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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="proj-rfc-6-triangulation-based-transformations"> +<span id="rfc6"></span><h1>PROJ RFC 6: Triangulation-based transformations<a class="headerlink" href="#proj-rfc-6-triangulation-based-transformations" title="Permalink to this headline">¶</a></h1> +<dl class="field-list simple"> +<dt class="field-odd">Author</dt> +<dd class="field-odd"><p>Even Rouault</p> +</dd> +<dt class="field-even">Contact</dt> +<dd class="field-even"><p><a class="reference external" href="mailto:even.rouault%40spatialys.com">even<span>.</span>rouault<span>@</span>spatialys<span>.</span>com</a></p> +</dd> +<dt class="field-odd">Status</dt> +<dd class="field-odd"><p>Adopted</p> +</dd> +<dt class="field-even">Implementation target</dt> +<dd class="field-even"><p>PROJ 7.2</p> +</dd> +<dt class="field-odd">Last Updated</dt> +<dd class="field-odd"><p>2020-09-02</p> +</dd> +</dl> +<section id="summary"> +<h2>Summary<a class="headerlink" href="#summary" title="Permalink to this headline">¶</a></h2> +<p>This RFC adds a new transformation method, <code class="docutils literal notranslate"><span class="pre">tinshift</span></code> (TIN stands for +Triangulated Irregular Network)</p> +<p>The motivation for this work is to be able to handle the official transformations +created by National Land Survey of Finland, for:</p> +<ul class="simple"> +<li><p>horizontal transformation between the KKJ and ETRS89 horizontal datums</p></li> +<li><p>vertical transformations between N43 and N60 heights, and N60 and N2000 heights.</p></li> +</ul> +<p>Such transformations are somehow related to traditional grid-based transformations, +except that the correction values are hold by the vertices of the triangulation, +instead of being at nodes of a grid.</p> +<p>Triangulation are in a number of cases the initial product of a geodesic adjustment, +with grids being a derived product. The Swiss grids have for example +derived products of an original triangulation.</p> +<p>Grid-based transformations remain very convenient to use because accessing +correction values is really easy and efficient, so triangulation-based transformations +are not meant as replacing them, but more about it being a complement, that is +sometimes necessary to be able to replicate the results of a officially vetted +transformation to a millimetric or better precision (speaking here about reproducibility +of numeric results, rather than the physical accuracy of the transformation that +might rather be centimetric). It is always possible to approach the result of +the triangulation with a grid, but that may require to adopt a small grid step, +and thus generate a grid that can be much larger than the original triangulation.</p> +</section> +<section id="details"> +<h2>Details<a class="headerlink" href="#details" title="Permalink to this headline">¶</a></h2> +<section id="transformation"> +<h3>Transformation<a class="headerlink" href="#transformation" title="Permalink to this headline">¶</a></h3> +<p>A new transformation method, <code class="docutils literal notranslate"><span class="pre">tinshift</span></code>, is added. It takes one mandatory +argument, <code class="docutils literal notranslate"><span class="pre">file</span></code>, that points to a JSON file, which contains the triangulation +and associated metadata. Input and output coordinates must be geographic or projected. +Depending on the content +of the JSON file, horizontal, vertical or both components of the coordinates may +be transformed.</p> +<p>The transformation is used like:</p> +<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>$ echo 3210000.0000 6700000.0000 0 2020 | cct +proj=tinshift +file=./triangulation_kkj.json + +209948.3217 6697187.0009 0.0000 2020 +</pre></div> +</div> +<p>The transformation is invertible, with the same computational complexity than +the forward transformation.</p> +</section> +<section id="algorithm"> +<h3>Algorithm<a class="headerlink" href="#algorithm" title="Permalink to this headline">¶</a></h3> +<p>Internally, <code class="docutils literal notranslate"><span class="pre">tinshift</span></code> ingest the whole file into memory. It is considered that +triangulation should be small enough for that. The above mentioned KKJ to ETRS89 +triangulation fits into 65 KB of JSON, for 1449 triangles and 767 vertices.</p> +<p>When a point is transformed, one must find the triangle into which it falls into. +Instead of iterating over all triangles, we build a in-memory quadtree to speed-up +the identification of candidates triangles. On the above mentioned KKJ -> ETRS89 +triangulation, this speeds up the whole transformation by a factor of 10. The +quadtree structure is a very good compromise between the performance gain it brings +and the simplicity of its implementation (we have ported the implementation coming +from GDAL, inherit from the one used for shapefile .spx spatial indices).