CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

You cannot do it exactly. You can only get an approximation.

Something like this should work

K::FT sqrt(K::FT v) {
  return K::FT(std::sqrt(CGAL::to_double(v)));
}

No guarantee that you will not have a problem with another
function not available for this number type.

Sebastien.


Kai WANG wrote:
> I'm sorry that I still don't quite understand how to modify it. Could 
> you please give a detailed explanation on the way to add a "sqrt" 
> function please? For example, given the following simple program which 
> has complile error, where should I add the "sqrt" function please?
> Thanks very much for ur help!
>
>
> typedef CGAL::Exact_predicates_exact_constructions_kernel K;
> typedef K::Line_3            Line;
> typedef K::Plane_3           Plane;
> typedef K::Point_3           Point;
> typedef K::Triangle_3        Triangle;
>
> int main(void)
> {
>   std::list<Triangle> triangles;
>   Point a(1.0,2.0,3.0);
>   Point b(4.0,0.0,6.0);
>   Point c(7.0,8.0,9.0);
>   Point d(8.0,7.0,6.0);
>   Point e(5.0,3.0,4.0);
>   triangles.push_back(Triangle(a,b,c));
>   triangles.push_back(Triangle(a,b,d));
>   triangles.push_back(Triangle(d,e,c));
>
>   Line line;
>   Plane plane;
>
>   // fit plane to whole triangles
>   
> linear_least_squares_fitting_3(triangles.begin(),triangles.end(),plane,CGAL::Dimension_tag<2>());
>  
>   // fit line to triangle vertices
>   linear_least_squares_fitting_3(triangles.begin(),triangles.end(),line, 
> CGAL::Dimension_tag<0>());
>  
>   return 0;
> }
>
>
>
>
> On Thu, Oct 6, 2011 at 11:31 PM, Sebastien Loriot (GeometryFactory) 
> < <mailto:>> wrote:
>
>     the PCA package make use of the square root function, so the underlying
>     number type in the kernel you are using should have a sqrt function
>     available.
>
>     Sebastien.
>
>
>
>     kyewong wrote:
>
>         Hi,
>         When I'm using the linear_least_squares_fitting_3 and
>         CGAL::Exact_predicates_exact___constructions_kernel as kernel,
>         there will be a
>         compile error as follows.
>         Could anyone tell me how to modify it if I want to use both of
>         them at the
>         same time please? Thanks very much!
>
>
>         1>F:\Program Files\CGAL-3.8\include\CGAL/__PCA_util.h(132) :
>         error C2665:
>         'sqrt' : none of the 3 overloads could convert all the argument
>         types
>         1>        F:\Program Files\Microsoft Visual Studio
>         9.0\VC\include\math.h(581): could be 'long double sqrt(long double)'
>         1>        F:\Program Files\Microsoft Visual Studio
>         9.0\VC\include\math.h(533): or       'float sqrt(float)'
>         1>        F:\Program Files\Microsoft Visual Studio
>         9.0\VC\include\math.h(128): or       'double sqrt(double)'
>         1>        while trying to match the argument list
>         '(CGAL::Lazy_exact_nt<ET_>)'
>         1>        with
>         1>        [
>         1>            ET_=CGAL::Gmpq
>         1>        ]
>         1>        F:\Program
>         
> Files\CGAL-3.8\include\CGAL/__linear_least_squares_fitting___triangles_3.h(57)
>         :
>         see reference to function template instantiation 'void
>         
> CGAL::internal::assemble___covariance_matrix_3&lt;__InputIterator,K&gt;(__InputIterator,InputIterator,__CGAL::Lazy_exact_nt<ET_>
>         [],const CGAL::Point_3<R_> &,const K &,const
>         CGAL::Triangle_3<R_> *,const
>         CGAL::Dimension_tag<dim> &)' being compiled
>         1>        with
>         1>        [
>         1>            InputIterator=std::list<__Triangle>::_Iterator<true>,
>         1>            K=CGAL::Epeck,
>         1>            ET_=CGAL::Gmpq,
>         1>            R_=CGAL::Epeck,
>         1>            dim=2
