CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

Please read again this example:

http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Box_intersection_d/Chapter_main.html#Section_62.5

First you filter intersection by simply doing Bbox intersections
and then in case of overlap of bboxes YOU call do_intersect.
Note that a axis-aligned bboxes overlap test is simple comparison
of bounds and is really fast.

Sebastien.


On 10/17/2011 11:28 PM, Graviton wrote:
> Thanks, but won't that be a bit slow? Because for every intersection,
> you need to box_self_intersection_d
> <http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Box_intersection_d_ref/Function_box_self_intersection_d.html#Cross_link_anchor_1717>
>  once,
> and then do_intersect a second time, would that means that I am actually
> computing the intersection one more time than necessary?
>
> On Tue, Oct 18, 2011 at 2:20 PM, Sebastien Loriot (GeometryFactory) [via
> cgal-discuss] <[hidden email]
> </user/SendEmail.jtp?type=node&node=3914344&i=0>> wrote:
>
>     On 10/17/2011 11:15 PM, Graviton wrote:
>
>      > Hello, I read your link, and look back at the do_intersection API, I
>      > don't think do_intersection actually takes in a functor, just
>     like how
>      > box_self_intersection_d
>      >
>     
> <http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Box_intersection_d_ref/Function_box_self_intersection_d.html#Cross_link_anchor_1717>
>     does.
>      > Or is it that one needs to use box_self_intersection_d
>      >
>     
> <http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Box_intersection_d_ref/Function_box_self_intersection_d.html#Cross_link_anchor_1717>
>     in
>      > this case? But isn't box_self_intersection_d
>      >
>     
> <http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Box_intersection_d_ref/Function_box_self_intersection_d.html#Cross_link_anchor_1717>
>     is
>      > supposed to be used for proximity computation, and used when
>     there are
>      > complicated geometries?
>      >
>     The call to do_intersect must be done by you in the functor.
>     The functor is called each time the bounding boxes intersect.
>
>     Sebastien.
>
>
>      > On Tue, Oct 18, 2011 at 1:13 PM, Sebastien Loriot
>     (GeometryFactory) [via
>      > cgal-discuss] <[hidden email]
>      > </user/SendEmail.jtp?type=node&node=3914328&i=0>> wrote:
>      >
>      >     Have a look at this chapter:
>      >
>      >
>     
> http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Box_intersection_d/Chapter_main.html
>      >
>      >     and in particular the following example you can adapt
>      >     to polygon. Note that you can also pass a functor instead
>      >     of a function.
>      >
>      >
>     
> http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Box_intersection_d/Chapter_main.html#Section_62.5
>      >
>
>      >
>      >
>      >     Sebastien.
>      >
>      >     On 10/17/2011 07:45 PM, Graviton wrote:
>      >
>      > > I have a list of polygons, and I want to check whether any of
>      >     them intersect
>      > > with others or not ( predicate is sufficient, I just want to know
>      >     whether A
>      > > polygon intersects with B, that's it).
>      > >
>      > > And since I have a list of polygons, I want to use do_intersect
>      >     and I want
>      > > to keep the index of the intersected polygons. It would be
>     great if
>      > > do_intersect also accepts a functor, that is called when an
>      >     intersection
>      > > happens, so that I can store the index of the polygon somewhere.
>      > >
>      > > --
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>      > >
>      >
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