CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

On 07/17/2012 02:50 AM, 马良 wrote:
> Hello Sebastien Loriot,
> Thank you replay.
> Yes, I test the example of AABB tree demo. There is no problem to 
> caculate intersections between a plane and polyhedron.
> But, the results of intersections are many Segment object. I debug those 
> segments, and find that those intersetion segments is no end to end 
I guess because you are using a kernel with inexact constructions.
Try with Exact_predicates_inexact_constructions_kernel for example.

http://www.cgal.org/FAQ.html#inexact_NT

Sebastien.

> Sequentially.
> I want to find loops (segment attach together sequentially).
> 
> My question:How to constitute "Loops" using those segments??
> 
> 
> 2012/7/13 Sebastien Loriot (GeometryFactory) 
> <
>  
> <mailto:>>
> 
>     If you run the AABB_tree demo, you can open an off file (simple to
>     create from stl), then
>     run Algorithms ->cut plane -> intersection.
> 
>     You can extract the code from the demo (file Scene.cpp function
>     cut_segment_plane).
> 
>     The principal is simple: you create an aabb_tree using the facets of the
>     mesh, and you
>     create all intersections with you plane.
> 
>     See:
>     
> http://www.cgal.org/Manual/latest/doc_html/cgal_manual/AABB_tree_ref/Class_AABB_tree.html
> 
>     Sebastien.
> 
>     On 07/13/2012 03:29 AM, 马良 wrote:
>      > Hi
>      > I read a STL-file (a kind of file using in RapidPrototyping, a
>     triangle
>      > in STL is composed of 3-Point and normal). And I create a Polyhedron
>      > like a following.
>      > Polyhedron P;
>      > P.make_triangle(V1,V2,V3);
>      > P.make_triangle(V4,V5,V6);
>      > ....
>      > //Then, I create AABB tree, as follows:
>      > Facet_tree tree(P.facets_begin(),P.facets_end());
>      > //Next, I create a plane and caculate intersections between plane and
>      > polyhedron
>      > Vector nor(0,0,1);
>      > Point pnt(0,0,0.5);
>      > Plane plane(pnt,nor);
>      > tree.all_intersections(plane,std::back_inserter(Intersetions));
>      > //Here, I get intersetions (Points: (X,Y,Z))
>      > for( it = Intersetions.begin();it !=Intersections.end();it++)
>      > {
>      > if(CGAL::assign(segment,object) m_segment.push_back(segment);
>      > }
>      > // But, I get a lot of segments. And Here I want get contours (a
>     contour
>      > is composed of segments in order).
>      > My question is How to constitute contours using segments. Whether
>     or not
>      > I must sort those segments by myself? Here is a algorithm in CGAL?
>      > Thanks!
>      >
>      > --
>      > 马良 Mr.MaLiang
>      > State Key Laboratory of Solidification Processing
>      > Northwestern Polytechnical University
>      > Xi'an 710072, Shanxi
>      > P. R. China
>      > Tel/Fax:+86(29)88460520
>      > Mobile:+86(0)15829297776
>      > Email: 
> 
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>      > QQ number:394646034
>      >
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> 
> -- 
> 马良 Mr.MaLiang
> State Key Laboratory of Solidification Processing
> Northwestern Polytechnical University
> Xi'an 710072, Shanxi
> P. R. China
> Tel/Fax:+86(29)88460520
> Mobile:+86(0)15829297776
> Email: 
> 
>  
> <mailto:>
> QQ number:394646034
>