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<p>Hi,</p>
<p>The WMS cache (which is used underneath by the WMTS driver)
writes each tiles in a separate file. So if you use
multi-threaded, as long as you read in parallel different
GDALDataset* object on the WMTS filename, and read disjoint areas,
that should be fine. There might be a slight risk of things going
bad if you happened to read the same tile from different
GDALDataset* object at the same time, as it could potentially read
a partially written cached tile, or concurrently write the tile in
the cache and corrupt it. The logic is in
frmts/wms/gdalwmscache.cpp<br>
</p>
<p>Even<br>
</p>
<div class="moz-cite-prefix">Le 29/05/2024 à 10:14, Michał Kowalczuk
via gdal-dev a écrit :<br>
</div>
<blockquote type="cite"
cite="mid:CAP+FqQByOka92rtC94P7+6yTLEK5aoSmcfPjxorHkx=AygPLoA@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="auto">Because this is not clear in documentation,
especially in WMTS driver docs, my question is strictly about
this issue to programmers who have already explored this topic.</div>
<div dir="auto"><br>
</div>
<div dir="auto">Regards</div>
<div dir="auto">Michal</div>
<div><br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">W dniu śr., 29.05.2024 o
10:04 Rahkonen Jukka <<a
href="mailto:jukka.rahkonen@maanmittauslaitos.fi"
moz-do-not-send="true" class="moz-txt-link-freetext">jukka.rahkonen@maanmittauslaitos.fi</a>>
napisał(a):<br>
</div>
<blockquote class="gmail_quote"
style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div link="blue" vlink="purple" style="word-wrap:break-word"
lang="FI">
<div class="m_4834396856744026984WordSection1">
<p class="MsoNormal"><span lang="EN-US">Hi,</span></p>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<p class="MsoNormal"><span lang="EN-US">No, I am not
sure because I do not program myself. Reading this
document
<a href="https://gdal.org/user/multithreading.html"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">https://gdal.org/user/multithreading.html</a>
makes me feel that it is possible to do some things
in parallel, but the programmer must know how to do
it right.</span></p>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<p class="MsoNormal"><span lang="EN-US">-Jukka Rahkonen-</span></p>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<div
style="border:none;border-top:solid #e1e1e1 1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span lang="EN-US">Lähettäjä:</span></b><span
lang="EN-US"> Javier Jimenez Shaw <<a
href="mailto:j1@jimenezshaw.com" target="_blank"
moz-do-not-send="true"
class="moz-txt-link-freetext">j1@jimenezshaw.com</a>>
<br>
<b>Lähetetty:</b> keskiviikko 29. toukokuuta 2024
10.41<br>
<b>Vastaanottaja:</b> Rahkonen Jukka <<a
href="mailto:jukka.rahkonen@maanmittauslaitos.fi" target="_blank"
moz-do-not-send="true"
class="moz-txt-link-freetext">jukka.rahkonen@maanmittauslaitos.fi</a>><br>
<b>Kopio:</b> Michał Kowalczuk <<a
href="mailto:michkowalczuk@gmail.com"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">michkowalczuk@gmail.com</a>>;
<a href="mailto:gdal-dev@lists.osgeo.org"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">gdal-dev@lists.osgeo.org</a><br>
<b>Aihe:</b> Re: [gdal-dev] GDAL WMTS get tiles no
documentation</span></p>
</div>
</div>
</div>
<div link="blue" vlink="purple" style="word-wrap:break-word"
lang="FI">
<div class="m_4834396856744026984WordSection1">
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<div>
<div>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
</div>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<div>
<div>
<p class="MsoNormal"><span lang="EN-US">On Wed, 29
May 2024 at 08:59, Rahkonen Jukka via gdal-dev
<</span><a
href="mailto:gdal-dev@lists.osgeo.org"
target="_blank" moz-do-not-send="true"><span
lang="EN-US">gdal-dev@lists.osgeo.org</span></a><span
lang="EN-US">> wrote:</span></p>
</div>
<blockquote
style="border:none;border-left:solid #cccccc 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-top:5.0pt;margin-right:0cm;margin-bottom:5.0pt">
<div>
<div>
<div>
<p class="MsoNormal"><span lang="EN-US">Hi,</span></p>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<p class="MsoNormal"><span lang="EN-US">When
