# Boost C++ Libraries

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

##### discrete_frechet_distance

Calculate discrete Frechet distance between two geometries (currently work for LineString-LineString).

###### Synopsis

```template<typename Geometry1, typename Geometry2>
auto discrete_frechet_distance(Geometry1 const & geometry1, Geometry2 const & geometry2)```

###### Parameters

Type

Concept

Name

Description

Geometry1 const &

Any type fulfilling a Geometry Concept

geometry1

Input geometry

Geometry2 const &

Any type fulfilling a Geometry Concept

geometry2

Input geometry

Either

`#include <boost/geometry.hpp>`

Or

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

###### Behavior

The algorithm calculate discrete frechet distance between two geometries.

Note The units of the distance depends on strategy. In order to change the default behavior a user has to create a strategy and pass it explicitly into the algorithm.
###### Example

Calculate Similarity between two geometries as the discrete frechet distance between them.

```#include <iostream>

#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#include <boost/geometry/geometries/linestring.hpp>

int main()
{
typedef boost::geometry::model::d2::point_xy<double> point_type;
typedef boost::geometry::model::linestring<point_type> linestring_type;

linestring_type ls1, ls2;
boost::geometry::read_wkt("LINESTRING(0 0,1 1,1 2,2 1,2 2)", ls1);
boost::geometry::read_wkt("LINESTRING(1 0,0 1,1 1,2 1,3 1)", ls2);

double res = boost::geometry::discrete_frechet_distance(ls1, ls2);

std::cout << "Discrete Frechet Distance: " << res << std::endl;

return 0;
}
```

Output:

```Discrete Frechet Distance:  1.41421
```