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<section id="quick-start">
<span id="dev-quickstart"></span><h1>Quick start<a class="headerlink" href="#quick-start" title="Permalink to this headline">¶</a></h1>
<p>This is a short introduction to the PROJ API. In the following section we
create a simple program that transforms a geodetic coordinate to UTM and back
again. The program is explained a few lines at a time. The complete program can
be seen at the end of the section.</p>
<p>See the following sections for more in-depth descriptions of different parts of
the PROJ API or consult the <a class="reference internal" href="reference/index.html"><span class="doc">API reference</span></a> for specifics.</p>
<p>Before the PROJ API can be used it is necessary to include the <code class="file docutils literal notranslate"><span class="pre">proj.h</span></code> header
file. Here <code class="file docutils literal notranslate"><span class="pre">stdio.h</span></code> is also included so we can print some text to the screen:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><stdio.h></span><span class="cp"></span>
<span class="cp">#include</span><span class="w"> </span><span class="cpf"><proj.h></span><span class="cp"></span>
</pre></div>
</div>
<p>Let’s declare a few variables that’ll be used later in the program. Each variable
will be discussed below.
See the <a class="reference internal" href="reference/datatypes.html"><span class="doc">reference for more info on data types</span></a>.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">PJ_CONTEXT</span><span class="w"> </span><span class="o">*</span><span class="n">C</span><span class="p">;</span><span class="w"></span>
<span class="n">PJ</span><span class="w"> </span><span class="o">*</span><span class="n">P</span><span class="p">;</span><span class="w"></span>
<span class="n">PJ</span><span class="w"> </span><span class="o">*</span><span class="n">norm</span><span class="p">;</span><span class="w"></span>
<span class="n">PJ_COORD</span><span class="w"> </span><span class="n">a</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">;</span><span class="w"></span>
</pre></div>
</div>
<p>For use in multi-threaded programs the <a class="reference internal" href="reference/datatypes.html#c.PJ_CONTEXT" title="PJ_CONTEXT"><code class="xref c c-type docutils literal notranslate"><span class="pre">PJ_CONTEXT</span></code></a> threading-context
is used. In this particular example it is not needed, but for the sake of
completeness we demonstrate its use here.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">C</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">proj_context_create</span><span class="p">();</span><span class="w"></span>
</pre></div>
</div>
<p>Next we create the <a class="reference internal" href="reference/datatypes.html#c.PJ" title="PJ"><code class="xref c c-type docutils literal notranslate"><span class="pre">PJ</span></code></a> transformation object <code class="docutils literal notranslate"><span class="pre">P</span></code> with the function
<a class="reference internal" href="reference/functions.html#c.proj_create_crs_to_crs" title="proj_create_crs_to_crs"><code class="xref c c-func docutils literal notranslate"><span class="pre">proj_create_crs_to_crs()</span></code></a>.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">proj_create_crs_to_crs</span><span class="w"> </span><span class="p">(</span><span class="n">C</span><span class="p">,</span><span class="w"></span>
<span class="w"> </span><span class="s">"EPSG:4326"</span><span class="p">,</span><span class="w"></span>
<span class="w"> </span><span class="s">"+proj=utm +zone=32 +datum=WGS84"</span><span class="p">,</span><span class="w"> </span><span class="cm">/* or EPSG:32632 */</span><span class="w"></span>
<span class="w"> </span><span class="nb">NULL</span><span class="p">);</span><span class="w"></span>
<span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="mi">0</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">P</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span><span class="w"> </span><span class="s">"Failed to create transformation object.</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
</pre></div>
</div>
<p>Here we have set up a transformation from geographic coordinates to UTM zone
32N.</p>
<p><a class="reference internal" href="reference/functions.html#c.proj_create_crs_to_crs" title="proj_create_crs_to_crs"><code class="xref c c-func docutils literal notranslate"><span class="pre">proj_create_crs_to_crs()</span></code></a> takes as its arguments:</p>
