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<div class="titlepage"><div><div><h5 class="title">
<a name="geometry.reference.algorithms.centroid.centroid_2"></a><a class="link" href="centroid_2.html" title="centroid">centroid</a>
</h5></div></div></div>
<p>
<a class="indexterm" name="id838274"></a>
Calculates the centroid of a geometry.
</p>
<a name="geometry.reference.algorithms.centroid.centroid_2.description"></a><h6>
<a name="geometry.reference.algorithms.centroid.centroid_2.description-heading"></a>
<a class="link" href="centroid_2.html#geometry.reference.algorithms.centroid.centroid_2.description">Description</a>
</h6>
<p>
The free function centroid calculates the geometric center (or: center
of mass) of a geometry. It uses the default strategy, based on the coordinate
system of the geometry.
</p>
<a name="geometry.reference.algorithms.centroid.centroid_2.synopsis"></a><h6>
<a name="geometry.reference.algorithms.centroid.centroid_2.synopsis-heading"></a>
<a class="link" href="centroid_2.html#geometry.reference.algorithms.centroid.centroid_2.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">Geometry</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Point</span><span class="special">&gt;</span>
<span class="keyword">void</span> <span class="identifier">centroid</span><span class="special">(</span><span class="identifier">Geometry</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="identifier">geometry</span><span class="special">,</span> <span class="identifier">Point</span> <span class="special">&amp;</span> <span class="identifier">c</span><span class="special">)</span></pre>
<p>
</p>
<a name="geometry.reference.algorithms.centroid.centroid_2.parameters"></a><h6>
<a name="geometry.reference.algorithms.centroid.centroid_2.parameters-heading"></a>
<a class="link" href="centroid_2.html#geometry.reference.algorithms.centroid.centroid_2.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>
Geometry const &amp;
</p>
</td>
<td>
<p>
Any type fulfilling a Geometry Concept
</p>
</td>
<td>
<p>
geometry
</p>
</td>
<td>
<p>
A model of the specified concept
</p>
</td>
</tr>
<tr>
<td>
<p>
Point &amp;
</p>
</td>
<td>
<p>
Any type fulfilling a Point Concept
</p>
</td>
<td>
<p>
c
</p>
</td>
<td>
<p>
The calculated centroid will be assigned to this point reference
</p>
</td>
</tr>
</tbody>
</table></div>
<a name="geometry.reference.algorithms.centroid.centroid_2.header"></a><h6>
<a name="geometry.reference.algorithms.centroid.centroid_2.header-heading"></a>
<a class="link" href="centroid_2.html#geometry.reference.algorithms.centroid.centroid_2.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">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="identifier">centroid</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
</p>
<a name="geometry.reference.algorithms.centroid.centroid_2.behavior"></a><h6>
<a name="geometry.reference.algorithms.centroid.centroid_2.behavior-heading"></a>
<a class="link" href="centroid_2.html#geometry.reference.algorithms.centroid.centroid_2.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>
Point
</p>
</td>
<td>
<p>
Returns the point itself as the centroid
</p>
</td>
</tr>
<tr>
<td>
<p>
Multi Point
</p>
</td>
<td>
<p>
Calculates centroid (based on average)
</p>
</td>
</tr>
<tr>
<td>
<p>
linear (e.g. linestring)
</p>
</td>
<td>
<p>
Calculates centroid (based on weighted length)
</p>
</td>
</tr>
<tr>
<td>
<p>
areal (e.g. polygon)
</p>
</td>
<td>
<p>
Calculates centroid
</p>
</td>
</tr>
<tr>
<td>
<p>
Empty (e.g. polygon without points)
</p>
</td>
<td>
<p>
Throws a <a class="link" href="../../exceptions/centroid_exception.html" title="centroid_exception">centroid_exception</a>
</p>
</td>
</tr>
<tr>
<td>
<p>
Cartesian
</p>
</td>
<td>
<p>
Implemented
</p>
</td>
</tr>
<tr>
<td>
<p>
Spherical
</p>
</td>
<td>
<p>
Calculates the centroid as if based on Cartesian coordinates
</p>
</td>
</tr>
</tbody>
</table></div>
<a name="geometry.reference.algorithms.centroid.centroid_2.supported_geometries"></a><h6>
<a name="geometry.reference.algorithms.centroid.centroid_2.supported_geometries-heading"></a>
<a class="link" href="centroid_2.html#geometry.reference.algorithms.centroid.centroid_2.supported_geometries">Supported
geometries</a>
</h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
</th>
<th>
<p>
2D
</p>
</th>
<th>
<p>
3D
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
Point
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
</p>
</td>
</tr>
<tr>
<td>
<p>
Segment
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
</p>
</td>
</tr>
<tr>
<td>
<p>
Box
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
</p>
</td>
</tr>
<tr>
<td>
<p>
Linestring
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/nyi.png" alt="nyi"></span>
</p>
</td>
</tr>
<tr>
<td>
<p>
Ring
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/nyi.png" alt="nyi"></span>
</p>
</td>
</tr>
<tr>
<td>
<p>
Polygon
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/nyi.png" alt="nyi"></span>
</p>
</td>
</tr>
<tr>
<td>
<p>
MultiPoint
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
</p>
</td>
</tr>
<tr>
<td>
<p>
MultiLinestring
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/nyi.png" alt="nyi"></span>
</p>
</td>
</tr>
<tr>
<td>
<p>
MultiPolygon
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/nyi.png" alt="nyi"></span>
</p>
</td>
</tr>
</tbody>
</table></div>
<a name="geometry.reference.algorithms.centroid.centroid_2.complexity"></a><h6>
<a name="geometry.reference.algorithms.centroid.centroid_2.complexity-heading"></a>
<a class="link" href="centroid_2.html#geometry.reference.algorithms.centroid.centroid_2.complexity">Complexity</a>
</h6>
<p>
Linear
</p>
<a name="geometry.reference.algorithms.centroid.centroid_2.example"></a><h6>
<a name="geometry.reference.algorithms.centroid.centroid_2.example-heading"></a>
<a class="link" href="centroid_2.html#geometry.reference.algorithms.centroid.centroid_2.example">Example</a>
</h6>
<p>
Shows calculation of a centroid of a polygon
</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">list</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">geometry</span><span class="special">/</span><span class="identifier">domains</span><span class="special">/</span><span class="identifier">gis</span><span class="special">/</span><span class="identifier">io</span><span class="special">/</span><span class="identifier">wkt</span><span class="special">/</span><span class="identifier">wkt</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">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="identifier">point_type</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">point_type</span><span class="special">&gt;</span> <span class="identifier">polygon_type</span><span class="special">;</span>
<span class="identifier">polygon_type</span> <span class="identifier">poly</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">poly</span><span class="special">);</span>
<span class="identifier">point_type</span> <span class="identifier">p</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">centroid</span><span class="special">(</span><span class="identifier">poly</span><span class="special">,</span> <span class="identifier">p</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">"centroid: "</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">dsv</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="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">centroid: (4.04663, 1.6349)
<img src="../../../../img/algorithms/centroid.png" alt="centroid">
</pre>
<p>
Note that the centroid might be located in a hole or outside a polygon,
easily.
</p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2011 Barend Gehrels, Bruno Lalande, Mateusz Loskot<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
</p>
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