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From: Huseyin Akcan (huseyinakcan_at_[hidden])
Date: 2007-04-14 12:51:23

Dear John,

Thanks for the pointers and papers, I'll check them for sure.
A standard point concept is not in the plan (at least for the summer project).
As geometric objects are widely used, the expectations also varies a
lot, so we had
to limit ourselves in terms of features.



On 4/14/07, John Femiani <JOHN.FEMIANI_at_[hidden]> wrote:
> > Dear Fernando,
> >
> > The implementation will be based on half-edge scheme. However by using
> > Boost.Intrusive adapters, it would be possible for our algorithms to
> use
> > the BGL representations as well.
> >
> > When talking about the 2D we mainly talk about the combinatorial
> > information, so I'll say its the topology (if this is what you mean by
> > topology).
> >
> > Thank you (and others), its really great to get this much interest
> > from the community.
> >
> > huseyin
> Hey if you are interested, there is a library I explored before
> ( and of course I think CGAL has a half-edge (or maybe
> double-edge) mesh. I think that it would be good if you can at least
> model the BGL Concepts, so that the BGL algorithms can be applied to the
> mesh.
> There is a much more generic concept than half-edge (HE) meshes called a
> 'lath' mesh
> (
> Unfortunately I only read about this (and several other papers) after
> learning the hard way that a HE mesh does not suit every purpose. This,
> or something like it, is important to me because in many scenarios a
> mesh is not always manifold all the time, especially if you wish to
> maintain the connectivity as you operate on it by adding and removing
> faces. A HE mesh can not adequately represent a non manifold mesh, such
> as would result when you deleted two non-adjacent triangles from a
> vertex and filled-in the gap between them with a single polygon for
> example. In fact that type of operation can be EXTREMELY tricky if I
> remember because the corners at a vertex on more than one hole have no
> ordering between them, and you have to carefully consider legitimate
> ways to shuffle the wedges (connected sets of corners) whenever a new
> cell is added in order to maintain the validity of the mesh, provided
> you wish to maintain the connectivity-data structure as faces are added
> and deleted.
> In the paper I linked-to above a 'lathe' is defined at each _corner_
> rather than at each edge. They present a concept for representing
> connectivity that generalizes several other data structures (including
> HE), and they discuss issues related to how a lath representation
> impacts boundary traversal or non-manifold edges. What is awesome is
> that I think this same concept extends to 3-manifold meshes as well (but
> I don't know if the authors ever developed that). Even if you do not
> extend your mesh library to 3D, I hope that you think about how it would
> be done and make sure the library is flexible enough to grow in that
> direction. This is another paper, which actually deals with both 2D &
> 3D meshes, but it nicely describes the kinds of issues I hope can be
> dealt with (
> I gather from the boost discussions that nobody has yet even settled on
> a boost-approved point & vector concept or class (uBlas has c_vector,
> and gil has point2 but that is kind of internal to the library and not
> intended to be for general use). Would this library include those?
> John Femiani
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