使用 boost 几何找到线段的交点

Question

我正在尝试将 boost 几何方法 intersects 与我自己的点类一起使用，成功注册到 boost 几何库。

boost 文档 (https://www.boost.org/doc/libs/1_73_0/libs/geometry/doc/html/geometry/reference/algorithms/intersection/intersection_3.html) 说我可以使用点向量作为输出参数。所以我写了这个：

#include <iostream>
#include <deque>
#include <boost/geometry.hpp>
#include <boost/geometry/geometries/register/point.hpp>

namespace bg = boost::geometry;
using namespace std;

class cxy
{
public:
    double x;
    double y;
    cxy( double X, double Y )
        : x( X )
        , y( Y )
    {

    }
    /// boost geometry insists on a default constructor
    cxy()
        : cxy(0,0)
    {

    }
};

BOOST_GEOMETRY_REGISTER_POINT_2D( cxy, double, bg::cs::cartesian, x, y )
typedef bg::model::segment<cxy> segment_t;

int main()
{
    cxy a(0,0);
    cxy b(1,1);
    cxy c(1,0);
    cxy d(0,1) ;

    std::vector<cxy> out;

    //////////////// this compiles

    bg::intersection(segment_t{a, b}, segment_t{c, d}, out);

    //////////////// this does not!!!

    segment_t ab( a, b );
    segment_t cd( c, d );
    bg::intersects( ab, cd, out );

    return 0;
}

要明确：我的问题是我在 intersection 和 intersects 之间感到困惑

以下代码编译并产生预期的结果：

#include <iostream>
#include <deque>
#include <boost/geometry.hpp>
#include <boost/geometry/geometries/register/point.hpp>

namespace bg = boost::geometry;
using namespace std;

class cxy
{
public:
    double x;
    double y;
    cxy( double X, double Y )
        : x( X )
        , y( Y )
    {

    }
    /// boost geometry insists on a default constructor
    cxy()
        : cxy(0,0)
    {

    }
};

BOOST_GEOMETRY_REGISTER_POINT_2D( cxy, double, bg::cs::cartesian, x, y )
typedef bg::model::segment<cxy> segment_t;

int main()
{
    cxy a(0,0);
    cxy b(1,1);
    cxy c(1,0);
    cxy d(0,1) ;

    segment_t ab( a, b );
    segment_t cd( c, d );
    std::vector<cxy> out;
    if( ! bg::intersection( ab, cd, out ) ) {
       std::cout << "no intersection\n";
       return 1;
    }
    std::cout << "intersection at " << out[0].x <<" " << out[0].y << "\n";

    return 0;
}

Answer 1

你在问“intersectsb 是否”。

但是，您的第三个论点表明您想改为询问“intersection”：

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#include <boost/geometry.hpp>
#include <boost/geometry/geometries/register/point.hpp>
#include <boost/geometry/geometries/segment.hpp>
#include <iostream>

namespace bg = boost::geometry;
using namespace std;

struct cxy {
    double x = 0;
    double y = 0;
    cxy(double X, double Y) : x(X), y(Y) {}
    cxy() = default;
};

BOOST_GEOMETRY_REGISTER_POINT_2D(cxy, double, bg::cs::cartesian, x, y)
using segment_t = bg::model::segment<cxy>;
using points_t = bg::model::multi_point<cxy>;

int main() {
    cxy a{0, 0}, b{1, 1}, c{1, 0}, d{0, 1};
    std::vector<cxy> out;
    bg::intersection(segment_t{a, b}, segment_t{c, d}, out);

    // for output, use a multipoint model or register your vector as one
    points_t pts;
    bg::intersection(segment_t{a, b}, segment_t{c, d}, pts);
    std::cout << bg::wkt(pts) << "\n";
}

打印

MULTIPOINT((0.5 0.5))

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