CGAL users discussion list

Not only that the polygons must be valid, and this implies among the  
other that their boundaries must be counter clockwise, you should also  
use an exact-predicate and exact-construction kernel if you want to  
guarantee correct results. I've noticed that you fail to do this, and  
use 'double' number type instead. This last piece of information is  
repeatedly mentioned in the docs, lists, etc.

Quoting kyewong 
<>:

> Hi everyone, I think I've got the answer, though i still would like you guys
> to confirm that.
>
> I step into the "do_intersect" method when debugging and found that the two
> 2d polygons must be counter-clockwise before judging whether they intersect
> or not.
>
> So it should be compusory to make the two polygons CCW before using
> ""do_intersect"".
>
> Unfortunately, i failed to find the related comments/explanation in the CGAL
> document...
>
> It is still welcome to confirm whether the answer is true such that we can
> take care of it next time.
>
> Thanks!
>
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