CGAL users discussion list

[Mael <>]

Hello,

According to https://doc.cgal.org/latest/Triangulation_2/index.html#title0, "the triangulations of CGAL are complete triangulations which means that their domain is the convex hull of their vertices". Your polygon is non-convex, and this is why these four faces are there.

If you want to get the faces of the triangulation of your non-convex polygon, you can just start from a face that you know is inside (which can be found by using 'locate()' on a point you know is inside the polygon), and then using a spreading algorithm to "color" faces as long as they are not separated by a constrained edge.

Best,
Mael

On 13/08/18 06:21, Tekel wrote:

Hello, I've been struggling with this problem for a while now and the
information on the documentation and on the mailing list is not really
helpful... 

I want to tryangulate a Fisk Polygon (the one that looks like a crown, used
to proof Art Gallery theorem). Or any other non-convex polygon. Like this
one:
<http://cgal-discuss.949826.n4.nabble.com/file/t376023/polygon.png> 

However when I use the Triangulation provieded by   CGAL what I get is a
triangulation that includes incorrect faces as seen:

<http://cgal-discuss.949826.n4.nabble.com/file/t376023/tpolygon.png> 

Whilst the real triangulation is this one:
<http://cgal-discuss.949826.n4.nabble.com/file/t376023/geogebra-export.png> 

What is the easiest way to avoid having those extra 4 faces? (the ones in
the middle of each peak)

Thanks in advance



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