Bridging two boundary cycles?

[pentacular]

Issue Details

Is there a supported way to close a hole that involves bridging two boundary cycles?

e.g., closing the base of a torus cut along its equator .

So far I cannot find any variant of triangulate_hole that will handle this kind of problem.

[MaelRL]

Assuming that you are manipulating a polygon mesh, if your boundaries are conformal (i.e., the edges of the boundaries match), you can use PMP::stitch_borders.

If they do not match, you can try to match them with the undocumented snapping functions, see https://github.com/CGAL/cgal/blob/master/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/Snapping/snap.h#L1422 and the files within this folder.

If your hole is too big for snapping to work, there is no out of the box solution currently. The way we usually hack around in this case is to find two good pairs of consecutive points (each pair having one vertex on each boundary), and then manually add a quad through Euler::add_face() to go back to a single border onto which you can call triangulate_hole()-like functions. A criterion to create that quad could be something like "minimize the square of the distances for each pair".