you have a RasterBand from the WMTS
data source, it is abstracted and you
can read the raster data just like from
any other data source and raster band
</span><a
href="https://gdal.org/tutorials/raster_api_tut.html#reading-raster-data"
target="_blank" moz-do-not-send="true"><span
lang="EN-US">https://gdal.org/tutorials/raster_api_tut.html#reading-raster-data</span></a><span
lang="EN-US"> “There are a few ways to
read raster data, but the most common is
via the GDALRasterBand::RasterIO()
method. This method will automatically
take care of data type conversion,
up/down sampling and windowing.” GDAL
knows which tiles to read.</span></p>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<p class="MsoNormal"><span lang="EN-US">I do
not know if the WMTS driver can do
parallel tile downloads. If not, it is
possible to run many RasterIO() at the
same time, each reading data from a
different window like in this rasterio
document </span><a
href="https://rasterio.readthedocs.io/en/latest/topics/concurrency.html"
target="_blank" moz-do-not-send="true"><span
lang="EN-US">https://rasterio.readthedocs.io/en/latest/topics/concurrency.html</span></a><span
lang="EN-US">.</span></p>
</div>
</div>
</div>
</blockquote>
<div>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US">Jukka, are
you sure you can run several RasterIO in
parallel (on the same dataset)? in GDAL
GeoTIFF you cannot: the cache may be
corrupted. In that case I open several
datasets over the same file. I do not know
about WMTS.</span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
</div>
<blockquote
style="border:none;border-left:solid #cccccc 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-top:5.0pt;margin-right:0cm;margin-bottom:5.0pt">
<div>
<div>
<div>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<p class="MsoNormal"><span lang="EN-US">-Jukka
Rahkonen-</span></p>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<div
style="border:none;border-top:solid windowtext 1.0pt;padding:3.0pt 0cm 0cm 0cm;border-color:currentcolor currentcolor">
<p class="MsoNormal"><b><span lang="EN-US">Lähettäjä:</span></b><span
lang="EN-US"> gdal-dev <</span><a
href="mailto:gdal-dev-bounces@lists.osgeo.org" target="_blank"
moz-do-not-send="true"><span
lang="EN-US">gdal-dev-bounces@lists.osgeo.org</span></a><span
lang="EN-US">>
<b>Puolesta </b>Michal Kowalczuk via
gdal-dev<br>
<b>Lähetetty:</b> keskiviikko 29.
toukokuuta 2024 9.08<br>
<b>Vastaanottaja:</b> </span><a
href="mailto:gdal-dev@lists.osgeo.org"
target="_blank" moz-do-not-send="true"><span
lang="EN-US">gdal-dev@lists.osgeo.org</span></a><span
lang="EN-US"><br>
<b>Aihe:</b> [gdal-dev] GDAL WMTS get
tiles no documentation</span></p>
</div>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<div>
<p class="MsoNormal"><span lang="EN-US">Hi
GDAL fellows</span></p>
<div>
<p class="MsoNormal"><span lang="EN-US">This
is my first post on this mailing
list, so I'm asking for
understanding.</span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US">As
all we know the purpose of using
WMTS over WMS, I'd like to implement
parallel downloading tiles from
service using C API.</span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US">In
my opinion GDAL documentation (</span><a
href="https://gdal.org/drivers/raster/wmts.html" target="_blank"
moz-do-not-send="true"><span
lang="EN-US">https://gdal.org/drivers/raster/wmts.html</span></a><span
lang="EN-US">) says nothing on this
topic.</span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US">I
can get capabilities from WMTS, I
can open the selected subdataset but
how to get tiles for given extent? I
could not find any information how
to do it, even in the GDAL tests on
github.</span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US">I
am kindly asking for tips. It also
can be in python. How using pure
GDAL API fetch tiles to dynamically
complete the displayed map. This is
my goal.</span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US">Thank
you!</span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US">Michal</span></p>
</div>
</div>
</div>
</div>
<p class="MsoNormal"><span lang="EN-US">_______________________________________________<br>
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