
Geometry : 
Subject: Re: [geometry] self intersection doesn't find collinear intersection types
From: Adam Wulkiewicz (adam.wulkiewicz_at_[hidden])
Date: 20160511 06:19:31
Hi Sergei,
Sergei Benkovich wrote:
> Hey,
> i have an issue where i find self intersections in a polygon.but it
> doesn't seem to find the method_collinear type.
>
> this is the piece of code:
>
>
> namespace bg = boost::geometry;
> using namespace std;
> typedef bg::model::d2::point_xy<double> point_2d;
> typedef
> bg::model::polygon<boost::geometry::model::d2::point_xy<double> > Polygon;
> Polygon poly;
> poly.outer().push_back(point_2d(0, 10));
> poly.outer().push_back(point_2d(10, 0));
>
Have in mind that this polygon is invalid (too small number of points)
so it may even be ignored (I don't remember).
But of course if you had a valid polygon like:
Polygon poly{ { {0, 0},{0, 10}, {10, 10}, {10, 0}, {0, 0} } };
There would be no self intersections returned because the polygon is not
selfintersecting.
However if you had a (invalid) Polygons like this:
Polygon poly{ { {0, 0},{0, 10}, {10, 10}, {10, 0}, {0, 0},{ 0, 10 },{
10, 10 },{ 10, 0 },{ 0, 0 } } };
Polygon poly{ { {0, 0},{0, 10}, {10, 10}, {10, 0}, { 10, 10 },{ 0, 10
},{ 0, 0 } } };
you'd get collinear and blocking selfintersection turns respectively.
Regards,
Adam
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