<ul class="simple">
<li><p>the threading context <code class="docutils literal notranslate"><span class="pre">C</span></code> created above,</p></li>
<li><p>a string that describes the source coordinate reference system (CRS),</p></li>
<li><p>a string that describes the target CRS and</p></li>
<li><p>an optional description of the area of use.</p></li>
</ul>
<p>It is recommended to create one threading context per thread used by the
program. This ensures that all <a class="reference internal" href="reference/datatypes.html#c.PJ" title="PJ"><code class="xref c c-type docutils literal notranslate"><span class="pre">PJ</span></code></a> objects created in the same
context will be sharing resources such as error-numbers and loaded grids.</p>
<p>If you are sure that <code class="docutils literal notranslate"><span class="pre">P</span></code> will only be used by a single program thread, you
may pass <code class="docutils literal notranslate"><span class="pre">NULL</span></code> for the threading context. This will assign the default
thread context to <code class="docutils literal notranslate"><span class="pre">P</span></code>.</p>
<p>The strings for the source and target CRS may be any of:</p>
<ul class="simple">
<li><p>PROJ strings, e.g. <code class="docutils literal notranslate"><span class="pre">+proj=longlat</span> <span class="pre">+datum=WGS84</span> <span class="pre">+type=crs</span></code>,</p></li>
<li><p>CRS identified by their code, e.g. <code class="docutils literal notranslate"><span class="pre">EPSG:4326</span></code> or
<code class="docutils literal notranslate"><span class="pre">urn:ogc:def:crs:EPSG::4326</span></code>, or</p></li>
<li><p>a well-known text (WKT) string, e.g.:</p></li>
</ul>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>GEOGCRS["WGS 84",
DATUM["World Geodetic System 1984",
ELLIPSOID["WGS 84",6378137,298.257223563,
LENGTHUNIT["metre",1]]],
PRIMEM["Greenwich",0,
ANGLEUNIT["degree",0.0174532925199433]],
CS[ellipsoidal,2],
AXIS["geodetic latitude (Lat)",north,
ORDER[1],
ANGLEUNIT["degree",0.0174532925199433]],
AXIS["geodetic longitude (Lon)",east,
ORDER[2],
ANGLEUNIT["degree",0.0174532925199433]],
USAGE[
SCOPE["unknown"],
AREA["World"],
BBOX[-90,-180,90,180]],
ID["EPSG",4326]]
</pre></div>
</div>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>The use of PROJ strings to describe a CRS is not recommended. One of the
main weaknesses of PROJ strings is their inability to describe a geodetic
datum, other than the few ones hardcoded in the <code class="docutils literal notranslate"><span class="pre">+datum</span></code> parameter.</p>
</div>
<p><a class="reference internal" href="reference/functions.html#c.proj_create_crs_to_crs" title="proj_create_crs_to_crs"><code class="xref c c-func docutils literal notranslate"><span class="pre">proj_create_crs_to_crs()</span></code></a> will return a pointer to a <a class="reference internal" href="reference/datatypes.html#c.PJ" title="PJ"><code class="xref c c-type docutils literal notranslate"><span class="pre">PJ</span></code></a>
object, or a null pointer in the case of an error. The details of the error
can be retrieved using <a class="reference internal" href="reference/functions.html#c.proj_context_errno" title="proj_context_errno"><code class="xref c c-func docutils literal notranslate"><span class="pre">proj_context_errno()</span></code></a>. See <a class="reference internal" href="errorhandling.html"><span class="doc">Error handling</span></a>
for further details.</p>
<p>Now that we have a normalized transformation object in <code class="docutils literal notranslate"><span class="pre">P</span></code>, we can use it
with <a class="reference internal" href="reference/functions.html#c.proj_trans" title="proj_trans"><code class="xref c c-func docutils literal notranslate"><span class="pre">proj_trans()</span></code></a> to transform coordinates from the source CRS to the
target CRS, but first we will discuss the interpretation of coordinates.</p>
<p>By default, a <a class="reference internal" href="reference/datatypes.html#c.PJ" title="PJ"><code class="xref c c-type docutils literal notranslate"><span class="pre">PJ</span></code></a> transformation object accepts coordinates expressed
in the units and axis order of the source CRS, and returns transformed
coordinates in the units and axis order of the target CRS.</p>
<p>For most geographic CRS, the units will be in degrees. In rare cases, such as
EPSG:4807 / NTF (Paris), this can be grads. For geographic CRS defined by the
EPSG authority, the order of coordinates is latitude first, longitude second.