</p> +<p>To determine if a point falls into a triangle, one computes its 3 +<a class="reference external" href="https://en.wikipedia.org/wiki/Barycentric_coordinate_system#Conversion_between_barycentric_and_Cartesian_coordinates">barycentric coordinates</a> +from its projected coordinates, <span class="math notranslate nohighlight">\(\lambda_i\)</span> for <span class="math notranslate nohighlight">\(i=1,2,3\)</span>. +They are real values (in the [0,1] range for a point inside the triangle), +giving the weight of each of the 3 vertices of the triangles.</p> +<p>Once those weights are known, interpolating the target horizontal +coordinate is a matter of doing the linear combination of those weights with +the target horizontal coordinates at the 3 vertices of the triangle (<span class="math notranslate nohighlight">\(Xt_i\)</span> and <span class="math notranslate nohighlight">\(Yt_i\)</span>):</p> +<div class="math notranslate nohighlight"> +\[ \begin{align}\begin{aligned}X_{target} = Xt_1 * \lambda_1 + Xt_2 * \lambda_2 + Xt_3 * \lambda_3\\Y_{target} = Yt_1 * \lambda_1 + Yt_2 * \lambda_2 + Yt_3 * \lambda_3\end{aligned}\end{align} \]</div> +<p>This interpolation is exact at the vertices of the triangulation, and has linear properties +inside each triangle. It is completely equivalent to other formulations of +triangular interpolation, such as</p> +<div class="math notranslate nohighlight"> +\[ \begin{align}\begin{aligned}X_{target} = A + X_{source} * B + Y_{source} * C\\Y_{target} = D + X_{source} * E + Y_{source} * F\end{aligned}\end{align} \]</div> +<p>where the A, B, C, D, E, F constants (for a given triangle) are found by solving +the 2 systems of 3 linear equations, constraint by the source and target coordinate pairs +of the 3 vertices of the triangle:</p> +<div class="math notranslate nohighlight"> +\[ \begin{align}\begin{aligned}Xt_i = A + Xs_i * B + Ys_i * C\\Yt_i = D + Xs_i * E + Ys_i * F\end{aligned}\end{align} \]</div> +<div class="admonition note"> +<p class="admonition-title">Note</p> +<p>From experiments, the interpolation using barycentric coordinates is slightly +more numerically robust when interpolating projected coordinates of amplitude of the +order of 1e5 / 1e6, due to computations involving differences of coordinates. +Whereas the formulation with the A, B, C, D, E, F tends to have big values for +the A and D constants, and values clause to 0 for C and E, and close to 1 for +B and F. However, the difference between the two approaches is negligible for +practical purposes (below micrometre precision)</p> +</div> +<p>Similarly for a vertical coordinate transformation, where <span class="math notranslate nohighlight">\(Zoff_i\)</span> is the vertical +offset at each vertex of the triangle:</p> +<div class="math notranslate nohighlight"> +\[Z_{target} = Z_{source} + Zoff_1 * \lambda_1 + Zoff_2 * \lambda_2 + Zoff_3 * \lambda_3\]</div> +</section> +<section id="constraints-on-the-triangulation"> +<h3>Constraints on the triangulation<a class="headerlink" href="#constraints-on-the-triangulation" title="Permalink to this headline">¶</a></h3> +<p>No check is done on the consistence of the triangulation. It is highly +recommended that triangles do not overlap each other (when considering the +source coordinates or the forward transformation, or the target coordinates for +the inverse transformation), otherwise which triangle will be selected is +unspecified. Besides that, the triangulation does not need to have particular +properties (like being a Delaunay triangulation)</p> +</section> +<section id="file-format"> +<h3>File format<a class="headerlink" href="#file-format" title="Permalink to this headline">¶</a></h3> +<p>To the best of our knowledge, there are no established file formats to convey +geodetic transformations as triangulations. Potential similar formats to store TINs +are <a class="reference external" href="http://vterrain.org/Implementation/Formats/ITF.html">ITF</a> or +<a class="reference external" href="https://www.xmswiki.com/wiki/TIN_Files">XMS</a>. +Both of them would need to be extended in order to handle datum shift information, +since they are both intended for mostly DEM use.</p> +<p>We thus propose a text-based format, using JSON as a serialization. Using a text-based +format could potentially be thought as a limitation performance-wise compared to +binary formats, but for the size of triangulations considered (a few thousands triangles / vertices), +there is no issue. Loading such file is a matter of 20 milliseconds or so. For reference, +loading a triangulation of about 115 000 triangles and 71 000 vertices takes 450 ms.</p> +<p>Using JSON provides generic formatting and parsing rules, and convenience to +create it from Python script for examples. This could also be easily generated “at hand” +by non-JSON aware writers.