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<div class="titlepage"><div><div><h5 class="title">
<a name="geometry.reference.algorithms.area.area_1"></a><a class="link" href="area_1.html" title="area">area</a>
</h5></div></div></div>
<p>
<a class="indexterm" name="id820610"></a>
Calculates the area of a geometry.
</p>
<a name="geometry.reference.algorithms.area.area_1.description"></a><h6>
<a name="geometry.reference.algorithms.area.area_1.description-heading"></a>
<a class="link" href="area_1.html#geometry.reference.algorithms.area.area_1.description">Description</a>
</h6>
<p>
The free function area calculates the area of a geometry. It uses the
default strategy, based on the coordinate system of the geometry.
</p>
<p>
The area algorithm calculates the surface area of all geometries having
a surface, namely box, polygon, ring, multipolygon. The units are the
square of the units used for the points defining the surface. If subject
geometry is defined in meters, then area is calculated in square meters.
</p>
<p>
The area calculation can be done in all three common coordinate systems,
Cartesian, Spherical and Geographic as well.
</p>
<a name="geometry.reference.algorithms.area.area_1.synopsis"></a><h6>
<a name="geometry.reference.algorithms.area.area_1.synopsis-heading"></a>
<a class="link" href="area_1.html#geometry.reference.algorithms.area.area_1.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">&gt;</span>
<span class="identifier">default_area_result</span><span class="special">&lt;</span><span class="identifier">Geometry</span><span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">area</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></pre>
<p>
</p>
<a name="geometry.reference.algorithms.area.area_1.parameters"></a><h6>
<a name="geometry.reference.algorithms.area.area_1.parameters-heading"></a>
<a class="link" href="area_1.html#geometry.reference.algorithms.area.area_1.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></tbody>
</table></div>
<a name="geometry.reference.algorithms.area.area_1.returns"></a><h6>
<a name="geometry.reference.algorithms.area.area_1.returns-heading"></a>
<a class="link" href="area_1.html#geometry.reference.algorithms.area.area_1.returns">Returns</a>
</h6>
<p>
The calculated area
</p>
<a name="geometry.reference.algorithms.area.area_1.header"></a><h6>
<a name="geometry.reference.algorithms.area.area_1.header-heading"></a>
<a class="link" href="area_1.html#geometry.reference.algorithms.area.area_1.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">area</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
</p>
<a name="geometry.reference.algorithms.area.area_1.behavior"></a><h6>
<a name="geometry.reference.algorithms.area.area_1.behavior-heading"></a>
<a class="link" href="area_1.html#geometry.reference.algorithms.area.area_1.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>
pointlike (e.g. point)
</p>
</td>
<td>
<p>
Returns 0
</p>
</td>
</tr>
<tr>
<td>
<p>
linear (e.g. linestring)
</p>
</td>
<td>
<p>
Returns 0
</p>
</td>
</tr>
<tr>
<td>
<p>
areal (e.g. polygon)
</p>
</td>
<td>
<p>
Returns the area
</p>
</td>
</tr>
<tr>
<td>
<p>
Cartesian
</p>
</td>
<td>
<p>
Returns the area in the same units as the input coordinates
</p>
</td>
</tr>
<tr>
<td>
<p>
Spherical
</p>
</td>
<td>
<p>
Returns the area on a unit sphere (or another sphere, if specified
as such in the constructor of the strategy)
</p>
</td>
</tr>
<tr>
<td>
<p>
Reversed polygon (coordinates not according their orientiation)
</p>
</td>
<td>
<p>
Returns the negative area
</p>
</td>
</tr>
</tbody>
</table></div>
<a name="geometry.reference.algorithms.area.area_1.supported_geometries"></a><h6>
<a name="geometry.reference.algorithms.area.area_1.supported_geometries-heading"></a>
<a class="link" href="area_1.html#geometry.reference.algorithms.area.area_1.supported_geometries">Supported
geometries</a>
</h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Geometry
</p>
</th>
<th>
<p>
Status
</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>
</tr>
<tr>
<td>
<p>
Segment
</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>
</tr>
<tr>
<td>
<p>
Linestring
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></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>
</tr>
<tr>
<td>
<p>
Polygon
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></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>
</tr>
<tr>
<td>
<p>
MultiLinestring
</p>
</td>
<td>
<p>
<span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></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>
</tr>
</tbody>
</table></div>
<a name="geometry.reference.algorithms.area.area_1.complexity"></a><h6>
<a name="geometry.reference.algorithms.area.area_1.complexity-heading"></a>
<a class="link" href="area_1.html#geometry.reference.algorithms.area.area_1.complexity">Complexity</a>
</h6>
<p>
Linear
</p>
<a name="geometry.reference.algorithms.area.area_1.examples"></a><h6>
<a name="geometry.reference.algorithms.area.area_1.examples-heading"></a>
<a class="link" href="area_1.html#geometry.reference.algorithms.area.area_1.examples">Examples</a>
</h6>
<p>
Calculate the area 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">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">namespace</span> <span class="identifier">bg</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">;</span> <a class="co" name="geometry4co" href="area_1.html#geometry4"><img src="../../../../../../../../doc/src/images/callouts/1.png" alt="1" border="0"></a>
<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
<span class="comment">// Calculate the area of a cartesian polygon</span>
<span class="identifier">bg</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">bg</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">poly</span><span class="special">;</span>
<span class="identifier">bg</span><span class="special">::</span><span class="identifier">read_wkt</span><span class="special">(</span><span class="string">"POLYGON((0 0,0 7,4 2,2 0,0 0))"</span><span class="special">,</span> <span class="identifier">poly</span><span class="special">);</span>
<span class="keyword">double</span> <span class="identifier">area</span> <span class="special">=</span> <span class="identifier">bg</span><span class="special">::</span><span class="identifier">area</span><span class="special">(</span><span class="identifier">poly</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">"Area: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">area</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="comment">// Calculate the area of a spherical equatorial polygon</span>
<span class="identifier">bg</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">bg</span><span class="special">::</span><span class="identifier">model</span><span class="special">::</span><span class="identifier">point</span><span class="special">&lt;</span><span class="keyword">float</span><span class="special">,</span> <span class="number">2</span><span class="special">,</span> <span class="identifier">bg</span><span class="special">::</span><span class="identifier">cs</span><span class="special">::</span><span class="identifier">spherical_equatorial</span><span class="special">&lt;</span><span class="identifier">bg</span><span class="special">::</span><span class="identifier">degree</span><span class="special">&gt;</span> <span class="special">&gt;</span> <span class="special">&gt;</span> <span class="identifier">sph_poly</span><span class="special">;</span>
<span class="identifier">bg</span><span class="special">::</span><span class="identifier">read_wkt</span><span class="special">(</span><span class="string">"POLYGON((0 0,0 45,45 0,0 0))"</span><span class="special">,</span> <span class="identifier">sph_poly</span><span class="special">);</span>
<span class="identifier">area</span> <span class="special">=</span> <span class="identifier">bg</span><span class="special">::</span><span class="identifier">area</span><span class="special">(</span><span class="identifier">sph_poly</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">"Area: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">area</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>
<div class="calloutlist"><table border="0" summary="Callout list"><tr>
<td width="5%" valign="top" align="left"><p><a name="geometry4"></a><a href="#geometry4co"><img src="../../../../../../../../doc/src/images/callouts/1.png" alt="1" border="0"></a> </p></td>
<td valign="top" align="left"><p>
Convenient namespace alias
</p></td>
</tr></table></div>
<p>
Output:
</p>
<pre class="programlisting">Area: 16
Area: 0.339837
</pre>
</div>
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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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