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<title>length (with strategy)</title>
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<div class="titlepage"><div><div><h5 class="title">
<a name="geometry.reference.algorithms.length.length_2_with_strategy"></a><a class="link" href="length_2_with_strategy.html" title="length (with strategy)">length
(with strategy)</a>
</h5></div></div></div>
<p>
<a class="indexterm" name="id876597"></a>
Calculates the length of a geometry using the specified strategy.
</p>
<a name="geometry.reference.algorithms.length.length_2_with_strategy.description"></a><h6>
<a name="geometry.reference.algorithms.length.length_2_with_strategy.description-heading"></a>
<a class="link" href="length_2_with_strategy.html#geometry.reference.algorithms.length.length_2_with_strategy.description">Description</a>
</h6>
<p>
The free function length calculates the length (the sum of distances
between consecutive points) of a geometry using the specified strategy.
Reasons to specify a strategy include: use another coordinate system
for calculations; construct the strategy beforehand (e.g. with the radius
of the Earth); select a strategy when there are more than one available
for a calculation.
</p>
<a name="geometry.reference.algorithms.length.length_2_with_strategy.synopsis"></a><h6>
<a name="geometry.reference.algorithms.length.length_2_with_strategy.synopsis-heading"></a>
<a class="link" href="length_2_with_strategy.html#geometry.reference.algorithms.length.length_2_with_strategy.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">Strategy</span><span class="special">&gt;</span>
<span class="identifier">default_length_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">length</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">Strategy</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="identifier">strategy</span><span class="special">)</span></pre>
<p>
</p>
<a name="geometry.reference.algorithms.length.length_2_with_strategy.parameters"></a><h6>
<a name="geometry.reference.algorithms.length.length_2_with_strategy.parameters-heading"></a>
<a class="link" href="length_2_with_strategy.html#geometry.reference.algorithms.length.length_2_with_strategy.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>
Strategy const &amp;
</p>
</td>
<td>
<p>
Any type fulfilling a distance Strategy Concept
</p>
</td>
<td>
<p>
strategy
</p>
</td>
<td>
<p>
The strategy which will be used for distance calculations
</p>
</td>
</tr>
</tbody>
</table></div>
<a name="geometry.reference.algorithms.length.length_2_with_strategy.returns"></a><h6>
<a name="geometry.reference.algorithms.length.length_2_with_strategy.returns-heading"></a>
<a class="link" href="length_2_with_strategy.html#geometry.reference.algorithms.length.length_2_with_strategy.returns">Returns</a>
</h6>
<p>
The calculated length
</p>
<a name="geometry.reference.algorithms.length.length_2_with_strategy.header"></a><h6>
<a name="geometry.reference.algorithms.length.length_2_with_strategy.header-heading"></a>
<a class="link" href="length_2_with_strategy.html#geometry.reference.algorithms.length.length_2_with_strategy.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">length</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
</p>
<a name="geometry.reference.algorithms.length.length_2_with_strategy.behavior"></a><h6>
<a name="geometry.reference.algorithms.length.length_2_with_strategy.behavior-heading"></a>
<a class="link" href="length_2_with_strategy.html#geometry.reference.algorithms.length.length_2_with_strategy.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 the length
</p>
</td>
</tr>
<tr>
<td>
<p>
areal (e.g. polygon)
</p>
</td>
<td>
<p>
Returns 0
</p>
</td>
</tr>
</tbody>
</table></div>
<a name="geometry.reference.algorithms.length.length_2_with_strategy.complexity"></a><h6>
<a name="geometry.reference.algorithms.length.length_2_with_strategy.complexity-heading"></a>
<a class="link" href="length_2_with_strategy.html#geometry.reference.algorithms.length.length_2_with_strategy.complexity">Complexity</a>
</h6>
<p>
Linear
</p>
<a name="geometry.reference.algorithms.length.length_2_with_strategy.examples"></a><h6>
<a name="geometry.reference.algorithms.length.length_2_with_strategy.examples-heading"></a>
<a class="link" href="length_2_with_strategy.html#geometry.reference.algorithms.length.length_2_with_strategy.examples">Examples</a>
</h6>
<p>
The following example shows the length measured over a sphere, expressed
in kilometers. To do that the radius of the sphere must be specified
in the constructor of the strategy.
</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">linestring</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">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">;</span>
<span class="keyword">typedef</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">cs</span><span class="special">::</span><span class="identifier">spherical_equatorial</span><span class="special">&lt;</span><span class="identifier">degree</span><span class="special">&gt;</span> <span class="special">&gt;</span> <span class="identifier">P</span><span class="special">;</span>
<span class="identifier">model</span><span class="special">::</span><span class="identifier">linestring</span><span class="special">&lt;</span><span class="identifier">P</span><span class="special">&gt;</span> <span class="identifier">line</span><span class="special">;</span>
<span class="identifier">line</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">P</span><span class="special">(</span><span class="number">2</span><span class="special">,</span> <span class="number">41</span><span class="special">));</span>
<span class="identifier">line</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">P</span><span class="special">(</span><span class="number">2</span><span class="special">,</span> <span class="number">48</span><span class="special">));</span>
<span class="identifier">line</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">P</span><span class="special">(</span><span class="number">5</span><span class="special">,</span> <span class="number">52</span><span class="special">));</span>
<span class="keyword">double</span> <span class="keyword">const</span> <span class="identifier">mean_radius</span> <span class="special">=</span> <span class="number">6371.0</span><span class="special">;</span> <a class="co" name="geometry12co" href="length_2_with_strategy.html#geometry12"><img src="../../../../../../../../doc/src/images/callouts/1.png" alt="1" border="0"></a>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"length is "</span>
<span class="special">&lt;&lt;</span> <span class="identifier">length</span><span class="special">(</span><span class="identifier">line</span><span class="special">,</span> <span class="identifier">strategy</span><span class="special">::</span><span class="identifier">distance</span><span class="special">::</span><span class="identifier">haversine</span><span class="special">&lt;</span><span class="identifier">P</span><span class="special">&gt;(</span><span class="identifier">mean_radius</span><span class="special">)</span> <span class="special">)</span>
<span class="special">&lt;&lt;</span> <span class="string">" kilometers "</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="geometry12"></a><a href="#geometry12co"><img src="../../../../../../../../doc/src/images/callouts/1.png" alt="1" border="0"></a> </p></td>
<td valign="top" align="left"><p>
<a href="http://en.wikipedia.org/wiki/Earth_radius" target="_top">Wiki</a>
</p></td>
</tr></table></div>
<p>
Output:
</p>
<pre class="programlisting">length is 1272.03 kilometers
</pre>
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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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