CGAL users discussion list

[Pierre Alliez <>]

hmmm... if your polygon is convex then you can certainly take advantage 
of this. I think you should take a look at some collision detection 
software http://www.cs.unc.edu/~dm/




Atul Thakur a écrit :
> I generated the Polyhedron by creating convex hull of my geometry as 
> follows.
>
>     CGAL::Object ch_obj;
>     Polyhedron_3 conv_hull;
>     CGAL::convex_hull_3(vertpset.begin(), vertpset.end(), ch_obj);
>     CGAL::assign (conv_hull, ch_obj);
>
>     Honestly speaking, I am not sure of primitives the facets are made
>     up of. Based on my understanding, they are not triangles. They are
>     general convex polygons.
>
>     The number of faces in my geometry is of the order of several
>     hundred thousands.
>
>     The queries are of the order of several thousands.
>
>     I hope, the information is sufficient.
>
>     thanks,
>     -Atul
>
>
>
>  
>
>
>
>
>     On Mon, Oct 20, 2008 at 3:29 PM, Pierre Alliez
>     
> <
>     
> <mailto:>>
>  wrote:
>
>         please provide us with more details:
>         - is your polyhedron triangular?
>         - what is its complexity in #triangles?
>         - how many queries do you want to compute?
>
>
>
>         Atul Thakur a écrit :
>
>             Hi Pierre:
>
>             Essentially, I want to know if P lies on surface of
>             polyhedron. If P is within or out pf polyhedron then P
>             doesn't lie on surface of polyhedron.
>             P can lie inside or outside but within a given tolerance.
>             So, it should look something like,
>
>
>             bool on_surface(Polyhedron_3 polyhedron, Point_3 P)
>             {
>               IF <fabs (distance_between(polyhedron, P))<1e-5>   THEN
>                   return TRUE
>               else
>                   return FALSE;
>             }
>
>             thanks,
>             -Atul
>
>             On Mon, Oct 20, 2008 at 2:59 PM, Pierre Alliez
>             
> <
>             
> <mailto:>
>             
> <mailto:
>             
> <mailto:>>>
>  wrote:
>
>                hi Atul,
>
>                I think the feature is not yet in CGAL - but I could
>             provide you
>                with hints about how to solve this.
>
>                first let's try reformulating your problem:
>
>                given a polyhedron (let's assume non self-intersecting
>             and watertight)
>                and a query point P, you want to know
>                - if P lies inside or outside the polyhedron.
>                - the closest distance form P to the polyhedron.
>
>                is this right?
>
>                Pierre
>                http://www-sop.inria.fr/members/Pierre.Alliez/
>
>
>                Atul Thakur a écrit :
>
>                    Hi all:
>
>                    I have a Polyhedron_3 and Point_3 and need to find
>             out if the
>                    point lies "on the" polyhedron or not <the answer
>             should be true
>                    if the point lies on the surface or very near to it,
>             should be
>                    false if it lies deep within or totally outside of
>             polyhedron>.
>                    I think one way of doing this is to determine the
>             distance of
>                    the point from each facet plane along its normal of the
>                    Polyhedron and then seeing if any of the distance is
>             less than a
>                    minimum bound value (say 1e-5). Is this the right way
>             or there
>                    exists some neat elegant function to do this check
>             <being a
>                    newbie, scanning 3500 pages of manual looks daunting
>             :)>? I saw
>                    some functions Polytope distance* but haven't quite
>                    understood(may be unrelated).
>
>                    Any pointers would be really helpful.
>
>                    sincerely,
>                    -Atul
>
>
>
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>
>
>
>         -- 
>         Pierre Alliez
>         INRIA Sophia Antipolis - Mediterranee
>         Project-team GEOMETRICA
>
>         http://www-sop.inria.fr/members/Pierre.Alliez/
>         Tel: +33 4 92 38 76 77
>         Fax: +33 4 97 15 53 95
>
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--
Pierre Alliez
INRIA Sophia Antipolis - Mediterranee
Project-team GEOMETRICA
http://www-sop.inria.fr/members/Pierre.Alliez/
Tel: +33 4 92 38 76 77
Fax: +33 4 97 15 53 95