CGAL users discussion list

[Pablo Miranda Carranza <>]

I tried CORE::Expr in the data I had, I summarise here my findings and what
has worked for me:

Even if this worked in the sample program above, it did not work with the
whole data.

typedef CORE::Expr                                  ENT;
typedef CGAL::Simple_cartesian<double>    CK;
typedef CGAL::Simple_cartesian<ENT>        EK;
typedef CGAL::Segment_Delaunay_graph_filtered_traits_2<
CK,
CGAL::Field_with_sqrt_tag,EK,
CGAL::Field_tag
>  Gt;
typedef Extended_Segment_Delaunay_graph<Gt>   SDG_2;



Following your tip, I tried this, which worked (though it is quite slow):



typedef CORE::Expr                               ENT;
typedef CGAL::Lazy_exact_nt<ENT>        LENT;
typedef CGAL::Simple_cartesian<LENT>   CK;
typedef CGAL::Segment_Delaunay_graph_traits_without_intersections_2<
CK,
CGAL::Integral_domain_without_division_tag
>  Gt;
typedef Extended_Segment_Delaunay_graph<Gt>  SDG_2;


Here is a screenshot of the data:

<http://cgal-discuss.949826.n4.nabble.com/file/n4657381/Screen_Shot_2013-05-06_at_6.08.28_PM.png>
 




I am using the medial axis for doing some shape analysis on architectural
plans. Plans of buildings are usually difficult because they are full of
degenerate cases. The segment delaunay algorithms work fine in all the
number types I thought reasonable to use, but I have found problems with the
calculation of the circumcenters.

I found out that if I cast the input data to floats first,
Segment_Delaunay_graph_filtered_traits_2 works fine with all reasonable
types (it has no problems calculating the circumcenters). This is a
workaround that is reasonable in this case, since any meaningful dimensions
of a building will fit within a float (from thousands of meters to
millimeters). Otherwise the use of Core::Expr suggested by you works, but,
on the plan in the image above, it will only work when I use
Segment_Delaunay_graph_traits_without_intersections_2 (no filtered traits)
and CORE::Expr as the exact number type (Lazy_exact_nt<Core::Expr> works
fine).

Best,
Pablo





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