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[Sebastien Loriot <>]

The intersecton of a triangle with a tet is not always a triangle, it is
a polygon,

Doc says:
|Type1  | Type2 |Return Type: T...|
|Triangle_3 Tetrahedron_3 | 	Point_3, or Segment_3, or Triangle_3, or 
std::vector < Point_3 > |

https://doc.cgal.org/latest/Kernel_23/group__intersection__linear__grp.html


So it is most likely you miss some polygons.

Best,

Sebastien.

On 7/20/22 10:44, Marco Feder ( via cgal-discuss Mailing 
List) wrote:
> Dear all,
>
> I have two cubes (they’re coming from two cells of a 3D finite element 
> mesh) and a square (a 2D object) between the two, intersecting both of 
> them. I triangulated each cube with a Triangulation_3, and the square 
> with a Delaunay_triangulation_2.
>
> To compute the intersection of the square with the first cube, I do the 
> following: I loop over all tets of the triangulated cube, and for each 
> Tetrahedron I compute the intersection with a Triangle_3 coming from the 
> triangulated 2D square. Oftentimes I have correct results, but in some 
> scenarios I observe inaccurate results.
>
> For instance: for each cube, I computed the area of the part of square 
> inside it. The sum of these two areas should be precisely equal to the 
> area of the square (it is exactly *0.136900*), but it’s not. In 
> particular, the first area is *0.0237738*, and the second *0.0948123. 
> *Then the sum is *not 0.136900.*
>
> The following GitHub gist shows this: 
> https://gist.github.com/fdrmrc/49f397a5f72a7a00b1dfb992ab7babe1 
> <https://gist.github.com/fdrmrc/49f397a5f72a7a00b1dfb992ab7babe1> . The 
> output is the area of the intersection of the square with the second 
> cube. To get the first area, change at line 52 /pts_second_hex /with 
> /pts_first_hex./
>
>
> I can’t spot what is going wrong here.
>
> Best,
> Marco
>
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