CGAL users discussion list

[Efi Fogel <>]

Please provide a complete stand-alone example that compiles.

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On Fri, 24 Nov 2023 at 23:44, Nicklas SB Karlsson <> wrote:

Have been able to make polygons with connected lines, circles and
boolean operations in between them. While possible to make polygons with
circular arcs using boolean operations of these it is not a desirable
solution. Preferred solution is of course to add lines and then needed
circular arcs.


Have code below that for some angles cases succeed making a polygon with
half circle and a line connecting the two endpoints example in attached
picture. It seems to work perfect for different angles then circle is to
the right the first if condition if(p2.y() < p3.y()) in code snippet
below. But for the second if condition if(p2.y() > p3.y()) it only seems
to work then pointing to the left the angle=PI but otherwise fail with
the error message at bottom. Suspect this is because something does not
fit perfectly together for example the points on the circle. Guess I am
not the first person try to do this. Anybody have any suggestions how to
make it work?


typedef CGAL::Exact_predicates_exact_constructions_kernel Kernel;
typedef Kernel::Point_2 K_Point_2;
typedef CGAL::Arr_circle_segment_traits_2<Kernel>::Point_2 Apoint_2;
typedef Kernel::Circle_2 K_Circle_2;
typedef CGAL::Gps_circle_segment_traits_2<Kernel> Traits_2; /* The
traits class Gps_circle_segment_traits_2 models the
GeneralPolygonSetTraits_2 concept.
                                                                      *
It enables Boolean set-operations on general polygons bounded by linear
segments or circular arcs. It should be parameterized with a kernel. */
typedef CGAL::General_polygon_set_2<Traits_2> Polygon_set_2;
typedef Traits_2::General_polygon_2 Polygon_2;
typedef Traits_2::General_polygon_with_holes_2 Polygon_with_holes_2;
typedef Traits_2::Curve_2                                 Curve_2;
typedef Traits_2::X_monotone_curve_2 X_monotone_curve_2;
typedef Traits_2::CoordNT                                 coordnt;

tool_type::tool_type(point_type pOld, point_type pNew)
{
   const double xOld = pOld.x;
   const double yOld = pOld.y;
   const double xNew = pNew.x;
   const double yNew = pNew.y;
   const double radius = 6;
   const double angle = atan2(yNew-yOld, xNew-xOld);
   const FT radiusFT = radius;

   {
     const K_Point_2 p0(xOld+radius*std::cos(angle + M_PI/2),
yOld+radius*std::sin(angle + M_PI/2)); // angle zero and pNew to the right
     const K_Point_2 p1(xOld+radius*std::cos(angle - M_PI/2),
yOld+radius*std::sin(angle - M_PI/2)); // of pOld arrangement below:
     const K_Point_2 p2(xNew+radius*std::cos(angle - M_PI/2),
yNew+radius*std::sin(angle - M_PI/2)); //   p0 p3
     const K_Point_2 p3(xNew+radius*std::cos(angle + M_PI/2),
yNew+radius*std::sin(angle + M_PI/2)); //   p1 p2

     {
       Polygon_2 pgn;
       const K_Circle_2 tool_circle(K_Point_2(xOld,yOld),
radiusFT*radiusFT);
       const K_Circle_2 tool_circle2(p2, p3, CGAL::COUNTERCLOCKWISE);
       toolFront = construct_polygon(tool_circle);
       monotone_curves_type cc;// = construct_circular_arc(tool_circle2,
radiusFT, p2, p3, CGAL::COUNTERCLOCKWISE); // Test function remove!!
then done
       if(p2.y() < p3.y())
       {
         const Apoint_2 p(p2.x(), p2.y());
         const K_Point_2 pRight(xNew + radius, yNew);
         const Apoint_2 r(p3.x(), p3.y());
         const K_Circle_2 c(p2, pRight, p3);
         const K_Point_2 center = c.center();
         const Apoint_2 q(pRight.x(), pRight.y());

         cc.x1 = X_monotone_curve_2(c, p, q, CGAL::COUNTERCLOCKWISE);
         cc.x2 = X_monotone_curve_2(c, q, r, CGAL::COUNTERCLOCKWISE);
         cc.valid = 2;
       }
       if(p2.y() > p3.y())
       {
         const Apoint_2 p(p2.x(), p2.y());
         const K_Point_2 pLeft(xNew - radius, yNew);
         const Apoint_2 r(p3.x(), p3.y());
         const K_Circle_2 c(p2, pLeft, p3);
         const K_Point_2 center = c.center();
         const Apoint_2 q(pLeft.x(), pLeft.y());

         cc.x1 = X_monotone_curve_2(c, p, q, CGAL::COUNTERCLOCKWISE);
         cc.x2 = X_monotone_curve_2(c, q, r, CGAL::COUNTERCLOCKWISE);
         cc.valid = 2;
       }
       pgn.push_back(cc.x1);
       pgn.push_back(cc.x2);
       pgn.push_back(X_monotone_curve_2(p3, p2));

       closed.insert(pgn);
     }
   }
}

terminate called after throwing an instance of
'CGAL::Precondition_exception'

   what(): CGAL ERROR: precondition violation!

Expr: cv1.point_position (p) == EQUAL && cv2.point_position (p) == EQUAL

File: /usr/include/CGAL/Arr_circle_segments_traits2.h

Line: 255

Aborted


For the curios persons it should be used to iteratively calculate tool
path for a CNC machine. If Successful I will try to add it to the CAM
module called path workbench in Freecad. At first tried to use the
builtin representation of material and tool shape but seems I got some
accuracy problem. Then I tried Open Cascade which Freecad use internally
or are built upon so to say but calculations where slow. So then I
decided to switch to CGAL as I had seen before it have an impressive
list of developers so guess it is the best possible to get.



Nicklas SB Karlsson

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