Triangle.NET and touching polygons

Question

How do I triangulate a polygon with an hole like the one below using Triangle.NET?

I need the green area covered by triangles. I guess I need to split the right segment of the outer contour on the touch point but afterward I don't know if I need to combine the two contours into one (with a duplicated point at the black square?) or keep them separated.

Thanks.

Answer 1

In Triangle (which Triangle.NET is just a port of), you define this with connected input segments and specify a "hole" in the domain to clean out the interior triangles that you don't need. I created a ".poly" input file for triangle with a similar geometry:

8 2 0 0
1 1.0 1.0
2 -1.0 1.0
3 -1.0 -1.0
4 1.0 -1.0
5 1.0 0.0
6 0.5 0.5
7 0.0 0.0
8 0.5 -0.5
9 0
1 1 2
2 2 3
3 3 4
4 4 5
5 5 1
6 5 6
7 6 7
8 7 8
9 8 5
1
1 0.5 0.0

The input looks like this

.

You can see the small "x" in the inner box indicating that region is a hole (and will not get triangulated).

Meshing with triangle gives you something like this

where you see a domain corresponding to the green area in the post get triangulated.