CGAL users discussion list

[Efraim Fogel <>]

Dennis Schieferdecker wrote:
> Ophir Setter schrieb:
>   
> > The problem is probably that 0.01 is not translated to 1/100 in an
> > exact manner.
> > You should construct 1/100 using a rational number constructor;
> > probably something like: Kernel::FT(1, 100).
> >
> >     
> Thanks that did the trick (and significantly decreased the number of
> faces with my larger setup). Maybe you could help me with another type
> problem later in my program?
>
> After having computed the circular arrangement, I need to perform
> several calculations with the vertices of the arrangement. Unfortunately
> the points they represent are of type Traits::Point_2 instead od
> Kernel::Point_2 and use a different numerical type ( Traits::CoordNT,
> i.e. one_root_number< Kermel::FT >). Here, I run into a problem, since I
> cannot perform the typical operations I can with type Kernel::Point_2
>   
What operations are you missing?
> and by converting Traits::Point_2 to Kernel::Point_2 I losse my
> exactness. In principle I need to compute the point that lies in the
> middle of two vertices and the orientation of three vertices.
> Also, a related problem is the compuatation of the intersection point of
> one edge E of a face of the arrangement with a line L. Line L is defined
> by two points of type Traits::Point_2 and Edge E is represented as
> X_monotone_curve using a number type Traits::CoordNT. Now, the
> intersection functor requires two lines of the same type. Thus I have to
> represent line L as X_monotone_curve. Unfortunately, there is no way to
> contruct one of two points of type Traits::Point_2, only of type
> Kernel::Point_2.
>   
The traits supports curves that are either circular arcs or segments the 
coefficients of which are rational, and it contains a functor that 
computes the intersection between any pairs of curves supported by the 
traits. Intersections between segments the coefficients of which are not 
rational is not supported, at least not by the traits class.
> Is there another (obvious) transformation I am missing, or are the
> Traits::Point_2 the "end of the road" with regards to the reusability in
> further calculations?
>
> bye
> Dennis
>   
There are two traits that support circular arcs and segments in the 
arrangement package, namely, Arr_circle_segment_traits_2 and 
Arr_circular_line_arc_traits_2. The latter may support more operations, 
as it is based on a CircularKernel.

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