CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

T.vanLankveld wrote:
> As an additional note, I did some tests on my data and found something I
> thought was weird, but this may seem like a beginners mistake to the more
> veteran CGAL-programmers:
>
> I did the following tests on each triangle in the Delaunay triangulation
> before using the points to construct the alpha-shape:
>
> - triangle.is_degenerate()
> - CGAL::collinear(p0, p1, p2)
> - Rational rdx1 = Rational(p1.x())-Rational(p0.x()), rdy1 =
> Rational(p1.y())-Rational(p0.y());
>   Rational rdx2 = Rational(p2.x())-Rational(p0.x()), rdy2 =
> Rational(p2.y())-Rational(p0.y());
>   rdx2*rdy1 == rdx1*rdy2
> - NumberType dx1 = p1.x()-p0.x(), dy1 = p1.y()-p0.y();
>   NumberType dx2 = p2.x()-p0.x(), dy2 = p2.y()-p0.y();
>   CGAL::compare(dx2*dy1, dx1*dy2) == CGAL::EQUAL
> - dx2*dy1 == dx1*dy2
>
> Only the last two checks returned true when using a
> Filtered_kernel<Cartesian<double>>.
> Rational here is Quotient<MP_Float> and NumberType is double.
Do you have a minimal example?