model::multi_polygon

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#### model::multi_polygon

multi_polygon, a collection of polygons

###### Description

Multi-polygon can be used to group polygons belonging to each other, e.g. Hawaii

###### Model of

MultiPolygon Concept

###### Synopsis

    template<typename Polygon, template< typename, typename > class Container, template< typename > class Allocator>
    class model::multi_polygon
          : public Container< Polygon, Allocator< Polygon > >
    {
      // ...
    };

###### Template parameter(s)

Parameter | Default | Description
--- | --- | ---
typename Polygon |  |
template< typename, typename > class Container | std::vector |
template< typename > class Allocator | std::allocator |

###### Constructor(s)

Function | Description | Parameters
--- | --- | ---

    multi_polygon()

Default constructor, creating an empty multi_polygon.

    multi_polygon(std::initializer_list< Polygon > l)

Constructor taking std::initializer_list, filling the multi_polygon.

std::initializer_list< Polygon >: l:

###### Header

Either

`#include <boost/geometry/geometries/geometries.hpp>`

Or

`#include <boost/geometry/geometries/multi_polygon.hpp>`

###### Examples

Declaration and use of the Boost.Geometry model::multi_polygon, modelling the MultiPolygon Concept

    #include <iostream>
    #include <boost/geometry.hpp>
    #include <boost/geometry/geometries/geometries.hpp>

    namespace bg = boost::geometry;

    int main()
    {
        typedef bg::model::point<double, 2, bg::cs::cartesian> point_t;
        typedef bg::model::polygon<point_t> polygon_t;
        typedef bg::model::multi_polygon<polygon_t> mpolygon_t;

        mpolygon_t mpoly1;

    #if !defined(BOOST_NO_CXX11_UNIFIED_INITIALIZATION_SYNTAX) \
     && !defined(BOOST_NO_CXX11_HDR_INITIALIZER_LIST)

        mpolygon_t mpoly2{{{{0.0, 0.0}, {0.0, 5.0}, {5.0, 5.0}, {5.0, 0.0}, {0.0, 0.0}},
                           {{1.0, 1.0}, {4.0, 1.0}, {4.0, 4.0}, {1.0, 4.0}, {1.0, 1.0}}},
                          {{{5.0, 5.0}, {5.0, 6.0}, {6.0, 6.0}, {6.0, 5.0}, {5.0, 5.0}}}};

    #endif

        mpoly1.resize(2);

        bg::append(mpoly1[0].outer(), point_t(0.0, 0.0));
        bg::append(mpoly1[0].outer(), point_t(0.0, 5.0));
        bg::append(mpoly1[0].outer(), point_t(5.0, 5.0));
        bg::append(mpoly1[0].outer(), point_t(5.0, 0.0));
        bg::append(mpoly1[0].outer(), point_t(0.0, 0.0));

        mpoly1[0].inners().resize(1);
        bg::append(mpoly1[0].inners()[0], point_t(1.0, 1.0));
        bg::append(mpoly1[0].inners()[0], point_t(4.0, 1.0));
        bg::append(mpoly1[0].inners()[0], point_t(4.0, 4.0));
        bg::append(mpoly1[0].inners()[0], point_t(1.0, 4.0));
        bg::append(mpoly1[0].inners()[0], point_t(1.0, 1.0));

        bg::append(mpoly1[1].outer(), point_t(5.0, 5.0));
        bg::append(mpoly1[1].outer(), point_t(5.0, 6.0));
        bg::append(mpoly1[1].outer(), point_t(6.0, 6.0));
        bg::append(mpoly1[1].outer(), point_t(6.0, 5.0));
        bg::append(mpoly1[1].outer(), point_t(5.0, 5.0));

        double a = bg::area(mpoly1);

        std::cout << a << std::endl;

        return 0;
    }

| Default parameters, clockwise, closed polygon.
| Clockwise, closed multi_polygon.
| Default-construct a multi_polygon.
| Construct a multi_polygon containing two polygons, using C++11 unified initialization syntax.
| Resize a multi_polygon, store two polygons.
| Append point to the exterior ring of the first polygon.
| Resize a container of interior rings of the first polygon.
| Append point to the interior ring of the first polygon.
| Append point to the exterior ring of the second polygon.

Output:

    17