CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

The precondition is giving you the reason:

Explanation: The polygon has a wrong orientation.

Polygon_2 has a member function reverse_orientation() (that does not 
appear in the doc for some reason).

Sebastien.

On 12/19/2017 06:35 PM, xoru wrote:
> I always get :
> P = { Outer boundary = [ 4 vertices: (0 0) (1 0) (1 1) (0 1) ]
>    1 holes:
>      Hole #1 = [ 4 vertices: (0.4 0.4) (0.6 0.4) (0.6 0.6) (0.4 0.6) ]
>   }
> CGAL warning: check violation!
> Expression : valid_orientation
> File       : 
> /usr/include/CGAL/Boolean_set_operations_2/Gps_polygon_validation.h
> Line       : 778
> Explanation: The polygon has a wrong orientation.
> Refer to the bug-reporting instructions at 
> http://www.cgal.org/bug_report.html
> terminate called after throwing an instance of 
> 'CGAL::Precondition_exception'
>    what():  CGAL ERROR: precondition violation!
> Expr: is_valid_unknown_polygon(p, t)
> File: /usr/include/CGAL/General_polygon_set_on_surface_2.h
> Line: 48
> Aborted
> How union 2 polygons with holes or not?
> When I read from svg path I get any orientation. Is possible to change 
> orientation automaticaly?
> P have 2 holes. Q not.
> Anybody can help me and write completly example?