c++ - Boost.Geometry 多边形点赋值

Question

我正在尝试使用增强几何并且无法将点分配给多边形。假设我创建了一个静态的点向量

boost::geometry::model::d2::point_xy<double> >* a; 

然后我创建一个多边形：

boost::geometry::model::polygon<boost::geometry::model::d2::point_xy<double> > polygon;

假设我已经定义了 a 点的值。

如何将点从 a 分配给 P？

Answer 1

The boost::geometry::assign_points() algorithm can be used to assign a range of points to a polygon.

If a is a range of points and P is a polygon, then one would use:

boost::geometry::assign_points(P, a);

---

Here is a complete example demonstrating the usage of assign_points:

#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;
}

Which produces the following output:

Polygon (((0, 0), (0, 5), (5, 5), (5, 0), (0, 0))) has an area of 25