如何从Boost Envelope中获得最小边界矩形的所有四个角？

#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point.hpp>
#include <boost/geometry/geometries/box.hpp>

typedef boost::geometry::model::d2::point_xy<double> point_type;
typedef boost::geometry::model::box<point_type> box_type;
typedef boost::geometry::model::polygon<point_type> polygon_type;

polygon_type polygon;

boost::geometry::envelope(polygon, envelope);

const auto& outer_ring = polygon.outer();

const auto& first_point = outer_ring.front();
const auto& last_point = outer_ring.back();
const auto& second_point = outer_ring[1];
const auto& third_point = outer_ring[2];