Node:Ellipse Intersections, Next:Solving Ellipses, Previous:Returning Elements and Information for Ellipses, Up:Ellipse Reference
bool_point_pair intersection_points (const Point& p0, const Point& p1)  const virtual function 
bool_point_pair intersection_points (const Path& p)  const virtual function 
These functions return the intersection points of a line with an
Ellipse . In the first version, the line is specified by the two
Point arguments.
In the second version, p.is_linear() must return true ,
otherwise, intersection_points() issues an error message and
returns INVALID_BOOL_POINT_PAIR .
If the line and the Ellipse e(origin, 5, 7, 30, 30, 30); e.shift(3, 0, 3); Point p0 = e.get_center().mediate(e.get_point(3)); Point normal = e.get_normal(); Point A = normal; A *= 2.5; A.shift(p0); Point B = normal; B *= 2.5; B.shift(p0); bool_point_pair bpp = e.intersection_points(A, B); bpp.first.pt.dotlabel("$i_0$", "rt"); Point C = e.get_point(15).mediate(e.get_point(11), 1.25); Point D = e.get_point(11).mediate(e.get_point(15), 1.5); Path q = C.draw(D); bpp = e.intersection_points(q); bpp.first.pt.dotlabel("$i_1$", "llft"); bpp.second.pt.dotlabel("$i_2$", "ulft");

bool_point_quadruple intersection_points (Ellipse e, [const real step = 3, [bool verbose = false ]])

const virtual function 
Returns the intersection points of two Ellipses . Two Ellipses
can intersect at at most four points.
Let bpq be the The step argument is used when the If the verbose argument is In [next figure]
, the Ellipse e(origin, 5, 2); Ellipse f(origin, 2, 5); bool_point_quadruple bpq = e.intersection_points(f); bpq.first.pt.dotlabel(1, "llft"); bpq.second.pt.dotlabel(2, "urt"); bpq.third.pt.dotlabel(3, "ulft"); bpq.fourth.pt.dotlabel(4, "lrt");
In [next figure] , e and f are coplanar, but don't lie in a major plane, have different centers, and only intersect at two points. Ellipse e(origin, 4, 2); Ellipse f(origin, 2, 5); f.shift(0, 0, 1); f.rotate(0, 15); f.shift(1, 0, 1); e *= f.shift(.25, 1, 1); e *= f.rotate(10, 12.5, 3); bool_point_quadruple bpq = e.intersection_points(f, true); bpq.first.pt.dotlabel(1, "urt"); bpq.second.pt.dotlabel(2, "ulft");
If the planes of the In [next figure]
, the two Ellipse e(origin, 5, 3); Ellipse f(origin, 2, 5); f.rotate(0, 0, 30); f.rotate(0, 10); f.rotate(45); f.shift(1.5, 1); bool_point_quadruple bpq = e.intersection_points(f, true); bpq.first.pt.dotlabel(1); bpq.second.pt.dotlabel(2); bpq.third.pt.dotlabel(3, "rt"); bpq.fourth.pt.dotlabel(4, "urt");  First point lies on the perimeter of *this. First point lies inside e. Second point lies on the perimeter of *this. Second point lies outside e. Third point lies outside *this. Third point lies on the perimeter of e. Fourth point lies inside *this. Fourth point lies on the perimeter of e.
In [next figure]
, the two Ellipse e(origin, 5, 3); Ellipse f(origin, 2, 5, 45); f.shift(0, 2.5, 3); bool_point_quadruple bpq = e.intersection_points(f, true); bpq.first.pt.dotlabel(1); bpq.second.pt.dotlabel(2);  First point lies on the perimeter of *this. First point lies outside e. Second point lies on the perimeter of *this. Second point lies outside e. Third intersection point is INVALID_POINT. Fourth intersection point is INVALID_POINT.