</p> +<p>For generic metadata, we reuse closely what has been used for the +<a class="reference external" href="https://github.com/linz/deformation-model-format">Deformation model master file</a></p> +<p>Below a minimal example, from the KKJ to ETRS89 transformation, with just a +single triangle:</p> +<div class="highlight-json notranslate"><div class="highlight"><pre><span></span><span class="p">{</span><span class="w"></span> +<span class="w"> </span><span class="nt">"file_type"</span><span class="p">:</span><span class="w"> </span><span class="s2">"triangulation_file"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"format_version"</span><span class="p">:</span><span class="w"> </span><span class="s2">"1.0"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"name"</span><span class="p">:</span><span class="w"> </span><span class="s2">"Name"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"version"</span><span class="p">:</span><span class="w"> </span><span class="s2">"Version"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"publication_date"</span><span class="p">:</span><span class="w"> </span><span class="s2">"2018-07-01T00:00:00Z"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"license"</span><span class="p">:</span><span class="w"> </span><span class="s2">"Creative Commons Attribution 4.0 International"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"description"</span><span class="p">:</span><span class="w"> </span><span class="s2">"Test triangulation"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"authority"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w"></span> +<span class="w"> </span><span class="nt">"name"</span><span class="p">:</span><span class="w"> </span><span class="s2">"Authority name"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"url"</span><span class="p">:</span><span class="w"> </span><span class="s2">"http://example.com"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"address"</span><span class="p">:</span><span class="w"> </span><span class="s2">"Address"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"email"</span><span class="p">:</span><span class="w"> </span><span class="s2">"test@example.com"</span><span class="w"></span> +<span class="w"> </span><span class="p">},</span><span class="w"></span> +<span class="w"> </span><span class="nt">"links"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="w"></span> +<span class="w"> </span><span class="p">{</span><span class="w"></span> +<span class="w"> </span><span class="nt">"href"</span><span class="p">:</span><span class="w"> </span><span class="s2">"https://example.com/about.html"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"rel"</span><span class="p">:</span><span class="w"> </span><span class="s2">"about"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"type"</span><span class="p">:</span><span class="w"> </span><span class="s2">"text/html"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"title"</span><span class="p">:</span><span class="w"> </span><span class="s2">"About"</span><span class="w"></span> +<span class="w"> </span><span class="p">},</span><span class="w"></span> +<span class="w"> </span><span class="p">{</span><span class="w"></span> +<span class="w"> </span><span class="nt">"href"</span><span class="p">:</span><span class="w"> </span><span class="s2">"https://example.com/download"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"rel"</span><span class="p">:</span><span class="w"> </span><span class="s2">"source"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"type"</span><span class="p">:</span><span class="w"> </span><span class="s2">"application/zip"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"title"</span><span class="p">:</span><span class="w"> </span><span class="s2">"Authoritative source"</span><span class="w"></span> +<span class="w"> </span><span class="p">},</span><span class="w"></span> +<span class="w"> </span><span class="p">{</span><span class="w"></span> +<span class="w"> </span><span class="nt">"href"</span><span class="p">:</span><span class="w"> </span><span class="s2">"https://creativecommons.org/licenses/by/4.0/"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"rel"</span><span class="p">:</span><span class="w"> </span><span class="s2">"license"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"type"</span><span class="p">:</span><span class="w"> </span><span class="s2">"text/html"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"title"</span><span class="p">:</span><span class="w"> </span><span class="s2">"Creative Commons Attribution 4.0 International license"</span><span class="w"></span> +<span class="w"> </span><span class="p">},</span><span class="w"></span> +<span class="w"> </span><span class="p">{</span><span class="w"></span> +<span class="w"> </span><span class="nt">"href"</span><span class="p">:</span><span class="w"> </span><span class="s2">"https://example.com/metadata.xml"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"rel"</span><span