When using a PROJ string, the order is the reverse; longitude first, latitude
second.</p>
<p>For projected CRS, the units may vary (metre, us-foot, etc.). For projected CRS
defined by the EPSG authority, and with EAST / NORTH directions, the order
might be easting first, northing second, or the reverse. When using a PROJ
string, the order will be easting first, northing second, except if the
<code class="docutils literal notranslate"><span class="pre">+axis</span></code> parameter modifies it.</p>
<p>If you prefer to work with a uniform axis order, regardless of the axis orders
mandated by the source and target CRS, you can use the
<a class="reference internal" href="reference/functions.html#c.proj_normalize_for_visualization" title="proj_normalize_for_visualization"><code class="xref c c-func docutils literal notranslate"><span class="pre">proj_normalize_for_visualization()</span></code></a> function.</p>
<p><a class="reference internal" href="reference/functions.html#c.proj_normalize_for_visualization" title="proj_normalize_for_visualization"><code class="xref c c-func docutils literal notranslate"><span class="pre">proj_normalize_for_visualization()</span></code></a> takes a threading context and an
existing <a class="reference internal" href="reference/datatypes.html#c.PJ" title="PJ"><code class="xref c c-type docutils literal notranslate"><span class="pre">PJ</span></code></a> object, and generates from it a new <a class="reference internal" href="reference/datatypes.html#c.PJ" title="PJ"><code class="xref c c-type docutils literal notranslate"><span class="pre">PJ</span></code></a> that
accepts as input and returns as output coordinates using the traditional GIS
order. That is, longitude followed by latitude, optionally followed by
elevation and time for geographic CRS, and easting followed by northing for
most projected CRS.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">norm</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">proj_normalize_for_visualization</span><span class="p">(</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">P</span><span class="p">);</span><span class="w"></span>
<span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="mi">0</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">norm</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w"> </span><span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span><span class="w"> </span><span class="s">"Failed to normalize transformation object.</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span><span class="w"></span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
<span class="n">proj_destroy</span><span class="p">(</span><span class="n">P</span><span class="p">);</span><span class="w"></span>
<span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">norm</span><span class="p">;</span><span class="w"></span>
</pre></div>
</div>
<p>Next we create a <a class="reference internal" href="reference/datatypes.html#c.PJ_COORD" title="PJ_COORD"><code class="xref c c-type docutils literal notranslate"><span class="pre">PJ_COORD</span></code></a> coordinate object, using the function
<a class="reference internal" href="reference/functions.html#c.proj_coord" title="proj_coord"><code class="xref c c-func docutils literal notranslate"><span class="pre">proj_coord()</span></code></a>.</p>
<p>The following example creates a coordinate for 55°N 12°E (Copenhagen).</p>
<p>Because we have normalized the transformation object with
<a class="reference internal" href="reference/functions.html#c.proj_normalize_for_visualization" title="proj_normalize_for_visualization"><code class="xref c c-func docutils literal notranslate"><span class="pre">proj_normalize_for_visualization()</span></code></a>, the order of coordinates is
longitude followed by latitude, and the units are degrees.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">a</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">proj_coord</span><span class="p">(</span><span class="mi">12</span><span class="p">,</span><span class="w"> </span><span class="mi">55</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">);</span><span class="w"></span>
</pre></div>
</div>
<p>Now we are ready to transform the coordinate into UTM zone 32, using the
function <a class="reference internal" href="reference/functions.html#c.proj_trans" title="proj_trans"><code class="xref c c-func docutils literal notranslate"><span class="pre">proj_trans()</span></code></a>.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">b</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">proj_trans</span><span class="p">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="n">PJ_FWD</span><span class="p">,</span><span class="w"> </span><span class="n">a</span><span class="p">);</span><span class="w"></span>
<span class="n">printf</span><span class="p">(</span><span class="s">"easting: %.3f, northing: %.3f</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">.</span><span class="n">enu</span><span class="p">.</span><span class="n">e</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">.</span><span class="n">enu</span><span class="p">.</span><span class="n">n</span><span class="p">);</span><span class="w"></span>
</pre></div>
</div>
<p><a class="reference internal" href="reference/functions.html#c.proj_trans" title="proj_trans"><code class="xref c c-func docutils literal notranslate"><span class="pre">proj_trans()</span></code></a> takes as its arguments:</p>
<ul class="simple">
