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<div class="moz-cite-prefix">Hi Michael,</div>
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<div class="moz-cite-prefix">Here are some instructions to do
exactly what you are asking that I recently wrote for someone else
(you are not alone!):</div>
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<div class="moz-cite-prefix">The ESRI ASCII grid format is
supported by QGIS, and will load as a raster if you drag an .asc
file over the map canvas. The further complication with the
gridded dataset is that it is split into 10km tiles rather than
being a single national layer, so needs to be merged before
moving on to the next steps. This is fairly straightforward
using the following steps:</div>
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<div class="moz-cite-prefix">1. Unzip the downloaded data. You'll
notice that the 10km tile files are also zipped, and each placed
in a 100km square folder: hp\hp40_OST50GRID_20220506.zip</div>
<div class="moz-cite-prefix"><br>
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<div class="moz-cite-prefix">2. Move the zip files out of their
100km square folders to make it easier to process them all at
once. This can be done through File Explorer by searching in the
folder below the 100km square folders for *.zip<br>
</div>
<div class="moz-cite-prefix"><img src="cid:part1.Ds9Jfdeb.josg6blb@geodata.soton.ac.uk" alt=""></div>
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<div class="moz-cite-prefix">You should get 2858 results. Select
all of these files using Ctrl + A and then drag them into the
data folder - they will be moved out of their individual 100km
square folders</div>
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<div class="moz-cite-prefix">3. Unzip all the zip files. I don't
think that the built in Windows zip functionality can do this in
one go though. I use the open source 7zip software which allows
a bunch of zip files to be selected in File Explorer and then
from the right click menu, 'Extract Here' can be chosen. You
should now see a .asc file in the folder for each 10km grid
square, eg: HP40.asc. This is the grid data.</div>
<div class="moz-cite-prefix"><br>
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<div class="moz-cite-prefix">4. Merge the 10km tiles together.
This is done in QGIS using the Merge tool from the Processing
toolbox (or Raster > Miscellaneous > Merge...). In the
Input layers section, click the ellipsis button to open the file
selector, and use the 'Add File(s)...' button to add the .asc
files (if you sort by file type you can select them as a block).<br>
</div>
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<div class="moz-cite-prefix"><img src="cid:part2.wPfvD8X2.7Wj9VdLK@geodata.soton.ac.uk" alt=""></div>
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<div class="moz-cite-prefix">Fill out the rest of the Merge tool
dialog like this:</div>
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<div class="moz-cite-prefix"><img src="cid:part3.0wkqJ1hr.n10pcCQ6@geodata.soton.ac.uk" alt=""></div>
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<div class="moz-cite-prefix">Clicking Run will start the process,
which may take some time, but on completion you should have a
single national terrain dataset!</div>
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<div class="moz-cite-prefix">Cheers,</div>
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<div class="moz-cite-prefix">Andy<br>
</div>
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<div class="moz-cite-prefix">On 28/09/2022 12:32, Michael.Dodd via
Qgis-user wrote:<br>
</div>
<blockquote type="cite" cite="mid:LO2P265MB3406BEB29317C13BEE8A04D3B0549@LO2P265MB3406.GBRP265.PROD.OUTLOOK.COM">
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<p class="MsoNormal">I am trying to put together the 50m uk
DEM e.g. <a href="https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.data.gov.uk%2Fdataset%2F835cf20a-8feb-4394-8b30-dcfe840ac13d%2Fos-terrain-50-dtm&data=05%7C01%7Cajph%40geodata.soton.ac.uk%7C969a389b311348dc9ca508daa1452261%7C4a5378f929f44d3ebe89669d03ada9d8%7C0%7C0%7C637999615544988116%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=SJ5%2Fi079IPc9aBN9OHDgnKDMUVj0gyBQr3YNMxA%2FtfU%3D&reserved=0" originalsrc="https://www.data.gov.uk/dataset/835cf20a-8feb-4394-8b30-dcfe840ac13d/os-terrain-50-dtm" shash="ra4Ivi/i6nw9ZrAMsoAXrEDlTIXy/r/jvqzGe64hKlV621tlUaP4c74bLje7TS5fNocN6Y8/hwTY3Ugc/tpens7LpPKQBPkq1PKl8In9YeJ+tJowWbCzhS+r2CuiYWvMUccODAaCO5EGQFTxNcizavVnXqLIj2MjM4EP+iJLwWI=" moz-do-not-send="true">
https://www.data.gov.uk/dataset/835cf20a-8feb-4394-8b30-dcfe840ac13d/os-terrain-50-dtm</a>
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></p>
<p class="MsoNormal">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></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<pre class="moz-signature" cols="72">--
Andy Harfoot
Skype: gdi_ajph
Teams: <a class="moz-txt-link-abbreviated" href="mailto:ajph@soton.ac.uk">ajph@soton.ac.uk</a>
GeoData Institute
University of Southampton
Southampton
SO17 1BJ
<a class="moz-txt-link-abbreviated" href="http://www.geodata.soton.ac.uk">www.geodata.soton.ac.uk</a></pre>
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