class="p">:</span><span class="w"> </span><span class="s2">"metadata"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"type"</span><span class="p">:</span><span class="w"> </span><span class="s2">"application/xml"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"title"</span><span class="p">:</span><span class="w"> </span><span class="s2">" ISO 19115 XML encoded metadata regarding the triangulation"</span><span class="w"></span> +<span class="w"> </span><span class="p">}</span><span class="w"></span> +<span class="w"> </span><span class="p">],</span><span class="w"></span> +<span class="w"> </span><span class="nt">"input_crs"</span><span class="p">:</span><span class="w"> </span><span class="s2">"EPSG:2393"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"target_crs"</span><span class="p">:</span><span class="w"> </span><span class="s2">"EPSG:3067"</span><span class="p">,</span><span class="w"></span> +<span class="w"> </span><span class="nt">"transformed_components"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="w"> </span><span class="s2">"horizontal"</span><span class="w"> </span><span class="p">],</span><span class="w"></span> +<span class="w"> </span><span class="nt">"vertices_columns"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="w"> </span><span class="s2">"source_x"</span><span class="p">,</span><span class="w"> </span><span class="s2">"source_y"</span><span class="p">,</span><span class="w"> </span><span class="s2">"target_x"</span><span class="p">,</span><span class="w"> </span><span class="s2">"target_y"</span><span class="w"> </span><span class="p">],</span><span class="w"></span> +<span class="w"> </span><span class="nt">"triangles_columns"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="w"> </span><span class="s2">"idx_vertex1"</span><span class="p">,</span><span class="w"> </span><span class="s2">"idx_vertex2"</span><span class="p">,</span><span class="w"> </span><span class="s2">"idx_vertex3"</span><span class="w"> </span><span class="p">],</span><span class="w"></span> +<span class="w"> </span><span class="nt">"vertices"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="w"> </span><span class="p">[</span><span class="mf">3244102.707</span><span class="p">,</span><span class="w"> </span><span class="mf">6693710.937</span><span class="p">,</span><span class="w"> </span><span class="mf">244037.137</span><span class="p">,</span><span class="w"> </span><span class="mf">6690900.686</span><span class="p">],</span><span class="w"></span> +<span class="w"> </span><span class="p">[</span><span class="mf">3205290.722</span><span class="p">,</span><span class="w"> </span><span class="mf">6715311.822</span><span class="p">,</span><span class="w"> </span><span class="mf">205240.895</span><span class="p">,</span><span class="w"> </span><span class="mf">6712492.577</span><span class="p">],</span><span class="w"></span> +<span class="w"> </span><span class="p">[</span><span class="mf">3218328.492</span><span class="p">,</span><span class="w"> </span><span class="mf">6649538.429</span><span class="p">,</span><span class="w"> </span><span class="mf">218273.648</span><span class="p">,</span><span class="w"> </span><span class="mf">6646745.973</span><span class="p">]</span><span class="w"> </span><span class="p">],</span><span class="w"></span> +<span class="w"> </span><span class="nt">"triangles"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="w"> </span><span class="p">[</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">]</span><span class="w"> </span><span class="p">]</span><span class="w"></span> +<span class="p">}</span><span class="w"></span> +</pre></div> +</div> +<p>So after the generic metadata, we define the input and output CRS (informative +only), and that the transformation affects horizontal components of +coordinates. We name the columns of the <code class="docutils literal notranslate"><span class="pre">vertices</span></code> and <code class="docutils literal notranslate"><span class="pre">triangles</span></code> arrays. +We defined the source and target coordinates of each vertex, and define a +triangle by referring to the index of its vertices in the <code class="docutils literal notranslate"><span class="pre">vertices</span></code> array.</p> +<p>More formally, the specific items for the triangulation file are:</p> +<dl class="simple"> +<dt>input_crs</dt><dd><p>String identifying the CRS of source coordinates +in the vertices. Typically <code class="docutils literal notranslate"><span class="pre">EPSG:XXXX</span></code>. If the transformation is for vertical +component, this should be the code for a compound CRS (can be EPSG:XXXX+YYYY +where XXXX is the code of the horizontal CRS and YYYY the code of the vertical CRS). +For example, for the KKJ->ETRS89 transformation, this is EPSG:2393 +(<code class="docutils literal notranslate"><span class="pre">KKJ</span> <span class="pre">/</span> <span class="pre">Finland</span> <span class="pre">Uniform</span> <span class="pre">Coordinate</span> <span class="pre">System</span></code>). The input coordinates are assumed +to be passed in the “normalized for visualisation” / “GIS friendly” order, +that is longitude, latitude for geographic coordinates and +easting, northing for projected coordinates.