CGAL users discussion list

[Andreas Fabri <>]

Note that there is also to_interval so that you can see how
good the to_double is.

andreas


Matthew Denno wrote:
> Thanks for the clarification.  I figured that once I convert my results 
> to double precision for output to shapefile they will no longer be 
> exact.  I need the intermediate results to be exact so that my 
> algorithms work properly, but think that converting to an approximate 
> solution just before writing the output will be okay.
>
> On Wed, Oct 21, 2009 at 9:47 AM, Laurent Rineau (GeometryFactory) 
> < 
> <mailto:>> wrote:
>
>     On Wednesday 21 October 2009 15:41:03 Matthew Denno wrote:
>      > Ah, perfect!  Thank you.
>      >
>      > On Wed, Oct 21, 2009 at 9:33 AM, Laurent Rineau (GeometryFactory) <
>      >
>      > 
>
>     
> <mailto:>>
>  wrote:
>      > > On Wednesday 21 October 2009 15:11:47 Matthew Denno wrote:
>      > > > 1) Is there a way to convert a
>     CGAL::Lazy_exact_nt<CGAL::Gmpq> value to
>      > > > double precision so that I can write to results out to a
>     shapefile?
>      > >
>      > > As for that question, use CGAL::to_double
>      > >
>      > >
>     http://www.cgal.org/Manual/3.5/doc_html/cgal_manual/Algebraic_foundations
>      > >_ref/Function_to_double.html
>
>     I send the mail too quickly. Be aware that the "conversion" done by
>     CGAL::to_double might not be exact. If you convert a CGAL::Gmpq or a
>     CGAL::Lazy_exact_nt<CGAL::Gmpq>, the CGAL::to_double function
>     template returns
>     an approximation of the number, with the best precision possible
>     with the type
>     "double".
>
>     --
>     Laurent Rineau, PhD
>     R&D Engineer at GeometryFactory          
>     http://www.geometryfactory.com/
>     Release Manager of the CGAL Project       http://www.cgal.org/
>     --
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