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<section id="network-capabilities">
<span id="network"></span><h1>Network capabilities<a class="headerlink" href="#network-capabilities" title="Permalink to this headline">¶</a></h1>
<div class="versionadded">
<p><span class="versionmodified added">New in version 7.0.</span></p>
</div>
<p>PROJ 7.0 has introduced, per <a class="reference internal" href="../community/rfc/rfc-4.html#rfc4"><span class="std std-ref">PROJ RFC 4: Remote access to grids and GeoTIFF grids</span></a>, the capability to work with grid files
that are not installed on the local machine where PROJ is executed.</p>
<p>This enables to transparently download the parts of grids that are needed to
perform a coordinate transformation.</p>
<section id="cdn-of-geotiff-grids">
<span id="cdn-grids"></span><h2>CDN of GeoTIFF grids<a class="headerlink" href="#cdn-of-geotiff-grids" title="Permalink to this headline">¶</a></h2>
<p>Files are accessed by default through a CDN (Content Delivery Network),
accessible through <a class="reference external" href="https://cdn.proj.org">https://cdn.proj.org</a>, that contains <a class="reference internal" href="../specifications/geodetictiffgrids.html#geodetictiffgrids"><span class="std std-ref">Geodetic TIFF grids (GTG)</span></a>
datasets which are mirrored and managed by the
<a class="reference external" href="https://github.com/OSGeo/PROJ-data/">https://github.com/OSGeo/PROJ-data/</a> GitHub project.
Files in the CDN are designed to be used by PROJ 7 or later, but any software
project wishing to use the CDN for shifting support are encouraged to
participate in the project and leverage the CDN.</p>
</section>
<section id="how-to-enable-network-capabilities">
<h2>How to enable network capabilities ?<a class="headerlink" href="#how-to-enable-network-capabilities" title="Permalink to this headline">¶</a></h2>
<p>This capability assumes that PROJ has been build against <cite>libcurl</cite>, and that
the user authorizes network access.</p>
<p>Authorizing network access can be done in multiple ways:</p>
<blockquote>
<div><ul class="simple">
<li><p>enabling / uncommenting the <code class="docutils literal notranslate"><span class="pre">network</span> <span class="pre">=</span> <span class="pre">on</span></code> line of <a class="reference internal" href="../resource_files.html#proj-ini"><span class="std std-ref">proj.ini</span></a></p></li>
<li><p>defining the <span class="target" id="index-0"></span><a class="reference internal" href="environmentvars.html#envvar-PROJ_NETWORK"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PROJ_NETWORK</span></code></a> environment variable to ON</p></li>
<li><p>or using the <code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">proj_context_set_enable_network()</span></code> with a
<code class="docutils literal notranslate"><span class="pre">enabled</span> <span class="pre">=</span> <span class="pre">TRUE</span></code> value.</p></li>
</ul>
</div></blockquote>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Instead of using the <cite>libcurl</cite> implementation, an application using the PROJ
API can supply its own network implementation through C function callbacks
with <code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">proj_context_set_network_callbacks()</span></code>. Enabling network use
must still be done with one of the above mentioned method.</p>
</div>
</section>
<section id="setting-endpoint">
<h2>Setting endpoint<a class="headerlink" href="#setting-endpoint" title="Permalink to this headline">¶</a></h2>
<p>When this is enabled, and a grid is not found in the various locations where
<a class="reference internal" href="../resource_files.html#resource-file-paths"><span class="std std-ref">resource files are looked for</span></a>, PROJ will then
attempt at loading the file from a remote server, which defaults to
<a class="reference external" href="https://cdn.proj.org">https://cdn.proj.org</a> in <a class="reference internal" href="../resource_files.html#proj-ini"><span class="std std-ref">proj.ini</span></a>. This location can be changed with
the <span class="target" id="index-1"></span><a class="reference internal" href="environmentvars.html#envvar-PROJ_NETWORK_ENDPOINT"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PROJ_NETWORK_ENDPOINT</span></code></a> environment variable or with
<code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">proj_context_set_url_endpoint()</span></code>.</p>
</section>
<section id="caching">
<h2>Caching<a class="headerlink" href="#caching" title="Permalink to this headline">¶</a></h2>
<p>To avoid repeated access to network, a local cache of downloaded chunks of grids
is implemented as SQLite3 database, <code class="file docutils literal notranslate"><span class="pre">cache.db</span></code>, stored in the
<a class="reference internal" href="../resource_files.html#user-writable-directory"><span class="std std-ref">PROJ user writable directory</span></a>.</p>
<p>This local caching is enabled by default (can be changed in <a class="reference internal" href="../resource_files.html#proj-ini"><span class="std std-ref">proj.ini</span></a> or
with <code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">proj_grid_cache_set_enable()</span></code>). The default maximum size of the
cache is 300 MB, which is more than half of the total size of grids available,
at time of writing. This size can also be customized in <a class="reference internal" href="../resource_files.html#proj-ini"><span class="std std-ref">proj.ini</span></a> or
with <code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">proj_grid_cache_set_max_size()</span></code></p>
</section>
<section id="download-api">
<h2>Download API<a class="headerlink" href="#download-api" title="Permalink to this headline">¶</a></h2>
<p>When on-demand loading of grid is not desirable, the PROJ API also offers the
capability to download whole grids in the
<a class="reference internal" href="../resource_files.html#user-writable-directory"><span class="std std-ref">PROJ user writable directory</span></a> by using the
<code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">proj_is_download_needed()</span></code> and <code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">proj_download_file()</span></code> functions.</p>
</section>
<section id="download-utility">
<h2>Download utility<a class="headerlink" href="#download-utility" title="Permalink to this headline">¶</a></h2>
<p><a class="reference internal" href="../apps/projsync.html#projsync"><span class="std std-ref">projsync</span></a> is a tool for downloading resource files.</p>
</section>
<section id="mirroring">
<h2>Mirroring<a class="headerlink" href="#mirroring" title="Permalink to this headline">¶</a></h2>
<p>If you are able, you are encouraged to mirror the grids via AWS S3 command line:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>aws s3 sync s3://cdn.proj.org .
</pre></div>
</div>
<p>If direct S3 access is not possible, you can also use wget to locally mirror the
data:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>wget --mirror https://cdn.proj.org/
</pre></div>
</div>
</section>
<section id="acknowledgments">
<h2>Acknowledgments<a class="headerlink" href="#acknowledgments" title="Permalink to this headline">¶</a></h2>
<p>The s3://cdn.proj.org bucket is hosted by the
<a class="reference external" href="https://aws.amazon.com/opendata/public-datasets/">Amazon Public Datasets program</a>.
CDN services are provided by the AWS Public Dataset team via
<a class="reference external" href="https://aws.amazon.com/cloudfront/">CloudFront</a></p>
</section>
</section>
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