ios - MKPolygon 交点

Question

我正在MKmapView像这样绘制一个多边形：

CLLocationCoordinate2D  points2[[swaping count]];
points2[0] = CLLocationCoordinate2DMake([[[swaping objectAtIndex:0] valueForKey:@"lat"] doubleValue], [[[swaping objectAtIndex:0] valueForKey:@"lng"] doubleValue]);
points2[1] = CLLocationCoordinate2DMake([[[swaping objectAtIndex:1] valueForKey:@"lat"] doubleValue], [[[swaping objectAtIndex:1] valueForKey:@"lng"] doubleValue]);
points2[2] = CLLocationCoordinate2DMake([[[swaping objectAtIndex:2] valueForKey:@"lat"] doubleValue], [[[swaping objectAtIndex:2] valueForKey:@"lng"] doubleValue]);
points2[3] = CLLocationCoordinate2DMake([[[swaping objectAtIndex:3] valueForKey:@"lat"] doubleValue], [[[swaping objectAtIndex:3] valueForKey:@"lng"] doubleValue]);

poly2 = [MKPolygon polygonWithCoordinates:points2 count:4];
[self.mapView addOverlay:poly2];

在那之后，我可以拖我的观点。我想知道如何检查多边形上折线的交点（边缘）？