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Re: [cgal-discuss][Nef_polyhedron] How to convertaNef_polyhedron_3 into a Nef_polyhedron_2 if meaningful


Chronological Thread 
  • From: "Max" <>
  • To: "" <>
  • Subject: Re: [cgal-discuss][Nef_polyhedron] How to convertaNef_polyhedron_3 into a Nef_polyhedron_2 if meaningful
  • Date: Fri, 11 Jan 2008 08:49:57 +0800
  • Disposition-notification-to: "Max" <>
  • Organization: LoadCom

Hello Peter

Thank you so much for your continuous help.

B/Rgds
Max

----- Original Message ----
From: Peter Hachenberger
To:

Sent: 2008-01-10 22:55:20
Subject: Re: Re: [cgal-discuss][Nef_polyhedron] How to
convertaNef_polyhedron_3 into a Nef_polyhedron_2 if meaningful

>
I already gave you the answer:

store the points of the Nef_3 and then pass those points to the
constructor of the Nef_2

That should also work with Polygon/Polygon_with_hole in some way.

Peter

On Wed, 2008-01-09 at 10:01 +0800, LoadCom wrote:
> Hello Peter,
>
> Thanks for your quick response. It's very helpful indeed.
>
> It's not a surprise to know that the designer of CGAL has never thought
> of such a *strange* conversion. Perhaps it's too wild. :-)
>
> From your reply, it seems that it's still possible (I mean not so hard)
> to write some code to get such a conversion.
>
> At the present time, efficiency is probably not a main problem for me. The
> result I desired is somthing that similar in topology to a Nef_2, or
> perferrably,
> in terms of a Polygon_with_hole data structure. With that, I can get to
> calculte some geometric properties of this polygon, including center of
> area,
> moment of inertia, and so on.
>
> If possible, could you please give me some more detailed instruction with
> which I could accomplish that needs?
>
> I really appreciat the help you've given me.
>
> B/Rgds
> Max
>
> ----- Original Message ----
> From: Peter Hachenberger
> To:
>
> Sent: 2008-01-08 18:38:41
> Subject: Re: [cgal-discuss][Nef_polyhedron] How to convert
> aNef_polyhedron_3 into a Nef_polyhedron_2 if meaningful
>
> >
> Hi Max,
>
> we never really thought about this conversion. So, we don't have it. An
> easy thing to do is just to store the points of the Nef_3 and then pass
> those points to the constructor of the Nef_2. I guess that any
> conversion tool I could write would not be more efficient than that. The
> main disadvantage to a real conversion is, that you loose the marks. The
> constructor does not allow you to choose for every edge whether it is
> selected or not. Does that help you?
>
> Peter
>
> On Mon, 2008-01-07 at 15:38 +0800, LoadCom wrote:
> > Hello,
> >
> > Suppose I have a closed Nef_polyhedron_3 N, and I construct a plane with
> > Nef_polyhedron_3 in this manner
> >
> > Nef_polyhedron_3 N; // closed
> >
> > // now constructing a plane Nef
> > Plane_3 pl(1, 1, 1, 0);
> > Nef_polyhedron_3 N_plane(Nef_polyhedron_3(pl) * !Nef_polyhedron_3(pl,
> > Nef_polyhedron::EXCLUDED));
> >
> > // Now I intersect these 2 Nef:
> >
> > Nef_polyhedron_3 N_res = N * N_plane;
> >
> > Now N_res is actually a Nef_polyhedron_2, but is there a way to convert
> > it into a Nef_polyhedron_2
> > and then explore it accordingly?
> >
> > Thanks in advance.
> > Max
> >
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