CGAL users discussion list

[Peter Hachenberger <>]

Hi Fred,

I would have provided such an interface if I a) had the time, b) it were less delicate. Mostly the
time still keeps me from doing it. One problem for me is also that I need to think about the interpretation of such a constructor, i.e., is the constructed polyhedron a solid and what do I do
with nested volumes? It's easiest to leave all volumes unselected and to the selection in a separate
step afterwards. Also you must not forget that nested shells demand the use of ray shooting to obtain
the nesting structure.

Peter

----- wrote: -----

To:
From:
Date: 03/25/2009 09:52PM
Subject: [cgal-discuss] polygon_soup_to_nef3


There are a number of converters, or helper classes, that construct a
valid Nef3 from various types of geometry. (shell_to_nef_3.h for shells,
vertex_cycle_to_nef_3.h for polygons, polyhedron_3_to_nef_3.h for CGAL
polyhedrons).

I myself have written something very similar to polyhedron_3_to_nef_3 for
converting my own manifold mesh representations into Nef polyhedrons. It
is quite delicate and involves getting all the incidence references,
indices and marks correct.

Now I'm thinking of supporting a more general class of input, namely sets
of vertices and sets of polygons as references to these vertices, where
the polygons can only intersect along their edge. Any spaces enclosed by
the input polygons would be marked with mark_bounded_volumes.

This seems like a pretty obvious class of input geometry for constructing
a Nef, hence the questions:

a) Is there any plan to provide this out-of-the-box? Of course you can
achieve this with a nary_union of individual polygons, but that's very
expensive.
b) Has anybody else done this?
c) Can anybody foresee any problems I may run into here?

Regards,
Fred

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