boost C++library 如何将需要的坐标全部加入到polygon内

 #include <iostream>
#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#include <boost/geometry/geometries/box.hpp>
#include <boost/geometry/geometries/polygon.hpp>
#include <boost/assign/list_of.hpp>
#include <string>
namespace bg = boost::geometry;

int main()
{
      std::string a = "(0, 0)(0, 3)(3, 3)(0, 0)";
    typedef bg::model::d2::point_xy<double> point;
    typedef bg::model::box<point> box;
    typedef bg::model::polygon<point> polygon;

//    // box
//    {
//        const box x(point(0, 0), point(3, 3));
//
//        const double result = bg::area(x);
//        std::cout << result << std::endl;
//    }
    // polygon

        polygon x;
        bg::exterior_ring(x) = boost::assign::list_of<point>a;

        const double result = bg::area(x);
        std::cout << result << std::endl;

}

include <iostream>
#include <vector>
#include <boost/assign/std/vector.hpp>
#include <boost/geometry.hpp>
#include <boost/geometry/algorithms/area.hpp>
#include <boost/geometry/algorithms/assign.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#include <boost/geometry/geometries/polygon.hpp>
#include <boost/geometry/io/dsv/write.hpp>

int main()
{
    using namespace boost::assign;
    typedef boost::geometry::model::d2::point_xy<double> point_xy;

    // Create points to represent a 5x5 closed polygon.
    std::vector<point_xy> points;
    points +=
      point_xy(0,0),
      point_xy(0,5),
      point_xy(5,5),
      point_xy(5,0),
      point_xy(0,0)
      ;

    // Create a polygon object and assign the points to it.
    boost::geometry::model::polygon<point_xy> polygon;  
    boost::geometry::assign_points(polygon, points);

    std::cout << "Polygon " << boost::geometry::dsv(polygon) << 
      " has an area of " << boost::geometry::area(polygon) << std::endl;
}