c++ - boost geometry intersection give strange results -
i want use intersection function boost geometry line , polygon. expect intersection part of line lies inside polygon.
unfortunately boost geometry returns part of line lies outside of polygon. bug in boost geometry or wrong code?
#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; }
make sure input geometries satisfy pre-conditions documented.
you can use bg::correct fix issues (such proper ccw ordering of points in polygon, closing unclosed polygons etc.):
#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); } this prints
multilinestring((13.3769 53.6623,13.3857 53.6637,13.39 53.6646)) 
with input un-corrected have printed instead:
multilinestring((13.39 53.6646,13.3921 53.665,13.3972 53.6655,13.4072 53.6624)) 
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