CGAL users discussion list

["Thomas Zangl - Home" <>]

Am Tue, 12 Jun 2007 09:28:16 +0200, schrieb "Andreas Fabri" 
<>:

Hi!

>Can you send me a minimal program so that I can reproduce
>and hopefully fix it.

I was unable to reproduce it with a simple program like this:
  Voronoi_Point p1(27, 37.9999);
  Voronoi_Point p2(27, 37.9999);
  Voronoi_Point p3(0.5, 0.5);
  Voronoi_Segment s1(p1, p2);
  cout << "Checking if " << p3 << " is on : " << s1;
  cout << " = " << s1.has_on(p3) << endl;

The bug happens in the code I sent before. I changed the code to
something like this:

//---------------------------------------------------------------------
bool hasIntersectionSegmentWithPoints(Voronoi_Segment s, VDPointContainer& 
points) {
  std::cout <<"Has the Voronoi_Segment an intersection with a ball center?" 
<< std::endl ;
  std::cout << "Segment: " << s << endl;
  /* rounding of the segment */
  Voronoi_Point pSource(round(CGAL::to_double(s.source().x())), 
round(CGAL::to_double(s.source().y())));
  Voronoi_Point pTarget(round(CGAL::to_double(s.target().x())), 
round(CGAL::to_double(s.target().y())));
  Voronoi_Segment sRound(pSource, pTarget);
  VDPointContainer::iterator it;
  for( it = points.begin(); it != points.end(); it++ ) {
    Voronoi_Point p1(CGAL::to_double(it->x()), CGAL::to_double(it->y()));
    cout << "Checking if " << p1 << " is on : " << sRound;
    cout << " = " << sRound.has_on(p1) << endl;
    if (sRound.has_on(p1)) {
      return true;
    }
  }
  return false;
}

After converting the "it" - Iterator to a point p1 it works. Strange?
Using directly *it (as previously shown) does not.  

Well,  I now noticed, that points which are supposed to lie on the ray
or segment are not classified as doing so. It seems that the .has_on()
check is so strict that rounding and calculation errors are causing
this (more or less) wrong result. 

So, how can I tell .has_on() to be not that strict? Can I tell it to
use some "error" of e.g. +- 0.002 ?
 
TIA,
-- 
----------------------------------------------------------------
,yours Thomas Zangl, Bakk.rer.soc.oec. - 

 -
- Freelancer - IT Consulting & Software Development -
- Student of Software Development-Economy (Master) -