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shift</li> + <li class="wy-breadcrumbs-aside"> + <a href="https://github.com/OSGeo/PROJ/edit/8.2/docs/source/operations/transformations/hgridshift.rst" class="fa fa-github"> Edit on GitHub</a> + </li> + </ul><div class="rst-breadcrumbs-buttons" role="navigation" aria-label="Sequential page navigation"> + <a href="molobadekas.html" class="btn btn-neutral float-left" title="Molodensky-Badekas transform" accesskey="p"><span class="fa fa-arrow-circle-left" aria-hidden="true"></span> Previous</a> + <a href="tinshift.html" class="btn btn-neutral float-right" title="Triangulated Irregular Network based transformation" 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="horizontal-grid-shift"> +<span id="hgridshift"></span><h1>Horizontal grid shift<a class="headerlink" href="#horizontal-grid-shift" 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>Change of horizontal datum by grid shift.</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>hgridshift</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>Geodetic coordinates (horizontal), meters (vertical), +decimalyear (temporal)</p></td> +</tr> +<tr class="row-even"><td><p><strong>Output type</strong></p></td> +<td><p>Geodetic coordinates (horizontal), meters (vertical), +decimalyear (temporal)</p></td> +</tr> +</tbody> +</table> +<p>The horizontal grid shift is done by offsetting the planar input coordinates by +a specific amount determined by the loaded grids. The simplest use case of the +horizontal grid shift is applying a single grid:</p> +<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>+proj=hgridshift +grids=nzgr2kgrid0005.gsb +</pre></div> +</div> +<p>More than one grid can be loaded at the same time, for instance in case the +dataset needs to be transformed spans several countries. In this example grids +of the continental US, Alaska and Canada is loaded at the same time:</p> +<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>+proj=hgridshift +grids=@conus,@alaska,@ntv2_0.gsb,@ntv_can.dat +</pre></div> +</div> +<p>The <code class="docutils literal notranslate"><span class="pre">@</span></code> in the above example states that the grid is optional, in case the grid +is not found in the PROJ search path. The list of grids is prioritized so that +grids in the start of the list takes precedence over the grids in the back of the +list.</p> +<p>PROJ supports CTable2, NTv1 and NTv2 files for horizontal grid corrections. Details +about all three formats can be found in the GDAL documentation and/or driver source +code. GDAL reads and writes all three formats. Using GDAL for construction of +new grids is recommended.</p> +<section id="temporal-gridshifting"> +<h2>Temporal gridshifting<a class="headerlink" href="#temporal-gridshifting" title="Permalink to this headline">¶</a></h2> +<div class="versionadded"> +<p><span class="versionmodified added">New in version 5.1.0.</span></p> +</div> +<p>By initializing the horizontal gridshift operation with a central epoch, it can be +used as a step function applying the grid offsets only if a coordinate is +transformed from an epoch before grids central epoch to an epoch after. This is +handy in transformations where it is necessary to handle deformations caused by +seismic activity.</p> +<p>The central epoch of the grid is controlled with <a class="reference internal" href="vgridshift.html#cmdoption-arg-t_epoch"><code class="xref std std-option docutils literal notranslate"><span class="pre">+t_epoch</span></code></a> and the final +epoch of the coordinate is set with <a class="reference internal" href="vgridshift.html#cmdoption-arg-t_final"><code class="xref std std-option docutils literal notranslate"><span class="pre">+t_final</span></code></a>. The observation epoch of +the coordinate is part of the coordinate tuple.</p> +<p>Suppose we want to model the deformation of the 2008 earthquake in Iceland in +a transformation of data from 2005 to 2009:</p> +<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>echo 63.992 -21.014 10.0 2005.0 | cct +proj=hgridshift +grids=iceland2008.gsb +t_epoch=2008.4071 +t_final=2009.0 +63.9920021 -21.0140013 10.0 2005.0 +</pre></div> +</div> +<div class="admonition note"> +<p class="admonition-title">Note</p> +<p>The timestamp of the resulting coordinate is still 2005.0. The observation +time is always kept unchanged as it would otherwise be impossible to do the +inverse transformation.