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aria-hidden="true"></span> Previous</a> + <a href="operations_computation.html" class="btn btn-neutral float-right" title="Computation of coordinate operations between two CRS" accesskey="n">Next <span class="fa fa-arrow-circle-right" aria-hidden="true"></span></a> + </div> + <hr/> +</div> + <div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article"> + <div itemprop="articleBody"> + + <section id="the-pipeline-operator"> +<span id="pipeline"></span><h1>The pipeline operator<a class="headerlink" href="#the-pipeline-operator" title="Permalink to this headline">¶</a></h1> +<div class="versionadded"> +<p><span class="versionmodified added">New in version 5.0.0.</span></p> +</div> +<p>Construct complex operations by daisy-chaining operations in a sequential pipeline.</p> +<table class="docutils align-default"> +<colgroup> +<col style="width: 20%" /> +<col style="width: 80%" /> +</colgroup> +<tbody> +<tr class="row-odd"><td><p><strong>Alias</strong></p></td> +<td><p>pipeline</p></td> +</tr> +<tr class="row-even"><td><p><strong>Domain</strong></p></td> +<td><p>2D, 3D and 4D</p></td> +</tr> +<tr class="row-odd"><td><p><strong>Input type</strong></p></td> +<td><p>Any</p></td> +</tr> +<tr class="row-even"><td><p><strong>Output type</strong></p></td> +<td><p>Any</p></td> +</tr> +</tbody> +</table> +<div class="admonition note"> +<p class="admonition-title">Note</p> +<p>See the section on <a class="reference internal" href="../usage/transformation.html#transformation"><span class="std std-ref">Geodetic transformation</span></a> for a more thorough introduction +to the concept of transformation pipelines in PROJ.</p> +</div> +<p>With the pipeline operation it is possible to perform several operations after each +other on the same input data. This feature makes it possible to create transformations +that are made up of more than one operation, e.g. performing a datum shift and then +applying a suitable map projection. Theoretically any transformation between two +coordinate reference systems is possible to perform using the pipeline operation, +provided that the necessary coordinate operations in each step is available in PROJ.</p> +<p>A pipeline is made up of a number of steps, with each step being a coordinate operation +in itself. By connecting these individual steps sequentially we end up with a concatenated +coordinate operation. An example of this is a transformation from geodetic coordinates +on the GRS80 ellipsoid to a projected system where the east-west and north-east axes has +been swapped:</p> +<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>+proj=pipeline +ellps=GRS80 +step +proj=merc +step +proj=axisswap +order=2,1 +</pre></div> +</div> +<p>Here the first step is applying the <a class="reference internal" href="projections/merc.html#merc"><span class="std std-ref">Mercator</span></a> projection and the second step is +applying the <a class="reference internal" href="conversions/axisswap.html#axisswap"><span class="std std-ref">Axis swap</span></a> conversion. Note that the <cite>+ellps=GRS80</cite> is specified +before the first occurrence of <cite>+step</cite>. This means that the GRS80 ellipsoid is used +in both steps, since any parameter stated before the first occurrence of <cite>+step</cite> is +treated as a global parameter and is transferred to each individual steps.</p> +<section id="rules-for-pipelines"> +<h2>Rules for pipelines<a class="headerlink" href="#rules-for-pipelines" title="Permalink to this headline">¶</a></h2> +<p><strong>1. Pipelines must consist of at least one step.</strong></p> +<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>+proj=pipeline +</pre></div> +</div> +<p>Will result in an error.</p> +<p><strong>2. Pipelines can only be nested if the nested pipeline is defined in an init file.</strong></p> +<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>+proj=pipeline ++step +proj=pipeline +step +proj=merc +step +proj=axisswap +order=2,1 ++step +proj=unitconvert +xy_in=m +xy_out=us-ft +</pre></div> +</div> +<p>Results in an error, while</p> +<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>+proj=pipeline ++step +init=predefined_pipelines:projectandswap ++step +proj=unitconvert +xy_in=m +xy_out=us-ft +</pre></div> +</div> +<p>does not.</p> +<p><strong>3. Pipelines without a forward path can’t be constructed.</strong></p> +<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>+proj=pipeline +step +inv +proj=urm5 +</pre></div> +</div> +<p>Will result in an error since <a class="reference internal" href="projections/urm5.html#urm5"><span class="std std-ref">Urmaev V</span></a> does not have an inverse operation defined.</p> +<p id="global-pipeline-parameter"><strong>4. Parameters added before the first `+step` are global and will be applied to all steps.</strong></p> +<p>In the following the GRS80 ellipsoid will be applied to all steps.</p> +<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>+proj=pipeline +ellps=GRS80 ++step +proj=cart ++step +proj=helmert +x=10 +y=3 +z=1 ++step +proj=cart +inv ++step +proj=merc +</pre></div> +</div> +<p><strong>5. Units of operations must match between steps.