CGAL users discussion list

[落 域 <>]

Hey axnmol,

If I use the CGAL::collinear() with three Point_2 variables to check the point is or not collinear, the function tells me the point is not collinear with the segment, but when I use the CGAL::Segment_2::collinear_has_on() to check the point is or not collinear, and this function tells me the point is collinear with the segment.

Does the CGAL::collinear() has any difference with CGAL::Segment_2::collinear_has_on()?

void testPointCollinear()

{

    Point_2 startPoint(220.240005, -121.932671);

    Point_2 endPoint(-369.040009, -439.420013);

    Point_2 checkPoint(-49.0955925, -267.043030);

    CGAL::Segment_2<Kernel> testSegment(startPoint, endPoint);

    if (testSegment.collinear_has_on(checkPoint)) {

        std::cout << "points collinear" << std::endl;

    }

    else {

        std::cout << "points not collinear" << std::endl;

    }

}

And yes, you are right, I convert the Point_2 to the graphing software's struct, the struct defined by the float.

When I convert the Point_2 to the float struct, then convert it back to the Point_2, what should I do to provide the point is collinear with the segment, can you give me some suggest?

---

发件人: <> 代表 axnmol <>
发送时间: 2020年4月27日 7:58
收件人: <>
主题: Re: [cgal-discuss] 回复: 回复: 回复: difference for 2d polygons return incorrect polygon

 

Hey Luoyo,
I don't think the points you are expecting here are collinear. Thats why the
resultant polygon includes the point (220.240005 , -121.932671).
<http://cgal-discuss.949826.n4.nabble.com/file/t376209/Capture.png>
The graphing software you are using may be doing some rounding error as i
may not be using exact predicates. You can check if these points are
collinear in CGAL as :
 Point_2 x, y, z;
    x = Point_2(220.240005, -121.932671);
    y = Point_2(-369.040009, -439.420013);
    z = Point_2(-49.0955925, -267.043030);
 if (CGAL::collinear(x, y, z))std::cout << "yes";

Regards.



--
Sent from: http://cgal-discuss.949826.n4.nabble.com/

--
You are currently subscribed to cgal-discuss.
To unsubscribe or access the archives, go to
https://sympa.inria.fr/sympa/info/cgal-discuss