</p> +</div> +<p>Temporal gridshifting is especially powerful in transformation pipelines where +several gridshifts can be chained together, effectively acting as a series of +step functions that can be applied to a coordinate that is propagated through +time. In the following example we establish a pipeline that allows transformation +of coordinates from any given epoch up until the current date, applying only +those gridshifts that have central epochs between the observation epoch and +the final epoch:</p> +<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>+proj=pipeline +t_final=now ++step +proj=hgridshift +grids=earthquake_1.gsb +t_epoch=2010.421 ++step +proj=hgridshift +grids=earthquake_2.gsb +t_epoch=2013.853 ++step +proj=hgridshift +grids=earthquake_3.gsb +t_epoch=2017.713 +</pre></div> +</div> +<div class="admonition note"> +<p class="admonition-title">Note</p> +<p>The special epoch <em>now</em> is used when specifying the final epoch with +<a class="reference internal" href="vgridshift.html#cmdoption-arg-t_final"><code class="xref std std-option docutils literal notranslate"><span class="pre">+t_final</span></code></a>. This results in coordinates being transformed to the +current date. Additionally, <a class="reference internal" href="vgridshift.html#cmdoption-arg-t_final"><code class="xref std std-option docutils literal notranslate"><span class="pre">+t_final</span></code></a> is used as a +<a class="reference internal" href="../pipeline.html#global-pipeline-parameter"><span class="std std-ref">global pipeline parameter</span></a>, which means +that it is applied to all the steps in the pipeline.</p> +</div> +<p>In the above transformation, a coordinate with observation epoch 2009.32 would +be subject to all three gridshift steps in the pipeline. A coordinate with +observation epoch 2014.12 would only by offset by the last step in the pipeline.</p> +</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-grids"> +<span class="sig-name descname"><span class="pre">+grids</span></span><span class="sig-prename descclassname"><span class="pre">=<list></span></span><a class="headerlink" href="#cmdoption-arg-grids" title="Permalink to this definition">¶</a></dt> +<dd><p>Comma-separated list of grids to load. If a grid is prefixed by an <cite>@</cite> the +grid is considered optional and PROJ will the not complain if the grid is +not available.</p> +<p>Grids are expected to be in CTable2, NTv1 or NTv2 format.</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-t_epoch"> +<span id="cmdoption-arg-t-epoch"></span><span class="sig-name descname"><span class="pre">+t_epoch</span></span><span class="sig-prename descclassname"><span class="pre">=<time></span></span><a class="headerlink" href="#cmdoption-arg-t_epoch" title="Permalink to this definition">¶</a></dt> +<dd><p>Central epoch of the transformation.</p> +</dd></dl> + +<div class="versionadded"> +<p><span class="versionmodified added">New in version 5.1.0.</span></p> +</div> +<dl class="std option"> +<dt class="sig sig-object std" id="cmdoption-arg-t_final"> +<span id="cmdoption-arg-t-final"></span><span class="sig-name descname"><span class="pre">+t_final</span></span><span class="sig-prename descclassname"><span class="pre">=<time></span></span><a class="headerlink" href="#cmdoption-arg-t_final" title="Permalink to this definition">¶</a></dt> +<dd><p>Final epoch that the coordinate will be propagated to after transformation. +The special epoch <em>now</em> can be used instead of writing a specific period in +time. When <em>now</em> is used, it is replaced internally with the epoch of the +transformation. This means that the resulting coordinate will be slightly +different if carried out again at a later date.</p> +</dd></dl> + +<div class="versionadded"> +<p><span class="versionmodified added">New in version 5.1.0.</span></p> +</div> +</section> +</section> +</section> + + + </div> + </div> + <footer><div class="rst-footer-buttons" role="navigation" aria-label="Footer"> + <a href="molobadekas.html" class="btn btn-neutral float-left" title="Molodensky-Badekas transform" accesskey="p" rel="prev"><span class="fa fa-arrow-circle-left" aria-hidden="true"></span> Previous</a> + <a href="tinshift.html" class="btn btn-neutral float-right" title="Triangulated Irregular Network based transformation" 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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