Schnittpunkt von boost :: geometry :: model :: linestring mit boost :: geometry :: model :: polygon

Question

Ich versuche den Teil einer Linienfolge innerhalb eines Polygons zu finden. Ich habe versucht, die intersection Funktion, aber es scheint nur die tatsächlichen Schnittpunkte und nicht den Teil der Linienfolge, die das Polygon überlappt. Gibt es eine Möglichkeit, dieses Objekt zu bekommen?

Hier ist eine Demo-Situation:

#include <iostream> 
#include <fstream> 

#include <boost/geometry.hpp> 
#include <boost/geometry/geometries/point_xy.hpp> 
#include <boost/geometry/geometries/polygon.hpp> 
#include <boost/geometry/io/svg/svg_mapper.hpp> 
#include <boost/geometry/geometries/linestring.hpp> 

using point_type = boost::geometry::model::d2::point_xy<double>; 
using polygon_type = boost::geometry::model::polygon<point_type>; 
using linestring_type = boost::geometry::model::linestring<point_type>; 

int main() 
{ 
    polygon_type polygon; 

    polygon.outer().push_back(point_type{10,10}); 
    polygon.outer().push_back(point_type{12,10}); 
    polygon.outer().push_back(point_type{12,12}); 
    polygon.outer().push_back(point_type{10,12}); 
    polygon.outer().push_back(point_type{10,10}); 

    linestring_type linestring; 
    linestring.push_back(point_type{11,9}); 
    linestring.push_back(point_type{11,11}); 
    linestring.push_back(point_type{13,11}); 

    // Expected intersections at (11, 10) and (12, 11) 

    std::ofstream svg("both.svg"); 

    linestring_type output; 
    boost::geometry::intersection(polygon, linestring, output); 

    for(auto iter = output.begin(); iter != output.end(); ++iter) { 
     std::cout << boost::geometry::get<0>(*iter) << " " << boost::geometry::get<1>(*iter) << std::endl; 
    } 
// The output is: 
// 11 10 
// 12 11 

// But I want it to be: 
// 11 10 
// 11 11 
// 12 11 
    return 0; 
} 

Answer 1

Es scheint, dass Sie eine multi_linestring als Ausgabetyp verwenden müssen:

#include <iostream> 

#include <boost/geometry.hpp> 
#include <boost/geometry/geometries/point_xy.hpp> 
#include <boost/geometry/geometries/polygon.hpp> 
#include <boost/geometry/geometries/linestring.hpp> 
#include <boost/geometry/multi/geometries/multi_linestring.hpp> 

using point_type = boost::geometry::model::d2::point_xy<double>; 
using polygon_type = boost::geometry::model::polygon<point_type>; 
using linestring_type = boost::geometry::model::linestring<point_type>; 
using multi_linestring_type = boost::geometry::model::multi_linestring<linestring_type>; 

int main() 
{ 
    polygon_type polygon; 

    polygon.outer().push_back(point_type{10,10}); 
    polygon.outer().push_back(point_type{10,12}); 
    polygon.outer().push_back(point_type{12,12}); 
    polygon.outer().push_back(point_type{12,10}); 
    polygon.outer().push_back(point_type{10,10}); 

    linestring_type linestring; 
    linestring.push_back(point_type{11,9}); 
    linestring.push_back(point_type{11,11}); 
    linestring.push_back(point_type{13,11}); 

    // Expected intersections at (11, 10) and (12, 11) 

    multi_linestring_type intersection; 
    boost::geometry::intersection(polygon, linestring, intersection); 

    for(auto intersectionIter = intersection.begin(); intersectionIter != intersection.end(); ++intersectionIter) { 
     linestring_type intersectionPiece = *intersectionIter; 
     std::cout << "Piece:" << std::endl; 
     for(auto intersectionPieceIter = intersectionPiece.begin(); intersectionPieceIter != intersectionPiece.end(); ++intersectionPieceIter) { 
      std::cout << boost::geometry::get<0>(*intersectionPieceIter) << " " << boost::geometry::get<1>(*intersectionPieceIter) << std::endl; 
     } 

    } 

    return 0; 
}