在线串有效的情况下，使用boost段的comparative_distance失败

Question

我正在尝试计算点与线段之间的距离。但是以下代码在运行时突然终止（@comparable_distance）。

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

class Vertex {
public:
    Vertex(int px, int py):x(px), y(py){}
    int x;
    int y;
};

BOOST_GEOMETRY_REGISTER_POINT_2D(Vertex, double, cs::cartesian, x, y)

typedef Vertex* vertref;

typedef bg::model::segment<vertref> segment_type;

std::vector<segment_type> segments;

int main()
{
    segment_type l(new Vertex(1,2), new Vertex(2,2));
    Vertex p(4,5);
    double comp_dist = 0;
    comp_dist = bg::comparable_distance(p, l);

    cout<<comp_dist<<endl;

    return 0;
}

如果我将bg :: model :: segment替换为linestring;向其添加两个点，它可以正常工作，如下所示...

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

class Vertex {
public:
    Vertex(int px, int py):x(px), y(py){}
    int x;
    int y;
};

BOOST_GEOMETRY_REGISTER_POINT_2D(Vertex, double, cs::cartesian, x, y)

typedef Vertex* vertref;

typedef bg::model::linestring<vertref> segment_type;

std::vector<segment_type> segments;

int main()
{
    segment_type l;
    l.push_back(new Vertex(1,2));
    l.push_back(new Vertex(2,2));
    Vertex p(4,5);
    double comp_dist = 0;
    comp_dist = bg::comparable_distance(p, l);

    cout<<comp_dist<<endl;

    return 0;
}

有什么想法在使用段的第一个代码中我做错了吗？

谢谢！

调用堆栈...

#0 0x40486f boost::geometry::traits::access<Vertex, 0u, void>::set(p=..., value=@0x63fde8: 1) (C:\Projects\test\main.cpp:17)
#1 0x403e14 boost::geometry::core_dispatch::access<boost::geometry::point_tag, Vertex, double, 0u, boost::integral_constant<bool, true> >::set(p=0x77b12580, value=@0x63fde8: 1) (C:/boost_1_68_0/boost/geometry/core/access.hpp:187)
#2 0x404182 boost::geometry::set<0u, Vertex*>(geometry=@0x63fe34: 0x77b12580, value=@0x63fde8: 1, dummy=0x0) (C:/boost_1_68_0/boost/geometry/core/access.hpp:321)
#3 0x40469a boost::geometry::detail::assign::assign_point_from_index<boost::geometry::model::segment<Vertex*>, Vertex*, 0u, 0u, 2u>::apply(geometry=..., point=@0x63fe34: 0x77b12580) (C:/boost_1_68_0/boost/geometry/algorithms/detail/assign_values.hpp:195)
#4 0x4045de boost::geometry::detail::assign_point_from_index<0u, Vertex*, boost::geometry::model::segment<Vertex*> >(geometry=..., point=@0x63fe34: 0x77b12580) (C:/boost_1_68_0/boost/geometry/algorithms/detail/assign_indexed_point.hpp:80)
#5 0x4049fc boost::geometry::dispatch::distance<Vertex, boost::geometry::model::segment<Vertex*>, boost::geometry::strategy::distance::projected_point<void, boost::geometry::strategy::distance::comparable::pythagoras<void> >, boost::geometry::point_tag, boost::geometry::segment_tag, boost::geometry::strategy_tag_distance_point_segment, false>::apply(point=..., segment=..., strategy=...) (C:/boost_1_68_0/boost/geometry/algorithms/detail/distance/point_to_geometry.hpp:419)
#6 0x403f9b boost::geometry::resolve_strategy::comparable_distance::apply<Vertex, boost::geometry::model::segment<Vertex*> >(geometry1=..., geometry2=...) (C:/boost_1_68_0/boost/geometry/algorithms/detail/comparable_distance/interface.hpp:83)
#7 0x403f38 boost::geometry::resolve_variant::comparable_distance<Vertex, boost::geometry::model::segment<Vertex*> >::apply<boost::geometry::default_strategy>(geometry1=..., geometry2=..., strategy=...) (C:/boost_1_68_0/boost/geometry/algorithms/detail/comparable_distance/interface.hpp:106)
#8 0x403ff5 boost::geometry::comparable_distance<Vertex, boost::geometry::model::segment<Vertex*>, boost::geometry::default_strategy>(geometry1=..., geometry2=..., strategy=...) (C:/boost_1_68_0/boost/geometry/algorithms/detail/comparable_distance/interface.hpp:328)
#9 0x403fc9 boost::geometry::comparable_distance<Vertex, boost::geometry::model::segment<Vertex*> >(geometry1=..., geometry2=...) (C:/boost_1_68_0/boost/geometry/algorithms/detail/comparable_distance/interface.hpp:356)
#10 0x401518    main() (C:\Projects\test\main.cpp:30)

Answer 1

Segment Concept由model::segment建模，该Point采用模拟Live On Coliru的模板参数。

现在您使用了：

typedef Vertex *vertref;

typedef bg::model::segment<vertref> segment_type;

请注意，vertref实际上不是为Point概念建模的对象。因此，相比之下，请考虑：

#include <boost/geometry.hpp>
#include <boost/geometry/geometries/register/point.hpp>
#include <iostream>
namespace bg = boost::geometry;

struct Vertex {
    double x;
    double y;
};

BOOST_GEOMETRY_REGISTER_POINT_2D(Vertex, double, bg::cs::cartesian, x, y)

typedef bg::model::segment<Vertex> segment_type;

int main() {
    segment_type l({1, 2}, {2, 2});
    Vertex p {4, 5};

    auto comp_dist = bg::comparable_distance(p, l);

    std::cout << comp_dist << "\n";
}

打印：

13

实际上13是实际距离的平方：Live On Coliru

奖金

为回应评论，是的，甚至还存在针对参考点（来自其他几何）的线段的现成模型。 referring_segment<>的使用方法如下：

#include <boost/geometry.hpp>
#include <boost/geometry/geometries/register/point.hpp>
#include <iostream>
namespace bg = boost::geometry;

struct Vertex {
    double x;
    double y;
};

BOOST_GEOMETRY_REGISTER_POINT_2D(Vertex, double, bg::cs::cartesian, x, y)

typedef bg::model::referring_segment<Vertex> segment_type;

int main() {
    Vertex A{1,2},
           B{2,2};
    segment_type l(A, B);
    Vertex p {4, 5};

    std::cout << bg::distance(p, l) << "\n";

    bg::multiply_value(A, -1);
    bg::multiply_value(B, -1);
    std::cout << bg::distance(p, l) << "\n";
}

打印前后突变的距离：

3.60555
8.60233

这又符合您的期望：Why should C++ programmers minimize use of 'new'?

注意：

1. 在C ++中使用new几乎总是一个错误。此错误最常见的是来自Java或C＃（{{3}}）等垃圾收集语言的初学者
2. 类型不一致（成员x，y是int个）