CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

On 12/17/2012 03:22 AM, Wang Hetao wrote:
> I encountered a problem when converting form Circular_arc_point_2 type to
> Point_2 in my program. What I consistently do in the past about this kind
> conversion is first converting the X and Y coordinates to double with
> CGAL::to_double(), then constructing a regular Point_2 with converted
> figures. This method is complex and imprecise, I wander whether there is a
> simple and more accurate method.
The coordinates of a Circular_arc_point_2 are algebraic numbers of
degree 2 (AN2) so there are no exact conversion to a Point_2 from any
Kernel, but a one instantiated with a FieldWithSqrt [1] (Core::Expr or
LEDA::Real).

If you want to rely on a double number type at the end you need
to_double or a tricky conversion based on the internal representation
of AN2 (Sqrt_extension [2])



> Another problem that confused me for a long time is CGAL lib borrows many
> data types form other libs. e.g., LEDA, GNU::GMP, CORE, and built-in number
> types of course. I think this may makes CGAL very hard to use.

What do you suggest? Rewrite our own number types? These libraries are
made by number types expert, and it would be a really bad idea to come
up with our own number types.


Sebastien.

[1]http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Algebraic_foundations_ref/Concept_FieldWithSqrt.html
[2] 
http://www.cgal.org/Manual/latest/doc_html/cgal_manual/NumberTypeSupport_ref/Class_Sqrt_extension.html

> many thanks for you reply!
>
>
>
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