CGAL users discussion list

[David Keller <>]

Thanks again for the fast reply and the precise answer.

Not to have the possibility to save the state in a persistent manner is 
a severe restriction for my intended application.

Aren't there considerations for/interests in Boost.Serialization 
(http://www.boost.org/libs/serialization/doc/index.html) as an 
alternative to the iostream-based approach of saving/loading objects in 
CGAL? Serialization of the arrangement DCEL through boost is possible 
out-of-the-box in a non-intrusive way. The Arrangement_2-template is 
serializable with slight changes or maybe some tricks involving the 
Arrangement_accessor (non-intrusive). The main issue remains the 
serialization of Core-numbers (or other algebraics), especially 
CORE::Expr, which in the most complex case involves the serialization of 
polynomials of rational-coefficients and a bunch of plain data. Overall 
there are lots of collateral pitfalls -- just look at the pointer 
arithmetics in Bezier_cache -- rendering the task not trivial either, 
but I see some light at the end of the tunnel ;-)

Efraim Fogel wrote:
> Again, the answer below is provided by Ron:
>
> It is impossible to use the I/O operations of arrangements of Bezier
> curves. While the Bezier curves supports operators >> and << (basically
> reading and writing its sequence of *rational* control points), it is
> difficult to output a point in a way that we can read and use afterwards
> (well, we can approximate it, but we loose its algebraic representation,
> if one was computed).
>
> You already suspected that these operations are "likely not trivial to
> add" for a point. Indeed they are.
>
> David Keller wrote:
>   
> > Hi,
> >
> > I'm appending this here, even though it is not directly related to the
> > above discussed issues:
> > What is required for the stream-IO of Bezier-curve-arrangements?
> >
> > ____
> >
> > typedef CGAL::CORE_algebraic_number_traits nt_traits;
> > typedef nt_traits::Rational rational;
> > typedef nt_traits::Algebraic algebraic;
> > typedef CGAL::Cartesian<rational> rational_kernel;
> > typedef CGAL::Cartesian<algebraic> algebraic_kernel;
> > typedef CGAL::Arr_Bezier_curve_traits_2<rational_kernel,
> > algebraic_kernel, nt_traits> traits;
> > typedef CGAL::Arrangement_with_history_2<traits> arrangement;
> >
> > ...
> > arrangement a;
> > ...
> >
> > std::ofstream outfile( "bezier.dat" );
> > outfile << a ;
> > ____
> >
> > For a first try I get stuck with some compile-time errors:
> >
> > /opt/CGAL-3.3.1/include/CGAL/IO/Arr_text_formatter.h: In member
> > function ‘void
> > CGAL::Arr_text_formatter<Arrangement_>::read_point(typename
> > Arrangement_::Traits_2::Point_2&) [with Arrangement_ =
> > CGAL::Arrangement_with_history_2<CGAL::Arr_Bezier_curve_traits_2<CGAL::Cartesian<CORE::BigRat>,
> > CGAL::Cartesian<CORE::Expr>, CGAL::CORE_algebraic_number_traits,
> > CGAL::Bezier_bounding_rational_traits<CGAL::Cartesian<CORE::BigRat> >
> >     
> > > ,
> > >       
> > CGAL::Arr_default_dcel<CGAL::Arr_Bezier_curve_traits_2<CGAL::Cartesian<CORE::BigRat>,
> > CGAL::Cartesian<CORE::Expr>, CGAL::CORE_algebraic_number_traits,
> > CGAL::Bezier_bounding_rational_traits<CGAL::Cartesian<CORE::BigRat> >
> >     
> > > > > ]’:
> > > > >           
> > libs/bspline/test/bezier_curve.cpp:391: instantiated from here
> > /opt/CGAL-3.3.1/include/CGAL/IO/Arr_text_formatter.h:371: error: no
> > match for ‘operator>>’ in ‘CGAL::Arr_text_formatter<Arrangement_>::in
> > [with Arrangement_ =
> > CGAL::Arrangement_with_history_2<CGAL::Arr_Bezier_curve_traits_2<CGAL::Cartesian<CORE::BigRat>,
> > CGAL::Cartesian<CORE::Expr>, CGAL::CORE_algebraic_number_traits,
> > CGAL::Bezier_bounding_rational_traits<CGAL::Cartesian<CORE::BigRat> >
> >     
> > > ,
> > >       
> > CGAL::Arr_default_dcel<CGAL::Arr_Bezier_curve_traits_2<CGAL::Cartesian<CORE::BigRat>,
> > CGAL::Cartesian<CORE::Expr>, CGAL::CORE_algebraic_number_traits,
> > CGAL::Bezier_bounding_rational_traits<CGAL::Cartesian<CORE::BigRat> >
> >     
> > > > > ]() >> p’
> > > > >           
> > When trying to hunt these down it seems _Bezier_point_2 is missing
> > some operator>> and operator<<. I cannot find these in the
> > distribution and they are likely not trivial to add from my point of
> > view.
> >
> > Kind regards,
> > David Keller
> >