Boost几何相交无法正确输出 [英] Boost geometry intersection does not output correctly

问题描述

从以下代码中，我计算出两个多边形的交点.我希望如果不是多边形，则输出可以为NULL.但是输出为((((240，52.9999)，(240，53)，(240，53)，(240，52.9999)))).这不是多边形.有什么方法可以检查输出是否真的是多边形?

  #include< iostream>#include< deque>#include< vector>#include< boost/geometry.hpp>#include< boost/geometry/geometries/point_xy.hpp>#include< boost/geometry/geometries/polygon.hpp>#include< boost/geometry/io/wkt/wkt.hpp>#include< boost/geometry/algorithms/append.hpp>#include< algorithm>//反向，唯一#include< iostream>#include< string>int main(){typedef boost :: geometry :: model :: d2 :: point_xy< double，boost :: geometry :: cs :: cartesian>point_2d;typedef boost :: geometry :: model :: polygon< point_2d>多边形_2d;多边形_2d绿色；boost :: geometry :: append(green，point_2d(286.188，90.9575));boost :: geometry :: append(green，point_2d(274.902，56.2215));boost :: geometry :: append(green，point_2d(274.238，55.7393));boost :: geometry :: append(green，point_2d(246.908，51.9765));boost :: geometry :: append(green，point_2d(194.477，59.7441));boost :: geometry :: append(green，point_2d(159.213，101.141));boost :: geometry :: append(green，point_2d(203.576，149.537));boost :: geometry :: append(green，point_2d(286.188，90.9575));多边形_2d蓝色；boost :: geometry :: append(blue，point_2d(240，53));boost :: geometry :: append(blue，point_2d(240，-53));boost :: geometry :: append(blue，point_2d(-60，-53));boost :: geometry :: append(blue，point_2d(-60，53));boost :: geometry :: append(blue，point_2d(240，53));boost :: geometry :: correct(绿色);boost :: geometry :: correct(blue);std :: vector< polygon_2d>输出;boost :: geometry :: intersection(绿色，蓝色，输出)；std :: cout<<绿色&&蓝色:"<<std :: endl;如果(output.size()){std :: cout<< boost :: geometry :: dsv(output [0])<< std :: endl;std :: cout<< boost :: geometry :: area(output [0])<< std :: endl;}返回0;} 

解决方案

您可以清除无效的几何图形:

  output.erase(std :: remove_copy_if(output.begin()，output.end()，output.begin()，[](polygon_2d const& g){return boost :: geometry :: is_valid(g);})，output.end()); 

现在，结果将为空.

查看 或增强多精度，例如:

  typedef boost :: multiprecision :: number< boost :: multiprecision :: cpp_bin_float< 1024 * 128>oopmh;//这是一个很大的魅力typedef boost :: geometry :: model :: d2 :: point_xy< oopmh，boost :: geometry :: cs :: cartesian>point_2d; 

您会看到我们得到了

 绿色&&蓝色的:((((2.4e + 06，530000)，(-600000，530000)，(-600000，-530000)，(2.4e + 06，-530000)，(2.4e + 06，530000)))nan 

因此，看起来非常像我们只是获得了一个奇异点.如果您不希望这样做，那么也许您应该只定义sorts的"epsilon"值，即停止考虑重叠和重叠的阈值.

From the following code I calculate the intersection of two polygons. I hope the output can be NULL if it is not polygon. However the output is (((240, 52.9999), (240, 53), (240, 53), (240, 52.9999))). This is not a polygon. Is there any way to check whether the output is really a polygon??

#include <iostream>
#include <deque>
#include <vector>
#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#include <boost/geometry/geometries/polygon.hpp>
#include <boost/geometry/io/wkt/wkt.hpp>
#include <boost/geometry/algorithms/append.hpp>

#include <algorithm> // for reverse, unique
#include <iostream>
#include <string>


int main()
{
   typedef boost::geometry::model::d2::point_xy<double,    boost::geometry::cs::cartesian> point_2d;
   typedef boost::geometry::model::polygon<point_2d> polygon_2d;

    polygon_2d green;
    boost::geometry::append(green, point_2d(286.188, 90.9575));
    boost::geometry::append(green, point_2d(274.902, 56.2215));
    boost::geometry::append(green, point_2d(274.238, 55.7393));
    boost::geometry::append(green, point_2d(246.908, 51.9765));
    boost::geometry::append(green, point_2d(194.477, 59.7441));
    boost::geometry::append(green, point_2d(159.213, 101.141));
    boost::geometry::append(green, point_2d(203.576, 149.537));
    boost::geometry::append(green, point_2d(286.188, 90.9575));

    polygon_2d blue;
    boost::geometry::append(blue, point_2d(240, 53));
    boost::geometry::append(blue, point_2d(240, -53));
    boost::geometry::append(blue, point_2d(-60, -53));
    boost::geometry::append(blue, point_2d(-60, 53));
    boost::geometry::append(blue, point_2d(240, 53));

    boost::geometry::correct(green);
    boost::geometry::correct(blue);

    std::vector<polygon_2d> output;
    boost::geometry::intersection(green, blue, output);

    std::cout << "green && blue:" << std::endl;
    if(output.size())
    {
       std::cout<<boost::geometry::dsv(output[0])<<std::endl;
       std::cout<<boost::geometry::area(output[0])<<std::endl;
    }

    return 0;
}

解决方案

You can weed out the invalid geometries:

output.erase(
        std::remove_copy_if(output.begin(), output.end(), output.begin(), [](polygon_2d const&g) { return boost::geometry::is_valid(g); }),
        output.end());

Now, the result will be empty as expected.

See it Live On Coliru

---

It's interesting to me how "invalid" geometries would result in the first place. As you were probably aware that your polygons are very well chosen:

Let's zoom in a little:

Now, you're likely looking at some floating point accuracy issues, as the same experiment with long long points or boost multiprecision, e.g.:

typedef boost::multiprecision::number<boost::multiprecision::cpp_bin_float<1024*128>> oopmh; // that's a lotta oomph
typedef boost::geometry::model::d2::point_xy<oopmh, boost::geometry::cs::cartesian> point_2d;

You will see that we get

green && blue:
(((2.4e+06, 530000), (-600000, 530000), (-600000, -530000), (2.4e+06, -530000), (2.4e+06, 530000)))
nan

So it looks very much like we just get a singular point of area. If you don't want this, then maybe you should just define an "epsilon" value of sorts, a threshold at which you stop considering an overlap an overlap.

这篇关于Boost几何相交无法正确输出的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！