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<p class="MsoNormal"><span style="color:#1F497D">Hi, <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">So the underlying data might not be very efficient, for example, no internal Tiling, or compressions used.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">What I would suggest is…<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="color:#1F497D"><span style="mso-list:Ignore">1.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="color:#1F497D">Create a VRT of all the data you have.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="color:#1F497D"><span style="mso-list:Ignore">2.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="color:#1F497D">Using GDAL Translate convert the VRT into a GeoTiff, with the following<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="color:#1F497D"><span style="mso-list:Ignore">a.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="color:#1F497D">NoData Value of -9999<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="color:#1F497D"><span style="mso-list:Ignore">b.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="color:#1F497D">Advanced Parameters<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:108.0pt;text-indent:-108.0pt;mso-text-indent-alt:-9.0pt;mso-list:l0 level3 lfo1">
<![if !supportLists]><span style="color:#1F497D"><span style="mso-list:Ignore"><span style="font:7.0pt "Times New Roman"">
</span>i.<span style="font:7.0pt "Times New Roman""> </span></span></span><![endif]><span style="color:#1F497D">NUM_THREADS = ALL_CPUS<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:108.0pt;text-indent:-108.0pt;mso-text-indent-alt:-9.0pt;mso-list:l0 level3 lfo1">
<![if !supportLists]><span style="color:#1F497D"><span style="mso-list:Ignore"><span style="font:7.0pt "Times New Roman"">
</span>ii.<span style="font:7.0pt "Times New Roman""> </span></span></span><![endif]><span style="color:#1F497D">BIGTIFF = YES<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:108.0pt;text-indent:-108.0pt;mso-text-indent-alt:-9.0pt;mso-list:l0 level3 lfo1">
<![if !supportLists]><span style="color:#1F497D"><span style="mso-list:Ignore"><span style="font:7.0pt "Times New Roman"">
</span>iii.<span style="font:7.0pt "Times New Roman""> </span></span></span><![endif]><span style="color:#1F497D">TILED = YES<o:p></o:p></span></p>
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<![if !supportLists]><span style="color:#1F497D"><span style="mso-list:Ignore"><span style="font:7.0pt "Times New Roman"">
</span>iv.<span style="font:7.0pt "Times New Roman""> </span></span></span><![endif]><span style="color:#1F497D">COMPRESS = LZW<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="color:#1F497D"><span style="mso-list:Ignore">c.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="color:#1F497D">Data Type to Float32<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="color:#1F497D"><span style="mso-list:Ignore">3.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="color:#1F497D">You can then also use Pyramids for your Maximum zoom levels, I recommend external, as they can be deleted if you want to change them.<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">I hope that goes some wat to helping.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Kind Regards,<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">Richard.<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"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="mso-fareast-language:EN-IE">From:</span></b><span lang="EN-US" style="mso-fareast-language:EN-IE"> Qgis-user <qgis-user-bounces@lists.osgeo.org>
<b>On Behalf Of </b>Michael.Dodd via Qgis-user<br>
<b>Sent:</b> 28 September 2022 12:32<br>
<b>To:</b> 'qgis-user@lists.osgeo.org' <qgis-user@lists.osgeo.org><br>
<b>Subject:</b> [Qgis-user] large DEM not loading tiles correctly<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span lang="EN-GB">I am trying to put together the 50m uk DEM e.g.
</span><a href="https://www.data.gov.uk/dataset/835cf20a-8feb-4394-8b30-dcfe840ac13d/os-terrain-50-dtm"><span lang="EN-GB">https://www.data.gov.uk/dataset/835cf20a-8feb-4394-8b30-dcfe840ac13d/os-terrain-50-dtm</span></a><span lang="EN-GB"> but it often does
not work. The data are supplied as thousands of small tiles that takes ages to unpack and put into a folder to get into qgis, however when you try to load the tiles some work and others don’t and even the ones that do work and display fine sometimes don’t
merge to form large tiles and sometimes will form virtual rasters but not merged files. Basically it is a mess. I suspect others have done this successfully so any suggestions?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">It is particularly odd that some of the tiles will merge and others won’t and that some won’t display if you ask it to load hundreds at a time but if you just add them in a few at a time then they will load and display
(in addition to the hundreds already loaded). This suggests various bugs assuming the original data are not in a whole variety of slightly different formats (should all be .asc)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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