>         1>        ]
>         1>        F:\Program
>         Files\CGAL-3.8\include\CGAL/__linear_least_squares_fitting___3.h(58)
>         : see
>         reference to function template instantiation
>         'CGAL::Lazy_exact_nt<ET_>
>         
> CGAL::internal::linear_least___squares_fitting_3&lt;__InputIterator,Kernel&gt;(__InputIterator,InputIterator,__CGAL::Plane_3<R_>
>         &,CGAL::Point_3<R_> &,const CGAL::Triangle_3<R_> *,const K &,const
>         CGAL::Dimension_tag<dim> &)' being compiled
>         1>        with
>         1>        [
>         1>            ET_=CGAL::Gmpq,
>         1>            InputIterator=std::list<__Triangle>::_Iterator<true>,
>         1>            Kernel=CGAL::Epeck,
>         1>            R_=CGAL::Epeck,
>         1>            K=CGAL::Epeck,
>         1>            dim=2
>         1>        ]
>         1>        F:\Program
>         Files\CGAL-3.8\include\CGAL/__linear_least_squares_fitting___3.h(76)
>         : see
>         reference to function template instantiation
>         'CGAL::Lazy_exact_nt<ET_>
>         
> CGAL::linear_least_squares___fitting_3&lt;InputIterator,__Object,CGAL::Epeck,Tag&gt;(__InputIterator,InputIterator,__Object
>         &,CGAL::Point_3<R_> &,const Tag &,const Kernel &)' being compiled
>         1>        with
>         1>        [
>         1>            ET_=CGAL::Gmpq,
>         1>            InputIterator=std::list<__Triangle>::_Iterator<true>,
>         1>            Object=Plane,
>         1>            Tag=CGAL::Dimension_tag<2>,
>         1>            R_=CGAL::Epeck,
>         1>            Kernel=CGAL::Epeck
>         1>        ]
>         1>        F:\Program
>         Files\CGAL-3.8\include\CGAL/__linear_least_squares_fitting___3.h(93)
>         : see
>         reference to function template instantiation
>         'CGAL::Lazy_exact_nt<ET_>
>         
> CGAL::linear_least_squares___fitting_3&lt;InputIterator,__Object,CGAL::Point_3&lt;R_&gt;__,Tag>(InputIterator,__InputIterator,Object
>         &,Point &,const Tag &)' being compiled
>         1>        with
>         1>        [
>         1>            ET_=CGAL::Gmpq,
>         1>            InputIterator=std::list<__Triangle>::_Iterator<true>,
>         1>            Object=Plane,
>         1>            R_=CGAL::Epeck,
>         1>            Tag=CGAL::Dimension_tag<2>,
>         1>            Point=CGAL::Point_3<CGAL::__Epeck>
>         1>        ]
>         1>        .\linear_least_squares___fitting_triangles_3.cpp(33) :
>         see reference
>         to function template instantiation 'CGAL::Lazy_exact_nt<ET_>
>         
> CGAL::linear_least_squares___fitting_3&lt;std::list&lt;_Ty&__gt;::_Iterator<_Secure___validation>,Plane,CGAL::__Dimension_tag<dim>>(__InputIterator,InputIterator,__Object
>         &,const Tag &)' being compiled
>         1>        with
>         1>        [
>         1>            ET_=CGAL::Gmpq,
>         1>            _Ty=Triangle,
>         1>            _Secure_validation=true,
>         1>            dim=2,
>         1>            InputIterator=std::list<__Triangle>::_Iterator<true>,
>         1>            Object=Plane,
>         1>            Tag=CGAL::Dimension_tag<2>
>         1>        ]
>
>         --
>         View this message in context:
>         
> http://cgal-discuss.949826.n4.__nabble.com/compiling-error-of-__linear-least-squares-fitting-__3-under-Exact-predicates-__exact-constructions-kernel-__tp3878596p3878596.html
>         
> <http://cgal-discuss.949826.n4.nabble.com/compiling-error-of-linear-least-squares-fitting-3-under-Exact-predicates-exact-constructions-kernel-tp3878596p3878596.html>
>         Sent from the cgal-discuss mailing list archive at Nabble.com.
>
>
>
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> --
> Kai WANG