Partial Alpha Wrapping

[kzayni]

Hello Everyone,

I want to do a partial wrapping of a geometry, like only the distorted region of a geometry. The idea is to wrap only the part that is distorted/deformed and leave the rest of the geometry untouched, since it is already clean.

Because alpha wrapping operates on the entire input, I attempted the following workflow:

1. clip the deformed region
   

2. fill the resulting hole
   

3. apply alpha wrapping only to the clipped part
   

4. clean the wrapped part
   

5. perform a Boolean union between the wrapped leading edge and the original geometry that I want to keep
   

The Boolean union completes successfully, but it consistently leaves a small seam between the two regions (I attached an example on a sphere). This happens because the wrapped geometry becomes slightly more inflated during the wrapping process. As a result, the two parts do not align perfectly, which prevents the combined mesh from being watertight. I have not been able to merge the pieces completely despite trying stitching, vertex merging, and local remeshing.

Do you have any recommendations for how to correctly combine an alpha-wrapped subregion with the original geometry so that the result is a single unified mesh without gaps?

[MaelRL]

There are undocumented snapping functions in Polygon Mesh Processing that you could try, see:

• https://github.com/CGAL/cgal/tree/main/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/Snapping headers (one is for vertex-vertex snapping, the other is for vertex-edge snapping)
  and
• https://github.com/CGAL/cgal/blob/main/Polygon_mesh_processing/test/Polygon_mesh_processing/test_pmp_non_conforming_snapping.cpp
• https://github.com/CGAL/cgal/blob/main/Polygon_mesh_processing/test/Polygon_mesh_processing/test_pmp_snapping.cpp
  for usage examples.