Question

I have a set of polygons and I want to test intersection between it and a segment.
I checked the manual but I cannot find a matching function.
The intersection between points, lines, segments, triangles, planes do exist.
And the intersection between polygons are also there.
My question is:

1. Is there such a function?
2. If not, does it mean I need to break down the polygons into segments and do intersection among these segments? (The reason that I am reluctant to do this is, I thought CGAL might in fact use this way to do intersections between polygons. How come there is no such a function for intersecting a line and a polygon?) Or is there any other better way to do it?

Answer 1

The easiest method is to create a Polygon_set_2 object which may contain several polygons. To test an intersection of an external polygon with this set you simply apply the do_intersect method.

For example:

typedef CGAL::Polygon_set_2<Kernel, std::vector<Kernel::Point_2>> Polygon_set_2;
Polygon_set_2 ps;
Polygon_2     poly;
Polygon_2     line; // line is a polygon defined by 2 points

ps.insert(poly);
bool intersect = ps.do_intersect(line);

More on polygon_set_2:

• http://www.cgal.org/Manual/3.2/doc_html/cgal_manual/Boolean_set_operations_2_ref/Class_General_polygon_set_2.html
• http://www.cgal.org/Manual/3.2/doc_html/cgal_manual/Boolean_set_operations_2_ref/Class_Polygon_set_2.html

I hope it’s clear,
Kiril