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<p class="MsoNormal"><span style="color:#1F497D">The world files are read internally by GDAL, not MapServer. I wonder if there’s a way to test this just using GDAL and take MapServer out of the equation completely. Is there any projection being done? That could
also be a source of slivers. Is it possible to generate the tiles with just a bit of overlap?<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">Steve<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> mapserver-users-bounces@lists.osgeo.org [mailto:mapserver-users-bounces@lists.osgeo.org]
<b>On Behalf Of </b>Lars I. Nielsen<br>
<b>Sent:</b> Thursday, June 12, 2014 9:02 AM<br>
<b>To:</b> mapserver-users@lists.osgeo.org<br>
<b>Subject:</b> [mapserver-users] TileIndex - accuracy and truncation ?<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hi,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">For performance reasons, I've (used FME to) split a large PNG into 450 small tiles, serving them with a Mapserver tileindex as a WMS service to a web solution.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Howeever, white lines appear between some of the tile rows (not all) at some scales (not all).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I've looked deeper into the WLD files for the individual tiles, and found that the calculations are accurate to 1/10 of a nanometer. At least if one uses all 10 decimals.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Tiles are 2254 pixels high, and (as per the WLDs below) 6138899.3169212583 - 0.0204375000 * 2254 = 6138853.2507962583 (almost equal to 6138853.2507962584)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Which leads me to suspect that some sort of truncation goes on, yielding some sort of rounding error.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Do anyone know whether the tileindex calculations truncates any of the values in the WLD files ? And if so, by how much ?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Cheers.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">--<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">A typical map picture with a white line can be seen via this link:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><a href="http://hvmgo01.hvenegaard.dk/mswms/mapserv.exe?map=odensekkgd_wms.map&LAYERS=ASSISTENS&TRANSPARENT=true&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&STYLES=&FORMAT=image/png&SRS=epsg:25832&BBOX=586609.80952408,6138781.1015875,586686.0222225,6138857.3142859&WIDTH=256&HEIGHT=256">http://hvmgo01.hvenegaard.dk/mswms/mapserv.exe?map=odensekkgd_wms.map&LAYERS=ASSISTENS&TRANSPARENT=true&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&STYLES=&FORMAT=image/png&SRS=epsg:25832&BBOX=586609.80952408,6138781.1015875,586686.0222225,6138857.3142859&WIDTH=256&HEIGHT=256</a><o:p></o:p></p>
<p class="MsoNormal">Here's the WLD of the two tiles displayed in the picture:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Upper tile WLD:<o:p></o:p></p>
<p class="MsoNormal">0.0204375000<o:p></o:p></p>
<p class="MsoNormal">0.0000000000<o:p></o:p></p>
<p class="MsoNormal">0.0000000000<o:p></o:p></p>
<p class="MsoNormal">-0.0204375000<o:p></o:p></p>
<p class="MsoNormal">586620.6934394070<o:p></o:p></p>
<p class="MsoNormal">6138899.3169212583<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Lower tile WLD:<o:p></o:p></p>
<p class="MsoNormal">0.0204375000<o:p></o:p></p>
<p class="MsoNormal">0.0000000000<o:p></o:p></p>
<p class="MsoNormal">0.0000000000<o:p></o:p></p>
<p class="MsoNormal">-0.0204375000<o:p></o:p></p>
<p class="MsoNormal">586620.6934394070<o:p></o:p></p>
<p class="MsoNormal">6138853.2507962584<o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:DA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:DA">--<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:DA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:DA">Ps! As I wrote previously, I'm using FME to create the tiles. So I have little control over the actual coordinate and pixel values, and only specify the number of tiles I need. So manual
truncation is not really a viable option.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:DA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:DA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:DA">Kind regards / Med venlig hilsen<br>
Lars I. Nielsen<br>
----------------------------------------------------------------<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="DA" style="color:#1F497D;mso-fareast-language:DA">Landinspektør, Senior GIS Programmør og Konsulent<br>
Hvenegaard Landinspektører A/S<br>
Rugaardsvej 55, DK-5000 Odense C<br>
Denmark<br>
Tel. +45 6313 5050<br>
<a href="http://www.hvenegaard.dk/">http://www.hvenegaard.dk</a><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="DA"><o:p> </o:p></span></p>
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