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<div class="titlepage"><div><div><h4 class="title">
<a name="geometry.reference.algorithms.union_"></a><a class="link" href="union_.html" title="union_">union_</a>
</h4></div></div></div>
<p>
<a class="indexterm" name="idp118852224"></a>
Combines two geometries which each other.
</p>
<h6>
<a name="geometry.reference.algorithms.union_.h0"></a>
<span class="phrase"><a name="geometry.reference.algorithms.union_.description"></a></span><a class="link" href="union_.html#geometry.reference.algorithms.union_.description">Description</a>
</h6>
<p>
The free function union calculates the spatial set theoretic union of two
geometries.
</p>
<h6>
<a name="geometry.reference.algorithms.union_.h1"></a>
<span class="phrase"><a name="geometry.reference.algorithms.union_.synopsis"></a></span><a class="link" href="union_.html#geometry.reference.algorithms.union_.synopsis">Synopsis</a>
</h6>
<p>
</p>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Geometry1</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Geometry2</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Collection</span><span class="special">&gt;</span>
<span class="keyword">void</span> <span class="identifier">union_</span><span class="special">(</span><span class="identifier">Geometry1</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="identifier">geometry1</span><span class="special">,</span> <span class="identifier">Geometry2</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="identifier">geometry2</span><span class="special">,</span> <span class="identifier">Collection</span> <span class="special">&amp;</span> <span class="identifier">output_collection</span><span class="special">)</span></pre>
<p>
</p>
<h6>
<a name="geometry.reference.algorithms.union_.h2"></a>
<span class="phrase"><a name="geometry.reference.algorithms.union_.parameters"></a></span><a class="link" href="union_.html#geometry.reference.algorithms.union_.parameters">Parameters</a>
</h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Type
</p>
</th>
<th>
<p>
Concept
</p>
</th>
<th>
<p>
Name
</p>
</th>
<th>
<p>
Description
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
Geometry1 const &amp;
</p>
</td>
<td>
<p>
Any type fulfilling a Geometry Concept
</p>
</td>
<td>
<p>
geometry1
</p>
</td>
<td>
<p>
A model of the specified concept
</p>
</td>
</tr>
<tr>
<td>
<p>
Geometry2 const &amp;
</p>
</td>
<td>
<p>
Any type fulfilling a Geometry Concept
</p>
</td>
<td>
<p>
geometry2
</p>
</td>
<td>
<p>
A model of the specified concept
</p>
</td>
</tr>
<tr>
<td>
<p>
Collection &amp;
</p>
</td>
<td>
<p>
output collection, either a multi-geometry, or a std::vector&lt;Geometry&gt;
/ std::deque&lt;Geometry&gt; etc
</p>
</td>
<td>
<p>
output_collection
</p>
</td>
<td>
<p>
the output collection
</p>
</td>
</tr>
</tbody>
</table></div>
<h6>
<a name="geometry.reference.algorithms.union_.h3"></a>
<span class="phrase"><a name="geometry.reference.algorithms.union_.header"></a></span><a class="link" href="union_.html#geometry.reference.algorithms.union_.header">Header</a>
</h6>
<p>
Either
</p>
<p>
<code class="computeroutput"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
</p>
<p>
Or
</p>
<p>
<code class="computeroutput"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">/</span><span class="identifier">algorithms</span><span class="special">/</span><span class="keyword">union</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
</p>
<h6>
<a name="geometry.reference.algorithms.union_.h4"></a>
<span class="phrase"><a name="geometry.reference.algorithms.union_.conformance"></a></span><a class="link" href="union_.html#geometry.reference.algorithms.union_.conformance">Conformance</a>
</h6>
<p>
The function union implements function Union from the <a href="http://www.opengeospatial.org/standards/sfa" target="_top">OGC
Simple Feature Specification</a>.
