b>Subject:</b> Re: [Qgis-user] Simplify?<o:p></o:p></span></p></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>GRASS has some very good line simplification options which I believe can be accessed from within QGis. I like to run a light Douglas Peucker simplification to cut the vertice count down without dramatically altering the appearance of the data, followed by Lang simplification to generalize the appearance of things. A good description of the difference between these algorithms can be found at <a href="http://psimpl.sourceforge.net/douglas-peucker.html">http://psimpl.sourceforge.net/douglas-peucker.html</a> and <a href="http://psimpl.sourceforge.net/lang.html">http://psimpl.sourceforge.net/lang.html</a>.<o:p></o:p></p><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>BTW, using a vary small threshold tolerance with Douglas Peucker is a great way to remove vertices in a straight-line segments. For example, running a tolerance of .0015 on a set of fairly complex world country borders in GRASS yields the following for me:<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal> Number of vertices was reduced from 606998 to 230824<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>This pruning is not discernible against the original data set until about 1.250000 map scale. At 1:50000 it starts to look a little blocky.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>MapShaper is a great tool, and by doing a pruning of your excess vertices as metioned above, it might put the data under the 80 MB limit and allow you to use it.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Roger<o:p></o:p></p></div><div><p class=MsoNormal>--<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-bottom:12.0pt'><o:p> </o:p></p><div><p class=MsoNormal>On Mon, Nov 14, 2011 at 1:40 AM, Chris Green <<a href="mailto:chris.green@ibstv.co.uk">chris.green@ibstv.co.uk</a>> wrote:<o:p></o:p></p><p class=MsoNormal>Hi Alex<br><br>Thanks for your response. I have tried Mapshaper on smaller shp files, it is pretty good but it has a limit of 80M and some of my files are too large for this.<br><br>I would still very much like to get the Simplify function working. I assume from your comments that in general the QGIS Simplify function works fine so either I am doing something wrong, or there is a problem with my local copy of QGIS which I could resolve be re-installing?<br><br>By the way I can't find the DPSimplify plugin, any idea where I might find it?<br><br><br>Chris<br><br><br>-----Original Message-----<br>From: <a href="mailto:qgis-user-bounces@lists.osgeo.org">qgis-user-bounces@lists.osgeo.org</a> [mailto:<a href="mailto:qgis-user-bounces@lists.osgeo.org">qgis-user-bounces@lists.osgeo.org</a>] On Behalf Of Alex Mandel<br>Sent: 11 November 2011 20:27<br>To: <a href="mailto:qgis-user@lists.osgeo.org">qgis-user@lists.osgeo.org</a><br>Subject: Re: [Qgis-user] Simplify?<br><br>I see at least 3 tools in QGIS to do simply.<br>The one you mentioned in the vector menu (part of ftools)<br>The DPSimplify plugin (appears to be the precursor to the above tool)<br>and the Simply function in the vector editor<br><br>Of those the last one is the one I've used the most but operates on<br>individual features at a time. The key question I can see for all of<br>them though is what tolerance are you setting and what projection is<br>your data in since this determines the units for tolerance.<br><br>I just tested with a tolerance of 1 on a GCS Lat/Lon WGS84 dataset of<br>lines and it seemed to work fine, I imagine if I had left the tolerance<br>at 0.0001 it would have done nothing.<br><br>Worst case scenario mapshaper is an online tool just for this.<br><br>Enjoy,<br>Alex<br><br><br>On 11/11/2011 05:39 AM, Chris Green wrote:<br>> Hi Ramon<br>><br>><br>><br>> I have been trying to modify the original shape file rather than save to a new file. When I tried selecting the ‘save to a new file’ option , the message after simplification said<br>><br>><br>><br>> ‘There were 3638321 vertices in original dataset which were reduced to 3638321 vertices after simplification’<br>><br>><br>><br>> In other words, no simplification at all. I suspect that this is actually what is happening when I try to over-write the existing file – it indicates that simplification took place but actually what is saved is identical to the original.<br>><br>><br>><br>> Thanks anyway…..<br>><br>><br>><br>><br>><br>> Chris<br>><br>><br>><br>> From: <a href="mailto:qgis-user-bounces@lists.osgeo.org">qgis-user-bounces@lists.osgeo.org</a> [mailto:<a href="mailto:qgis-user-bounces@lists.osgeo.org">qgis-user-bounces@lists.osgeo.org</a>] On Behalf Of Ramon Andiñach<br>> Sent: 11 November 2011 13:19<br>> To: <<a href="mailto:qgis-user@lists.osgeo.org">qgis-user@lists.osgeo.org</a>><br>> Subject: Re: [Qgis-user] Simplify?<br>><br>><br>><br>><br>><br>> On 11/11/2011, at 20:40, "Chris Green" <<a href="mailto:chris.green@ibstv.co.uk">chris.green@ibstv.co.uk</a>> wrote:<br>><br>> Hello<br>><br>><br>><br>> I am using QGIS 1.7 in a Windows 7 environment. Everything seems great except for the simplify function (Vector->Geometry Tools->Simplify Geometries)<br>><br>><br>><br>> I am trying to simplify an ESRI shape file which is around 95M. I have tried various tolerance settings, but although it looks like some simplification is taking place, actually the file is unchanged. So for example with tolerance setting of 1.0 I get an encouraging message that says:<br>><br>><br>><br>> ‘There were 3638321 vertices in original dataset which were reduced to 559351 vertices after simplification’<br>><br>><br>><br>> However after saving the changes to the layer, the dataset still looks identical to the un-simplified version and the file size remains unchanged at 95M. I have tried to simplify smaller shape files also, but with the same result.<br>><br>><br>><br>> Can someone tell me what I am I doing wrong?<br>><br>><br>><br>><br>><br>> Hi Chris,<br>><br>> This is a guess...<br>><br>><br>><br>> I suppose your output file is different to your input file?<br>><br>><br>><br>> (otherwise windows will probably get confused)<br>><br>><br>><br>> -ramon.<br>><br><br><br>_______________________________________________<br>Qgis-user mailing list<br><a href="mailto:Qgis-user@lists.osgeo.org">Qgis-user@lists.osgeo.org</a><br><a href="http://lists.osgeo.org/mailman/listinfo/qgis-user" target="_blank">http://lists.osgeo.org/mailman/listinfo/qgis-user</a><br><br><br>_______________________________________________<br>Qgis-user mailing list<br><a href="mailto:Qgis-user@lists.osgeo.org">Qgis-user@lists.osgeo.org</a><br><a href="http://lists.osgeo.org/mailman/listinfo/qgis-user" target="_blank">http://lists.osgeo.org/mailman/listinfo/qgis-user</a><o:p></o:p></p></div><p class=MsoNormal><o:p> </o:p></p></div></div></body></html>