c++ - boost 几何交集给出奇怪的结果

Question

我想使用 boost geometry 中的 intersection 函数与一条线和一个多边形。我希望交点是位于多边形内部的线的一部分。

不幸的是，boost geometry 返回了位于多边形之外的线部分。这是 boost geometry 中的错误还是我的代码有问题？

#include <boost/geometry/core/cs.hpp>
#include <boost/geometry/geometries/point.hpp>
#include <boost/geometry/geometries/ring.hpp>
#include <boost/geometry/geometries/box.hpp>
#include <boost/geometry/geometries/segment.hpp>
#include <boost/geometry/geometries/linestring.hpp>
#include <boost/geometry/multi/geometries/multi_point.hpp>
#include <boost/geometry/multi/geometries/multi_linestring.hpp>
#include <boost/geometry/geometry.hpp>
#include <boost/geometry/geometries/geometries.hpp>
#include <boost/geometry/algorithms/intersection.hpp>

namespace bg = boost::geometry;

using value_type = double ;
using cs_type = bg::cs::cartesian;
using point_type = bg::model::point< value_type , 2 , cs_type >;
using polygon_type = bg::model::ring< point_type > ;
using line_string_type = bg::model::linestring< point_type >;
using multi_line_type = bg::model::multi_linestring< line_string_type >;

int main( int argc , char *argv[] )
{
    line_string_type line;
    line.push_back( point_type { 13.37688020921095 , 53.66231710654281 } );
    line.push_back( point_type { 13.3857295713429 , 53.6636835518369 } );
    line.push_back( point_type { 13.39213495232734 , 53.66501934623722 } );
    line.push_back( point_type { 13.39719615524716 , 53.66546436809296 } );
    line.push_back( point_type { 13.40724694386097 , 53.66240690770171 } );

    polygon_type polygon;
    polygon.push_back( point_type { 13.35 , 53.64 } );
    polygon.push_back( point_type { 13.39 , 53.64 } );
    polygon.push_back( point_type { 13.39 , 53.68 } );
    polygon.push_back( point_type { 13.35 , 53.68 } );
    polygon.push_back( point_type { 13.35 , 53.64 } );

    multi_line_type intersection;
    bg::intersection( line , polygon , intersection );

    return 0;
}

Answer 1

确保您的输入几何满足记录的先决条件。

您可以使用 bg::correct 来解决大多数问题(例如多边形中点的正确 CCW 排序、闭合未闭合的多边形等):

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#include <boost/geometry/core/cs.hpp>
#include <boost/geometry/geometries/point.hpp>
#include <boost/geometry/geometries/ring.hpp>
#include <boost/geometry/geometries/box.hpp>
#include <boost/geometry/geometries/segment.hpp>
#include <boost/geometry/geometries/linestring.hpp>
#include <boost/geometry/multi/geometries/multi_point.hpp>
#include <boost/geometry/multi/geometries/multi_linestring.hpp>
#include <boost/geometry/geometry.hpp>
#include <boost/geometry/geometries/geometries.hpp>
#include <boost/geometry/algorithms/intersection.hpp>

namespace bg = boost::geometry;

using value_type       = double;
using cs_type          = bg::cs::cartesian;
using point_type       = bg::model::point<value_type, 2, cs_type>;
using polygon_type     = bg::model::ring<point_type>;
using line_string_type = bg::model::linestring<point_type>;
using multi_line_type  = bg::model::multi_linestring<line_string_type>;

int main()
{
    line_string_type line;
    line.push_back(point_type{13.37688020921095, 53.66231710654281});
    line.push_back(point_type{13.3857295713429,  53.6636835518369});
    line.push_back(point_type{13.39213495232734, 53.66501934623722});
    line.push_back(point_type{13.39719615524716, 53.66546436809296});
    line.push_back(point_type{13.40724694386097, 53.66240690770171});
    bg::correct(line);

    polygon_type polygon;
    polygon.push_back(point_type{13.35, 53.64});
    polygon.push_back(point_type{13.39, 53.64});
    polygon.push_back(point_type{13.39, 53.68});
    polygon.push_back(point_type{13.35, 53.68});
    polygon.push_back(point_type{13.35, 53.64});
    bg::correct(polygon);

    multi_line_type intersection;
    bg::intersection(line, polygon, intersection);

    std::cout << bg::wkt(intersection);
}

这打印

MULTILINESTRING((13.3769 53.6623,13.3857 53.6637,13.39 53.6646))

如果输入未被正确编辑，它会打印如下:

MULTILINESTRING((13.39 53.6646,13.3921 53.665,13.3972 53.6655,13.4072 53.6624))