/// Returns true if the segment crosses a boundary line of the polygon.
/// It is not enough for the segment to simply intersect the boundary
/// line -- it must cross it such that the segment extends to both inside
/// and outside of the boundary of the polygon.
bool intersects_proper(const Segment_2& segment, const Polygon_2& polygon)
{
static log4cplus::Logger logger = log4cplus::Logger::getInstance("tiler.intersects_proper");
Point_2 seg_pts[] = { segment.source(), segment.target() };
// Get intersection points between segment and polygon
LOG4CPLUS_TRACE(logger, "Doing a line sweep: " << pp(segment));
list<Segment_2> segments(polygon.edges_begin(), polygon.edges_end());
segments.push_back(segment);
list<Point_2> points;
get_intersection_points(segments.begin(), segments.end(), back_inserter(points), true, false);
CGAL::Bounded_side side1 = polygon.bounded_side(seg_pts[0]);
CGAL::Bounded_side side2 = polygon.bounded_side(seg_pts[1]);
LOG4CPLUS_TRACE(logger, "Checking with cross checker");
if (points.size() == 0)
return false;
Cross_checker checker;
checker.add(side1);
checker.add(side2);
if (checker.crosses())
return true;
if (points.size() == 1)
return false;
points.push_back(seg_pts[0]);
points.push_back(seg_pts[1]);
points.sort();
list<Point_2>::iterator it0 = points.begin();
list<Point_2>::iterator it1 = it0;
++it1;
while (it1 != points.end())
{
const Point_2& p0 = *it0;
const Point_2& p1 = *it1;
// find an intermediate point and test for where it is
Point_2 midpoint((p0.x()+p1.x())/2.0, (p0.y()+p1.y())/2.0);
checker.add(polygon.bounded_side(midpoint));
if (checker.crosses())
return true;
++it0;
++it1;
}
return false;
}
