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Calculates the length of a geometry using the specified strategy.
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.
template<typename Geometry, typename Strategy> default_length_result<Geometry>::type length(Geometry const & geometry, Strategy const & strategy)
| Type | Concept | Name | Description | 
|---|---|---|---|
| Geometry const & | Any type fulfilling a Geometry Concept | geometry | A model of the specified concept | 
| Strategy const & | Any type fulfilling a distance Strategy Concept | strategy | The strategy which will be used for distance calculations | 
The calculated length
Either
            #include <boost/geometry.hpp>
          
Or
            #include <boost/geometry/algorithms/length.hpp>
          
The function length implements function Length from the OGC Simple Feature Specification.
| Case | Behavior | 
|---|---|
| pointlike (e.g. point) | Returns 0 | 
| linear (e.g. linestring) | Returns the length | 
| areal (e.g. polygon) | Returns 0 | 
Linear
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.
#include <iostream> #include <boost/geometry.hpp> #include <boost/geometry/geometries/linestring.hpp> int main() { using namespace boost::geometry; typedef model::point<float, 2, cs::spherical_equatorial<degree> > P; model::linestring<P> line; line.push_back(P(2, 41)); line.push_back(P(2, 48)); line.push_back(P(5, 52)); double const mean_radius = 6371.0;std::cout << "length is " << length(line, strategy::distance::haversine<float>(mean_radius) ) << " kilometers " << std::endl; return 0; }
Output:
length is 1272.03 kilometers