CGAL users discussion list

[houssen <>]

OK, so computing intersections directly is too complex to be realistic.
A way to do it would be to : compute closest distance, then project 
closest point (of line / polygon) on the line / polygon to intersect, 
right ?

Still need to check / understand if CGAL provides operators to compute 
closest distance and orthogonal projections: if somebody has some clue 
about that, I would appreciate to let me know.

Franck

Le 2015-11-13 3:22, zell_winston a écrit :
> Hi houssen,
> As far as my knowledge goes, geometric libraries dont usually provide
> the "Intersection of a pair of 3D lines". This is because the high
> possibility that 3D lines are not intersected at all.
> Instead, in computational geometry theory, we usually discuss the
> closest distance between two 3D lines. If the distance is smaller 
> than
> your predefined tolerance, you can assume it to be intersected.
> I haven't check the CGAL context for detail. Hope this quick message
> will help you.
>
> -------------------------
>
> zell_winston
>
> > FROM: houssen [1]
> > DATE: 2015-11-13 01:38
> > TO: 
> >
> >  [2]
> > SUBJECT: [cgal-discuss] Intersect lines with lines, and, polygons
> > with polygons in 3D space
> >
> > Hello,
> >
> > I need to intersect polygons, or lines, made of 3D points : is this
> >
> > possible with CGAL ?
> >
> > I am new to CGAL.
> >
> > First, I checked out the doc to intersect polygons, or lines, made
> > of
> > 2D points (x, y):
> > http://doc.cgal.org/latest/Sweep_line_2/index.html
> > http://doc.cgal.org/latest/Boolean_set_operations_2/index.html (in
> > particular section 3.3)
> > I went accross the tutorials without any problem using Point_2,
> > Segment_2 and Polygon_2.
> >
> > Then, I looked at the doc related to using 3D points instead of 2D
> > points (http://doc.cgal.org/latest/Polygon/index.html - section
> > 2.3): it
> > seems at least some operations are possible (for example,
> > is_simple).
> >
> > Now, I try to turn my basic tutorial into 3D space : basically, I
> > tried
> > to replace Point_2 by Point_3, Segment_2 by Segment_3, Polygon_2 by
> >
> > Polygon_3 the "naive" way, this seems not to be possible.
> > CGAL::compute_subcurves turns out to be unable to support
> > Segment_3,
> > right ? Also Polygon_3 does not seem to exist ! :D
> >
> > Can I compute intersections of polygons, or lines, made of 3D
> > points
> > (x, y, z) with CGAL ?
> >
> > Franck
> >
> > --
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