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["Sebastien Loriot (GeometryFactory)" <>]

On 09/26/2014 05:55 PM, shebbycat wrote:
> Thanks for the response, Sebastien.
>   Plane_3::has_on_positive_side(origin)  seems like it will do the
> trick.  However when I use Exact_predicates_exact_constructions_kernel
> seems I can no longer convert a Polyhedron/3 to a Nef/Polyhedron3.   My
> initial polyhedron is generated by Random_points_in_sphere_3 followed by
> a Delaunay triangulation.

Did you also changed the Polyhedron Kernel?

Sebastien.

> At a high level I start with a Polyhedron_3 random sphere, define a
> clipping plane, clip, convert to Nefpolyhedron3, clip, then convert back
> to a Polyhedron_3 for rendering in OpenGL.    Could there be a better
> way of approaching this process?
>
> From: "Sebastien Loriot (GeometryFactory) [via cgal-discuss]" <[hidden
> email] </user/SendEmail.jtp?type=node&node=4659901&i=0>>
> Date: Monday, September 22, 2014 at 7:23 AM
> To: Scott Shebby <[hidden email]
> </user/SendEmail.jtp?type=node&node=4659901&i=1>>
> Subject: Re: Iterative Applications of 3D Boolean Operations on Nef
> Polyhedra
>
> On 09/21/2014 03:12 AM, shebbycat wrote:
>
> > Hi everyone,
> >
> > I'm new to CGAL and quite grateful for its existence!  I've built an
> > application that iteratively clips a 3D Nef Polyhedra with a plane, for a
> > specific application.  For example, I define a clipping plane which
> > intersects a polyhedron (with its center at 0,0,0) and clip, rotate by some
> > degrees, clip again, and so on.  When its done I convert it back to a 3D
> > polyhedron and render it in OpenGL.
> >
> > My first question is that this process is really slow.. like taking a couple
> > seconds per clip.  My kernel is:
> > typedef CGAL::Extended_cartesian< CGAL::Gmpq> K2;
> Try CGAL::Exact_predicates_exact_constructions_kernel instead of K2.
>
> Do you have a geometric properties for your set of clipping planes?
> (like defining a convex volume)?
>
>
> > My second question is that sometimes after my clip process Ive inadvertently
> > clipped the origin side of the polyhedron instead of the "outer" side of the
> > intersection.  Id like to always preserve the portion of the poly that
> > contains the origin.  Ive tried grabbing the volume handle for the origin
> > point, but not sure how to use it properly.
>
> try using Plane_3::has_on_positive_side(origin)
>
> http://doc.cgal.org/latest/Kernel_23/classCGAL_1_1Plane__3.html#a2ca90cac980833ff38dd12dcb9858baf
>
> Sebastien.
>
> > Is there anything I can do to speed the clipping up, and whats the best way
> > to check that my intersection will preserve the correct side of the poly?
> >
> > Thanks!
> >
> >
> >
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> Operations on Nef Polyhedra
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