<li><p>a <a class="reference internal" href="reference/datatypes.html#c.PJ" title="PJ"><code class="xref c c-type docutils literal notranslate"><span class="pre">PJ</span></code></a> transformation object,</p></li>
<li><p>a <a class="reference internal" href="reference/datatypes.html#c.PJ_DIRECTION" title="PJ_DIRECTION"><code class="xref c c-type docutils literal notranslate"><span class="pre">PJ_DIRECTION</span></code></a> direction, and</p></li>
<li><p>the <a class="reference internal" href="reference/datatypes.html#c.PJ_COORD" title="PJ_COORD"><code class="xref c c-type docutils literal notranslate"><span class="pre">PJ_COORD</span></code></a> coordinate to transform.</p></li>
</ul>
<p>The direction argument can be one of:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">PJ_FWD</span></code> – “forward” transformation from source CRS to target CRS.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">PJ_IDENT</span></code> – “identity”, return the source coordinate unchanged.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">PJ_INV</span></code> – “inverse” transformation from target CRS to source CRS.</p></li>
</ul>
<p>It returns the new transformed <a class="reference internal" href="reference/datatypes.html#c.PJ_COORD" title="PJ_COORD"><code class="xref c c-type docutils literal notranslate"><span class="pre">PJ_COORD</span></code></a> coordinate.</p>
<p>We can perform the transformation in reverse (from UTM zone 32 back to
geographic) as follows:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">b</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">proj_trans</span><span class="p">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="n">PJ_INV</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">);</span><span class="w"></span>
<span class="n">printf</span><span class="p">(</span><span class="s">"longitude: %g, latitude: %g</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">.</span><span class="n">lp</span><span class="p">.</span><span class="n">lam</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">.</span><span class="n">lp</span><span class="p">.</span><span class="n">phi</span><span class="p">);</span><span class="w"></span>
</pre></div>
</div>
<p>Before ending the program, we need to release the memory allocated to our
objects:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">proj_destroy</span><span class="p">(</span><span class="n">P</span><span class="p">);</span><span class="w"></span>
<span class="n">proj_context_destroy</span><span class="p">(</span><span class="n">C</span><span class="p">);</span><span class="w"> </span><span class="cm">/* may be omitted in the single threaded case */</span><span class="w"></span>
</pre></div>
</div>
<p>A complete compilable version of the example code can be seen below:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="linenos"> 1</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><stdio.h></span><span class="cp"></span>
<span class="linenos"> 2</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><proj.h></span><span class="cp"></span>
<span class="linenos"> 3</span>
<span class="linenos"> 4</span><span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="w"> </span><span class="p">(</span><span class="kt">void</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="linenos"> 5</span><span class="w"> </span><span class="n">PJ_CONTEXT</span><span class="w"> </span><span class="o">*</span><span class="n">C</span><span class="p">;</span><span class="w"></span>
<span class="linenos"> 6</span><span class="w"> </span><span class="n">PJ</span><span class="w"> </span><span class="o">*</span><span class="n">P</span><span class="p">;</span><span class="w"></span>
<span class="linenos"> 7</span><span class="w"> </span><span class="n">PJ</span><span class="w"> </span><span class="o">*</span><span class="n">norm</span><span class="p">;</span><span class="w"></span>
<span class="linenos"> 8</span><span class="w"> </span><span class="n">PJ_COORD</span><span class="w"> </span><span class="n">a</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">;</span><span class="w"></span>
<span class="linenos"> 9</span>
<span class="linenos">10</span><span class="w"> </span><span class="cm">/* or you may set C=PJ_DEFAULT_CTX if you are sure you will */</span><span class="w"></span>
<span class="linenos">11</span><span class="w"> </span><span class="cm">/* use PJ objects from only one thread */</span><span class="w"></span>
<span class="linenos">12</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">proj_context_create</span><span class="p">();</span><span class="w"></span>
<span class="linenos">13</span>
<span class="linenos">14</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">proj_create_crs_to_crs</span><span class="w"> </span><span class="p">(</span><span class="n">C</span><span class="p">,</span><span class="w"></span>
<span class="linenos">15</span><span class="w"> </span><span class="s">"EPSG:4326"</span><span class="p">,</span><span class="w"></span>
<span class="linenos">16</span><span class="w"> </span><span class="s">"+proj=utm +zone=32 +datum=WGS84"</span><span class="p">,</span><span class="w"> </span><span class="cm">/* or EPSG:32632 */</span><span class="w"></span>
<span class="linenos">17</span><span class="w"> </span><span class="nb">NULL</span><span class="p">);</span><span class="w"></span>
<span class="linenos">18</span>