</p> +</dd> +<dt>output_crs</dt><dd><p>String identifying the CRS of target coordinates in the vertices. +Typically <code class="docutils literal notranslate"><span class="pre">EPSG:XXXX</span></code>. If the transformation is for vertical component, +this should be the code for a compound CRS (can be EPSG:XXXX+YYYY where +XXXX is the code of the horizontal CRS and YYYY the code of the vertical CRS). +For example, for the KKJ->ETRS89 transformation, this is EPSG:3067 +("ETRS89 / TM35FIN(E,N)"). The output coordinates will be returned in +the “normalized for visualisation” / “GIS friendly” order, +that is longitude, latitude for geographic coordinates and +easting, northing for projected coordinates.</p> +</dd> +<dt>transformed_components</dt><dd><p>Array which may contain one or two strings: “horizontal” when horizontal +components of the coordinates are transformed and/or “vertical” when the +vertical component is transformed.</p> +</dd> +<dt>vertices_columns</dt><dd><p>Specify the name of the columns of the rows in the <code class="docutils literal notranslate"><span class="pre">vertices</span></code> +array. There must be exactly as many elements in <code class="docutils literal notranslate"><span class="pre">vertices_columns</span></code> as in a +row of <code class="docutils literal notranslate"><span class="pre">vertices</span></code>. The following names have a special meaning: <code class="docutils literal notranslate"><span class="pre">source_x</span></code>, +<code class="docutils literal notranslate"><span class="pre">source_y</span></code>, <code class="docutils literal notranslate"><span class="pre">target_x</span></code>, <code class="docutils literal notranslate"><span class="pre">target_y</span></code>, <code class="docutils literal notranslate"><span class="pre">source_z</span></code>, <code class="docutils literal notranslate"><span class="pre">target_z</span></code> and +<code class="docutils literal notranslate"><span class="pre">offset_z</span></code>. <code class="docutils literal notranslate"><span class="pre">source_x</span></code> and <code class="docutils literal notranslate"><span class="pre">source_y</span></code> are compulsory. +<code class="docutils literal notranslate"><span class="pre">source_x</span></code> is for the source longitude (in degree) or easting. +<code class="docutils literal notranslate"><span class="pre">source_y</span></code> is for the source latitude (in degree) or northing. +<code class="docutils literal notranslate"><span class="pre">target_x</span></code> and <code class="docutils literal notranslate"><span class="pre">target_y</span></code> are compulsory when <code class="docutils literal notranslate"><span class="pre">horizontal</span></code> is specified +in <code class="docutils literal notranslate"><span class="pre">transformed_components</span></code>. (<code class="docutils literal notranslate"><span class="pre">source_z</span></code> and <code class="docutils literal notranslate"><span class="pre">target_z</span></code>) or +<code class="docutils literal notranslate"><span class="pre">offset_z</span></code> are compulsory when <code class="docutils literal notranslate"><span class="pre">vertical</span></code> is specified in <code class="docutils literal notranslate"><span class="pre">transformed_components</span></code></p> +</dd> +<dt>triangles_columns</dt><dd><p>Specify the name of the columns of the rows in the +<code class="docutils literal notranslate"><span class="pre">triangles</span></code> array. There must be exactly as many elements in <code class="docutils literal notranslate"><span class="pre">triangles_columns</span></code> +as in a row of <code class="docutils literal notranslate"><span class="pre">triangles</span></code>. The following names have a special meaning: +<code class="docutils literal notranslate"><span class="pre">idx_vertex1</span></code>, <code class="docutils literal notranslate"><span class="pre">idx_vertex2</span></code>, <code class="docutils literal notranslate"><span class="pre">idx_vertex3</span></code>. They are compulsory.</p> +</dd> +<dt>vertices</dt><dd><p>An array whose items are themselves arrays with as many columns as +described in <code class="docutils literal notranslate"><span class="pre">vertices_columns</span></code>.</p> +</dd> +<dt>triangles</dt><dd><p>An array whose items are themselves arrays with as many columns as +described in <code class="docutils literal notranslate"><span class="pre">triangles_columns</span></code>. +The value of the <code class="docutils literal notranslate"><span class="pre">idx_vertexN</span></code> columns must be indices +(between 0 and len(<code class="docutils literal notranslate"><span class="pre">vertices</span></code>-1) of items of the <code class="docutils literal notranslate"><span class="pre">vertices</span></code> array.