CGAL users discussion list

["Max" <>]

>On Tue, 2008-02-12 at 00:09 +0800, Max wrote:
>> Hello Peter,
>> 
>> Sorry for my late response. But having more time studying the relevant 
>> stuff 
>> could get the discussion more effective.
>> 
>> >
>> >> My question is: How can I mannualy (with code) construct a 
>> >> (non-manifold) 
>> >> Nef_polyhedron given a set of vertices and facets in 3D?
>> >
>> >Actually, just as you tried. I hope that the number type makes the
>> >difference. We'll see.
>
>> I'm afraid I've not get all that you meant. :-)
>> 
>> I've had a look at the Shell_to_nef_3 visitor class, and it seems to be 
>> a kind of 'incremental builder' of nef_3 similar to that of Polyhedron_3. 
>> 
>
>You can use the incremental builder to construct a Polyhedron_3 and then
>convert it to a Nef_3. There is nothing like that for Nef_3.

One can convert a polyhedron to nef_3 by vonvert_to_polyhedron(). What I
need is to convert all of the facets to a polyhedron.

>> 3) In my understanding, the 'outter shell' (I mean by this name the shell 
>> that's only incident to the infinite volume) of a nef_3 is no different 
>> from those 'inner shells'. I attempted omitting the ++(N.volumes_begin()); 
>> statement to convert the 'outer shell' to a 'polyhedron' (here I means the 
>> data structure and file format similar to a polyhedron, not necissarily 
>> closed), but failed. Any hints is appriciated. (Both 'old' and 'new' impl
>> tested)
>
>Every volume is incident to one shell enclosing it (outer shell) and
>several inner shells bounding objects taken away from that volume. The
>volume always gives the outer shell first. Note that the unbounded
>volume does not have an outer shell. You cannot convert the inner shell
>of the infimaximal box into an off file. It does not have normal
>coordinates. Polyhedron_3 does not support such coordinates and it
>actually also does not make much sense.

It seems that my definition of 'outer shell' is different from yours.
Based on your (correct) definition, I want to get the inner shell of the 
unbounded
volume(including those shells only incident to volume 0) and convert to a 
polyhedron.
I do not need the information of the infimaximal box.
 
>I need time to browse through it, but the incremental builder does not
>work for Nef_3 objects---you can only build Polyhedron_3 objects with
>it.

I have attempted to adpat the original code to meet my needs (but failed).

>
>Peter
>-- 
>You are currently subscribed to cgal-discuss.
>To unsubscribe or access the archives, go to
>https://lists-sop.inria.fr/wws/info/cgal-discuss
>