<span class="linenos">19</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="mi">0</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">P</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="linenos">20</span><span class="w"> </span><span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span><span class="w"> </span><span class="s">"Failed to create transformation object.</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span><span class="w"></span>
<span class="linenos">21</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w"></span>
<span class="linenos">22</span><span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="linenos">23</span>
<span class="linenos">24</span><span class="w"> </span><span class="cm">/* This will ensure that the order of coordinates for the input CRS */</span><span class="w"></span>
<span class="linenos">25</span><span class="w"> </span><span class="cm">/* will be longitude, latitude, whereas EPSG:4326 mandates latitude, */</span><span class="w"></span>
<span class="linenos">26</span><span class="w"> </span><span class="cm">/* longitude */</span><span class="w"></span>
<span class="linenos">27</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">proj_normalize_for_visualization</span><span class="p">(</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">P</span><span class="p">);</span><span class="w"></span>
<span class="linenos">28</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="mi">0</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">norm</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="linenos">29</span><span class="w"> </span><span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span><span class="w"> </span><span class="s">"Failed to normalize transformation object.</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span><span class="w"></span>
<span class="linenos">30</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w"></span>
<span class="linenos">31</span><span class="w"> </span><span class="p">}</span><span class="w"></span>
<span class="linenos">32</span><span class="w"> </span><span class="n">proj_destroy</span><span class="p">(</span><span class="n">P</span><span class="p">);</span><span class="w"></span>
<span class="linenos">33</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">norm</span><span class="p">;</span><span class="w"></span>
<span class="linenos">34</span>
<span class="linenos">35</span><span class="w"> </span><span class="cm">/* a coordinate union representing Copenhagen: 55d N, 12d E */</span><span class="w"></span>
<span class="linenos">36</span><span class="w"> </span><span class="cm">/* Given that we have used proj_normalize_for_visualization(), the order of</span>
<span class="linenos">37</span><span class="cm"> /* coordinates is longitude, latitude, and values are expressed in degrees. */</span><span class="w"></span>
<span class="linenos">38</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">proj_coord</span><span class="p">(</span><span class="mi">12</span><span class="p">,</span><span class="w"> </span><span class="mi">55</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">);</span><span class="w"></span>
<span class="linenos">39</span>
<span class="linenos">40</span><span class="w"> </span><span class="cm">/* transform to UTM zone 32, then back to geographical */</span><span class="w"></span>
<span class="linenos">41</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">proj_trans</span><span class="p">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="n">PJ_FWD</span><span class="p">,</span><span class="w"> </span><span class="n">a</span><span class="p">);</span><span class="w"></span>
<span class="linenos">42</span><span class="w"> </span><span class="n">printf</span><span class="p">(</span><span class="s">"easting: %.3f, northing: %.3f</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">.</span><span class="n">enu</span><span class="p">.</span><span class="n">e</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">.</span><span class="n">enu</span><span class="p">.</span><span class="n">n</span><span class="p">);</span><span class="w"></span>
<span class="linenos">43</span>
<span class="linenos">44</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">proj_trans</span><span class="p">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="n">PJ_INV</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">);</span><span class="w"></span>
<span class="linenos">45</span><span class="w"> </span><span class="n">printf</span><span class="p">(</span><span class="s">"longitude: %g, latitude: %g</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">.</span><span class="n">lp</span><span class="p">.</span><span class="n">lam</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">.</span><span class="n">lp</span><span class="p">.</span><span class="n">phi</span><span class="p">);</span><span class="w"></span>
<span class="linenos">46</span>
<span class="linenos">47</span><span class="w"> </span><span class="cm">/* Clean up */</span><span class="w"></span>
<span class="linenos">48</span><span class="w"> </span><span class="n">proj_destroy</span><span class="p">(</span><span class="n">P</span><span class="p">);</span><span class="w"></span>
<span class="linenos">49</span><span class="w"> </span><span class="n">proj_context_destroy</span><span class="p">(</span><span class="n">C</span><span class="p">);</span><span class="w"> </span><span class="cm">/* may be omitted in the single threaded case */</span><span class="w"></span>
<span class="linenos">50</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"></span>
<span class="linenos">51</span><span class="p">}</span><span class="w"></span>
</pre></div>
</div>
</section>
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