Jane Tournois

[CGAL::Polygon_mesh_processing::isotropic_remeshing](https://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__meshing__grp.html#gaa5cc92275df27f0baab2472ecbc4ea3f) comes with a large set of options to activate/deactivate the different remeshing steps. You can use `parameters::do_split(false).do_collapse(true).do_flip(false).number_of_relaxation_steps(0).do_project(false)` to have only the collapse step

It is possible to remesh only a set of faces of the input surface, if you know how to select them

It works, and properly hides the protecting balls behind the cut plane. Thank you :-)

The predicate that has all the filter failures is `Compare_distance_3(point, segment, point)`, with 54.435 / 59.184 failures/calls while running `mesh_polyhedral_domain_with_features_sm.cpp`. Just note that the filter failures were already there before...

Let's reintroduce `sigma` to have this PR as a real bug-fix, and we'll see later if we remove it

Making more experiments on some user data, I found out that there is a trade-off in the choice of parameter `sigma` : - if too small we get the "stair-artefact"...

About the size of one voxel yes. But experiments did not really bring conclusions on weather we should use the minimal dimension, or maximal dimension, for the default value (?)

IIRC we had discussed with @MaelRL that it makes no sense to return NULL_VECTOR as the normal of a degenerate face. But the test seems to think the other way...

With commit b98ac1a0bbec, the protecting balls are displayed but they do not take the cut plane into account. All of them are displayed.

When opening a C3t3 with protecting balls, these errors repeat several times in the log: ``` GL ERROR : (ShaderCompilerSource : ErrorType) SHADER_ID_LINK error has been generated. GLSL link failed...