CGAL users discussion list

[Nicklas SB Karlsson <>]

Have been fighting the problem to calculate the intesection points
betweeen general polygon outer boundary and other general polygon outer
boundary, curve or monotone curve.

Are able to calculate intersection between
CGAL::Gps_circle_segment_traits_2<Kernel>::Curve_2 used to construct
polygon with CGAL::compute_intersection_points(...) function.
Are however not able to extract the curves of same type as used to
construct general polygon and are only able to extract
CGAL::Gps_circle_segment_traits_2<Kernel>::X_monotone_curve_2 from
polygon. But CGAL::compute_intersection_points(...) function does not
accept these monotone curves as input arguments.

Have also tried to insert polygon segments into an
CGAL::Arrangement_2<CGAL::Gps_circle_segment_traits_2<Kernel>> but for
this arrangement it is not possible to iterate thru the vertices.

General polygon does not have the has_on_boundary(...) function so
using this is not possible either.

Pretty sure the boolean set operation difference that do work as
expected calculate the intersection point internally so it must be
possible in some way?

Read something about CGAL::Arr_observer<Arrangement> and get a
notification with intersection points would be possible?



For the curious it should be used to iteratively calculate tool path
then machining a pocket on a CNC machine. In each step tool is moved
forward a small step then intersection points are calculated to
determine direction for the next step to keep tool engagement angle
constant. Then this have been done boolean operation difference is used
to remove material from the polygon representing stock material using
the polygon representing tool.
Guess or are pretty sure the boolean set operation difference calculate
the intersection points internally so if possible to get these it
should most certainly be the ideal solution with best performance.


Regards Nicklas Karlsson