</p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
Boost.Geometry adds an underscore to avoid using the <code class="computeroutput"><span class="keyword">union</span></code>
keyword
</p></td></tr>
</table></div>
<h6>
<a name="geometry.reference.algorithms.union_.h5"></a>
<span class="phrase"><a name="geometry.reference.algorithms.union_.behavior"></a></span><a class="link" href="union_.html#geometry.reference.algorithms.union_.behavior">Behavior</a>
</h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Case
</p>
</th>
<th>
<p>
Behavior
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
GeometryOut is a Point
</p>
</td>
<td>
<p>
Calculates union linestrings of input (multi)points
</p>
</td>
</tr>
<tr>
<td>
<p>
GeometryOut is a Linestring
</p>
</td>
<td>
<p>
Calculates union linestrings of input (multi)linestrings
</p>
</td>
</tr>
<tr>
<td>
<p>
GeometryOut is a Polygon
</p>
</td>
<td>
<p>
Calculates union polygons of input (multi)polygons and/or boxes
</p>
</td>
</tr>
</tbody>
</table></div>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
Check the <a class="link" href="../concepts/concept_polygon.html" title="Polygon Concept">Polygon
Concept</a> for the rules that polygon input for this algorithm should
fulfill
</p></td></tr>
</table></div>
<h6>
<a name="geometry.reference.algorithms.union_.h6"></a>
<span class="phrase"><a name="geometry.reference.algorithms.union_.example"></a></span><a class="link" href="union_.html#geometry.reference.algorithms.union_.example">Example</a>
</h6>
<p>
Shows how to get a united geometry of two polygons
</p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">vector</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">/</span><span class="identifier">geometries</span><span class="special">/</span><span class="identifier">point_xy</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">/</span><span class="identifier">geometries</span><span class="special">/</span><span class="identifier">polygon</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">foreach</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
<span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">model</span><span class="special">::</span><span class="identifier">polygon</span><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">model</span><span class="special">::</span><span class="identifier">d2</span><span class="special">::</span><span class="identifier">point_xy</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">&gt;</span> <span class="special">&gt;</span> <span class="identifier">polygon</span><span class="special">;</span>
<span class="identifier">polygon</span> <span class="identifier">green</span><span class="special">,</span> <span class="identifier">blue</span><span class="special">;</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">read_wkt</span><span class="special">(</span>
<span class="string">"POLYGON((2 1.3,2.4 1.7,2.8 1.8,3.4 1.2,3.7 1.6,3.4 2,4.1 3,5.3 2.6,5.4 1.2,4.9 0.8,2.9 0.7,2 1.3)"</span>
<span class="string">"(4.0 2.0, 4.2 1.4, 4.8 1.9, 4.4 2.2, 4.0 2.0))"</span><span class="special">,</span> <span class="identifier">green</span><span class="special">);</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">read_wkt</span><span class="special">(</span>
<span class="string">"POLYGON((4.0 -0.5 , 3.5 1.0 , 2.0 1.5 , 3.5 2.0 , 4.0 3.5 , 4.5 2.0 , 6.0 1.5 , 4.5 1.0 , 4.0 -0.5))"</span><span class="special">,</span> <span class="identifier">blue</span><span class="special">);</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">polygon</span><span class="special">&gt;</span> <span class="identifier">output</span><span class="special">;</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">union_</span><span class="special">(</span><span class="identifier">green</span><span class="special">,</span> <span class="identifier">blue</span><span class="special">,</span> <span class="identifier">output</span><span class="special">);</span>
<span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"green || blue:"</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
<span class="identifier">BOOST_FOREACH</span><span class="special">(</span><span class="identifier">polygon</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">p</span><span class="special">,</span> <span class="identifier">output</span><span class="special">)</span>
<span class="special">{</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">i</span><span class="special">++</span> <span class="special">&lt;&lt;</span> <span class="string">": "</span> <span class="special">&lt;&lt;</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">area</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
<span class="special">}</span>
<span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
</p>
<p>
Output:
</p>
<pre class="programlisting">green || blue:
0: 5.64795
<img src="../../../img/algorithms/union.png" alt="union">
</pre>
<h6>
<a name="geometry.reference.algorithms.union_.h7"></a>
<span class="phrase"><a name="geometry.reference.algorithms.union_.see_also"></a></span><a class="link" href="union_.html#geometry.reference.algorithms.union_.see_also">See
also</a>
</h6>
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<li class="listitem">
<a class="link" href="intersection.html" title="intersection">intersection</a>
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<a class="link" href="difference.html" title="difference">difference</a>
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<a class="link" href="sym_difference.html" title="sym_difference">sym_difference
(symmetric difference)</a>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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