...one of the most highly
regarded and expertly designed C++ library projects in the
world.

— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards

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/geometry.hpp>`

Or

`#include <boost/geometry/algorithms/length.hpp>`

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<P>(mean_radius) ) << " kilometers " << std::endl; return 0; }

Output:

length is 1272.03 kilometers