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[马良 <>]

Hello,

        I get many segments by intersecting a plane and polyhedron. But I find those segments(start point:Point(x1,y1), end point: Point(x2,y2)) are not end to end. I want get a loop (That means adjacent two segments must share a same Vertex. That is to say previour segment's end point is current segment's start point, and current segment's end point is next segment's start point, And so. )

        How can I arrangement those segments?

        I think, firstly, I get a vertex of segment, then find a same vertex in remaining segments. Then find next.

        there have easy way to do this in CGAL?

 

        My source:

//1. 

 typedef CGAL::Polyhedron_3<Kernel> Polyhedron;
 //Facet
 typedef CGAL::AABB_polyhedron_triangle_primitive<Kernel,Polyhedron> Facet_Primitive;
 typedef CGAL::AABB_traits<Kernel,Facet_Primitive>     Facet_Traits;
 typedef CGAL::AABB_tree<Facet_Traits>        Facet_tree;
 //
 typedef Facet_tree::Object_and_primitive_id Object_and_primitive_id;
 //
 typedef Kernel::FT FT;
 typedef Kernel::Point_3 Point;
 typedef Kernel::Plane_3 Plane;
 typedef Kernel::Vector_3 Vector;
 typedef Kernel::Segment_3 Segment;
 //2. 

 Point V1(0.0,0.0,0.0);
 Point V2(1.0,0.0,0.0);
 Point V3(1.0,1.0,0.0);
 Point V4(0.0,1.0,0.0);
 Point V5(0.0,0.0,1.0);
 Point V6(1.0,0.0,1.0);
 Point V7(1.0,1.0,1.0);
 Point V8(0.0,1.0,1.0);
 //3. 

 Polyhedron P;
 P.make_triangle(V1,V6,V5);
 P.make_triangle(V1,V2,V6);

 P.make_triangle(V2,V7,V6);
 P.make_triangle(V2,V3,V7);

 P.make_triangle(V3,V8,V7);
 P.make_triangle(V3,V4,V8);

 P.make_triangle(V4,V5,V8);
 P.make_triangle(V4,V1,V5);

 P.make_triangle(V5,V6,V7);
 P.make_triangle(V5,V7,V8);

 P.make_triangle(V1,V3,V2);
 P.make_triangle(V1,V4,V3);
//4. 

 Vector nor((FT)0.0,(FT)0.0,(FT)1.0);
 Point pnt((FT)0.0,(FT)0.0,0.5);
 Plane plane(pnt,nor);

//5.1. AABB tree
 Facet_tree tree(P.facets_begin(),P.facets_end());
 //5.2. get intersections a plane and polyhedron

 std::list<Object_and_primitive_id> Intersections;
 tree.all_intersections(plane,std::back_inserter(Intersections));

 std::list<Object_and_primitive_id>::iterator it;
 std::list<Segment> m_segment;
 for(it = Intersections.begin();it!=Intersections.end();it++)
 {
  Object_and_primitive_id op = *it;
  CGAL::Object object = op.first;
  Segment segment;
  if(CGAL::assign(segment,object)) m_segment.push_back(segment);
 }

 

Note:

    Here, I get intersection segments. But those segment is not link Sequentially.

    How to connect those segments into loop???

 

Thanks

 

Ma Liang
--

马良  Mr.MaLiang
State Key Laboratory of Solidification Processing
Northwestern Polytechnical University
Xi'an 710072, Shanxi
P. R. China
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