</p> +</dd> +</dl> +</section> +<section id="code-impacts"> +<h3>Code impacts<a class="headerlink" href="#code-impacts" title="Permalink to this headline">¶</a></h3> +<p>The following new files are added in src/transformations:</p> +<ul class="simple"> +<li><p>tinshift.cpp: PROJ specific code for defining the new operation. Takes care +of the input and output coordinate conversions (between input_crs and triangulation_source_crs, +and triangulation_target_crs and output_crs), when needed.</p></li> +<li><p>tinshift.hpp: Header-based implementation. This file contains the API.</p></li> +<li><p>tinshift_exceptions.hpp: Exceptions that can be raised during file parsing</p></li> +<li><p>tinshift_impl.hpp: Implementation of file loading, triangle search and interpolation.</p></li> +</ul> +<p>This is the approach that has been followed for the deformation model implementation, +and which makes it easier to do unit test.</p> +<p>src/quadtree.hpp contains a quadtree implementation.</p> +</section> +<section id="performance-indications"> +<h3>Performance indications<a class="headerlink" href="#performance-indications" title="Permalink to this headline">¶</a></h3> +<p>Tested on Intel(R) Core(TM) i7-6700HQ CPU @ 2.60GHz, transforming 4 million points</p> +<p>For the KKJ to ETRS89 transformation (1449 triangles and 767 vertices), +4.4 million points / sec can be transformed.</p> +<p>For comparison, the Helmert-based KKJ to ETRS89 transformation operates at +1.6 million points / sec.</p> +<p>A triangulation with about 115 000 triangles and 71 000 vertices +operates at 2.2 million points / sec +(throughput on more points would be better since the initial loading of the +triangulation is non-negligible here)</p> +</section> +</section> +<section id="backward-compatibility"> +<h2>Backward compatibility<a class="headerlink" href="#backward-compatibility" title="Permalink to this headline">¶</a></h2> +<p>New functionality fully backward compatible.</p> +</section> +<section id="testing"> +<h2>Testing<a class="headerlink" href="#testing" title="Permalink to this headline">¶</a></h2> +<p>The PROJ test suite will be enhanced to test the new transformation, with a +new .gie file, and a C++ unit test to test at a lower level.</p> +</section> +<section id="documentation"> +<h2>Documentation<a class="headerlink" href="#documentation" title="Permalink to this headline">¶</a></h2> +<ul class="simple"> +<li><p>The tinshift method will be documented.</p></li> +<li><p>The JSON format will be documented under <a class="reference external" href="https://proj.org/specifications/">https://proj.org/specifications/</a></p></li> +<li><p>A JSON schema will also be provided.</p></li> +</ul> +</section> +<section id="proposed-implementation"> +<h2>Proposed implementation<a class="headerlink" href="#proposed-implementation" title="Permalink to this headline">¶</a></h2> +<p>An initial implementation is available at <a class="reference external" href="https://github.com/rouault/PROJ/tree/tinshift">https://github.com/rouault/PROJ/tree/tinshift</a></p> +</section> +<section id="references"> +<h2>References<a class="headerlink" href="#references" title="Permalink to this headline">¶</a></h2> +<p><a class="reference external" href="https://translate.google.fr/translate?sl=auto&tl=en&u=https%3A%2F%2Fwww.maanmittauslaitos.fi%2Fkartat-ja-paikkatieto%2Fasiantuntevalle-kayttajalle%2Fkoordinaattimuunnokset">Finnish coordinate transformation (automated translation to English)</a></p> +</section> +<section id="adoption-status"> +<h2>Adoption status<a class="headerlink" href="#adoption-status" title="Permalink to this headline">¶</a></h2> +<p>The RFC was adopted on 2020-09-02 with +1’s from the following PSC members</p> +<ul class="simple"> +<li><p>Kristian Evers</p></li> +<li><p>Charles Karney</p></li> +<li><p>Thomas Knudsen</p></li> +<li><p>Even Rouault</p></li> +</ul> +</section> +<section id="funding"> +<h2>Funding<a class="headerlink" href="#funding" title="Permalink to this headline">¶</a></h2> +<p>This work is funded by <a class="reference external" href="https://www.maanmittauslaitos.fi/en">National Land Survey of Finland</a></p> +</section> +</section> + + + </div> + </div> + <footer><div class="rst-footer-buttons" role="navigation" aria-label="Footer"> + <a href="rfc-5.html" class="btn btn-neutral float-left" title="PROJ RFC 5: Adopt GeoTIFF-based grids for grids delivered with PROJ" accesskey="p" rel="prev"><span class="fa fa-arrow-circle-left" aria-hidden="true"></span> Previous</a> + <a href="rfc-7.html" class="btn btn-neutral float-right" title="PROJ RFC 7: Drop Autotools, maintain CMake" 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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