</strong></p> +<div class="versionadded"> +<p><span class="versionmodified added">New in version 5.1.0.</span></p> +</div> +<p>The output units of step <em>n</em> must match the expected input unit of step <em>n+1</em>. E.g., you can’t +pass an operation that outputs projected coordinates to an operation that expects angular units +(degrees). An example of such a unit mismatch is displayed below.</p> +<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>+proj=pipeline ++step +proj=merc # Mercator outputs projected coordinates ++step +proj=robin # The Robinson projection expects angular input +</pre></div> +</div> +</section> +<section id="parameters"> +<h2>Parameters<a class="headerlink" href="#parameters" title="Permalink to this headline">¶</a></h2> +<section id="required"> +<h3>Required<a class="headerlink" href="#required" title="Permalink to this headline">¶</a></h3> +<dl class="std option"> +<dt class="sig sig-object std" id="cmdoption-arg-step"> +<span class="sig-name descname"><span class="pre">+step</span></span><span class="sig-prename descclassname"></span><a class="headerlink" href="#cmdoption-arg-step" title="Permalink to this definition">¶</a></dt> +<dd><p>Separate each step in a pipeline.</p> +</dd></dl> + +</section> +<section id="optional"> +<h3>Optional<a class="headerlink" href="#optional" title="Permalink to this headline">¶</a></h3> +<dl class="std option"> +<dt class="sig sig-object std" id="cmdoption-arg-inv"> +<span class="sig-name descname"><span class="pre">+inv</span></span><span class="sig-prename descclassname"></span><a class="headerlink" href="#cmdoption-arg-inv" title="Permalink to this definition">¶</a></dt> +<dd><p>Invert a step in a pipeline.</p> +</dd></dl> + +<dl class="std option"> +<dt class="sig sig-object std" id="cmdoption-arg-omit_fwd"> +<span id="cmdoption-arg-omit-fwd"></span><span class="sig-name descname"><span class="pre">+omit_fwd</span></span><span class="sig-prename descclassname"></span><a class="headerlink" href="#cmdoption-arg-omit_fwd" title="Permalink to this definition">¶</a></dt> +<dd><div class="versionadded"> +<p><span class="versionmodified added">New in version 6.3.0.</span></p> +</div> +<p>Skip a step of the pipeline when it is followed in the forward path.</p> +<p>The following example shows a combined use of <a class="reference internal" href="conversions/push.html#push"><span class="std std-ref">push</span></a> and <a class="reference internal" href="conversions/pop.html#pop"><span class="std std-ref">pop</span></a> operators, +with <code class="docutils literal notranslate"><span class="pre">omit_fwd</span></code> and <code class="docutils literal notranslate"><span class="pre">omit_inv</span></code> options, to implement a vertical adjustment that must +be done in a interpolation CRS that is different from the horizontal CRS +used in input and output. +omit_fwd in the forward path avoid a useless +inverse horizontal transformation and relies on the pop operator to restore +initial horizontal coordinates. +omit_inv serves the similar purpose when +the pipeline is executed in the reverse direction</p> +<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>+proj=pipeline ++step +proj=unitconvert +xy_in=deg +xy_out=rad ++step +proj=push +v_1 +v_2 ++step +proj=hgridshift +grids=nvhpgn.gsb +omit_inv ++step +proj=vgridshift +grids=g1999u05.gtx +multiplier=1 ++step +inv +proj=hgridshift +grids=nvhpgn.gsb +omit_fwd ++step +proj=pop +v_1 +v_2 ++step +proj=unitconvert +xy_in=rad +xy_out=deg +</pre></div> +</div> +</dd></dl> + +<dl class="std option"> +<dt class="sig sig-object std" id="cmdoption-arg-omit_inv"> +<span id="cmdoption-arg-omit-inv"></span><span class="sig-name descname"><span class="pre">+omit_inv</span></span><span class="sig-prename descclassname"></span><a class="headerlink" href="#cmdoption-arg-omit_inv" title="Permalink to this definition">¶</a></dt> +<dd><div class="versionadded"> +<p><span class="versionmodified added">New in version 6.3.0.</span></p> +</div> +<p>Skip a step of the pipeline when it is followed in the reverse path.</p> +</dd></dl> + +</section> +</section> +</section> + + + </div> + </div> + <footer><div class="rst-footer-buttons" role="navigation" aria-label="Footer"> + <a href="transformations/xyzgridshift.html" class="btn btn-neutral float-left" title="Geocentric grid shift" accesskey="p" rel="prev"><span class="fa fa-arrow-circle-left" aria-hidden="true"></span> Previous</a> + <a href="operations_computation.html" class="btn btn-neutral float-right" title="Computation of coordinate operations between two CRS" accesskey="n" rel="next">Next <span class="fa fa-arrow-circle-right" aria-hidden="true"></span></a> + </div> + + <hr/> + + <div role="contentinfo"> + <p>© Copyright 1983-2022. + <span class="lastupdated">Last updated on 22 Mar 2022. + </span></p> + </div> + + Built with <a href="https://www.sphinx-doc.org/">Sphinx</a> using a + <a href="https://github.com/readthedocs/sphinx_rtd_theme">theme</a> + provided by <a href="https://readthedocs.org">Read the Docs</a>. + + +</footer> + </div> + </div> + </section> + </div> + <script> + jQuery(function () { + SphinxRtdTheme.Navigation.enable(true); + }); + </script> + +</body> +</html>
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