Boost C++ Libraries

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for_each_point

Applies function f to each point.

Description

Applies a function f (functor, having operator() defined) to each point making up the geometry

Synopsis

```template<typename Geometry, typename Functor>
Functor for_each_point(Geometry & geometry, Functor f)```

Parameters

Type

Concept

Name

Description

Geometry &

Any type fulfilling a Geometry Concept

geometry

A model of the specified concept

Functor

Function or class with operator()

f

Unary function, taking a point as argument

Either

`#include <boost/geometry.hpp>`

Or

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

Conformance

The function for_each_point is not defined by OGC.

The function for_each_point conforms to the std::for_each function of the C++ std-library.

Example

Convenient usage of for_each_point, rounding all points of a geometry

```#include <iostream>

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

template <typename Point>
class round_coordinates
{
private :
typedef typename boost::geometry::coordinate_type<Point>::type coordinate_type;
coordinate_type factor;

inline coordinate_type round(coordinate_type value)
{
return floor(0.5 + (value / factor)) * factor;
}

public :
round_coordinates(coordinate_type f)
: factor(f)
{}

inline void operator()(Point& p)
{
using boost::geometry::get;
using boost::geometry::set;
set<0>(p, round(get<0>(p)));
set<1>(p, round(get<1>(p)));
}
};

int main()
{
typedef boost::geometry::model::d2::point_xy<double> point;
boost::geometry::model::polygon<point> poly;
boost::geometry::read_wkt("POLYGON((0 0,1.123 9.987,8.876 2.234,0 0),(3.345 4.456,7.654 8.765,9.123 5.432,3.345 4.456))", poly);
boost::geometry::for_each_point(poly, round_coordinates<point>(0.1));
std::cout << "Rounded: " << boost::geometry::wkt(poly) << std::endl;
return 0;
}
```

Output:

```Rounded: POLYGON((0 0,1.1 10,8.9 2.2,0 0),(3.3 4.5,7.7 8.8,9.1 5.4,3.3 4.5))
```

Sample using for_each_point, using a function to list coordinates

```#include <iostream>

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

template <typename Point>
void list_coordinates(Point const& p)
{
using boost::geometry::get;
std::cout << "x = " << get<0>(p) << " y = " << get<1>(p) << std::endl;
}

int main()
{
typedef boost::geometry::model::d2::point_xy<double> point;
boost::geometry::model::polygon<point> poly;
boost::geometry::read_wkt("POLYGON((0 0,0 4,4 0,0 0))", poly);
boost::geometry::for_each_point(poly, list_coordinates<point>);
return 0;
}
```

Output:

```x = 0 y = 0
x = 0 y = 4
x = 4 y = 0
x = 0 y = 0
```