CGAL users discussion list

[Sebastian Bachmann <>]

Hello,
No one has an idea? Is it not somehow possible to restrict nodes onto a 
surface? I.e. if I have the polyline of the surface's boundary, can I 
specify that all nodes must be on that surface?

For now I have written a function to go over all nodes and check if they 
are near such a boundary face and then "pull" the nodes onto that 
surface. However, there are certain edge cases were this then yields 
collapsed triangles etc. Thus, solving this during meshing would be a 
great enhancement.

Best,
Sebastian

On 25.04.2022 07:16, Sebastian Bachmann ( via cgal-discuss 
Mailing List) wrote:
> Hello,
>
> I created an image meshing tool, similar to the one given here in this 
> example code: 
> https://doc.cgal.org/latest/Mesh_3/Mesh_3_2mesh_3D_image_with_features_8cpp-example.html 
> with the only difference, that I extract the surface elements and not 
> write the full 3D mesh.
> I noticed, that on the image boundary, the vertices would be not exactly 
> on the face but roughly +- the relative error bound given in 
> create_labeled_image_mesh_domain. For examples, nodes on the xy plane at 
> z=0 are not on z=0 but for example -0.01 to 0.01. While the protected 
> polylines are exact and have always z=0.
> I created for example a mesh from the 420.inr example with the same 
> meshing criteria as given in the example and can see that behaviour there.
>
> While you can control the maximal deviation using the relative error 
> bound, there will always be some deviation. And if I set the relative 
> error bound too low, it seems the meshing never finishes.
> I wonder now, if it is possible to constraint the mesh (similar to the 
> 1d polylines), such that the vertices for facets on the image boundary, 
> are always exactly on the image boundary?
>
> Best,
> Sebastian