CGAL users discussion list

["Jens K. Becker" <>]

Hi alex,

I thought about alpha shapes, but the it is not garanteed that the
spacing of vertices is such that I can "just" cut away parts and end up
with what I need. It has to be done automatically, no user interaction
is possible. I will have a look at the link you gave, I hope that will
do the trick..

Greetings,

Jens

On Sat, 2009-06-06 at 19:22 +0530, alex wrote:
>  
> Hi
>  
> I think you need Alpha shape that doing surface reconstruction job for
> you that will found in Alpha package. or You can try this one also but
> you have to do some code changes it is in java
>  
> http://www.loria.fr/~pougetma/software/reconstruction/reconstruction.html
>  
>  
> alex
>  
>  
>         ----- Original Message ----- 
>         From: Bo Zhou 
>         To: 
> 
>  
>         Sent: Saturday, June 06, 2009 5:25 PM
>         Subject: Re: [cgal-discuss] 3D Triangulation / surface
>         reconstruction
>         
>         
>         Jens K. Becker wrote: 
>         > Hi all,
>         > 
>         > I am puzzling over this problem for quite some time now and just 
> cant
>         > find a solution... I have a set of polyhedra that share facets and
>         > vertices. Obviously, each facet can only belong to two polyhedra 
> while a
>         > vertex might belong to much more. If I want to delete a facet (or 
> a
>         > vertex) or add a facet (or a vertex) to one polyhedron, I have to 
> add
>         > the same to other polyhedra too. The most convenient would be to
>         > construct a (Delaunay) triangulation of the part of the polyhedra 
> where
>         > things are going to happen, do whatever has to be done and 
> reconstruct
>         > the polyhedra from that triangulation. But how? The problem is the
>         > reconstruction because I cannot think of any way how to decide 
> which
>         > facet of the triangulation belongs to which polyhedron. Is there 
> an easy
>         > way to do this? Or a hard way?
>         > 
>         > The triangulation would typically consist of 20-30 vertices only, 
> I can
>         > store which vertex belongs to which polyhedron in the vertices 
> and/or I
>         > could store which facet belongs to which polyhedron (before
>         > inserting/deleting things from the triangulation) but I did not 
> figure
>         > out a way how to reconstruct it from this information. 
>         > 
>         > I tried to have a look at the example in CGAL3.4 that does 
> remeshing of
>         > a polyhedron, but did not really understand what is happening 
> there (and
>         > could not get it to compile neither, but that's another story). 
>         > 
>         > If anybody has any ideas, I would be very happy. He/she will be 
> invited
>         > for beers (wine, water you decide...) should we ever meet!
>         > 
>         > Thanks for any help,
>         > 
>         > Jens Becker
>         > 
>         >   
>         Hello,
>         I think maybe the meshes you need to deal with are like this
>         one (from SIGGRAPH 2000 Course Notes Subdivision for Modeling
>         and Animation) if I have not misunderstood the situation you
>         illustrated.
>         
>         To mark the facets to which mesh they belongs, maybe you can
>         redefine some basic structure like the demo
>         "examples/Polyhedron/polyhedron_prog_color.cpp" or in PDF
>         manual page 1523, it redefined the half-edge structure to add
>         a color component.
>         
>         -- 
>         /**
>         * Bo Zhou
>         * Blog : http://jedimaster.cnblogs.com
>         * Mobile : +86 13451813691
>         */
-- 
Dr. J.K. Becker
University of Tuebingen - Institute for Geoscience
Sigwartst. 10 - 72076 Tuebingen (Germany)
Tel.: ++49 7071 29 73139   Fax: +49 7071 5059
Web: http://www.jkbecker.de