CGAL users discussion list

[Jane Tournois <>]

Hello,
can you please post some code and data so that we can try to reproduce 
your issue?
Best,
Jane

Le 07/02/2025 à 16:30, Sebastian Bachmann ( via 
cgal-discuss Mailing List) a écrit :
> Hi!
>
> I send this mail to the list yesterday, but apparently it was not 
> posted - but I also did not get a rejection mail? I suspect that 
> attachments are not allowed and get silently dropped?
> So here it is again with a link instead, sorry if it is now posted twice!
>
>
> I extended the example code from 
> mesh_3D_image_with_custom_initialization.cpp to mesh a multi-label 3D 
> image, i.e., I have for example 3 voxel values: 0 (background), 1 
> (some part), and 2 (some other part).
> This works reasonable well, but if I go down with the cell size, I get 
> weird artifacts in the surface of the mesh: at some random places, 
> "holes" appear (see screenshot here: 
> https://files.reox.at/.mesh/screenshot.png).
>
> I tried to track down the problem and it can be triggered by using 
> lloyd or odt optimization. When either of these are used, such holes 
> appear in my mesh (much much more in odt) - if I switch them off, 
> these holes are usually gone. But I found also images were such holes 
> appear in certain configurations, even without llyod or odt active.
> There, I can influence these holes by choosing a larger 
> relative_error_bound in create_labeled_image_mesh_domain (my default 
> is 1e-7) or by generating a new mesh, as there is some randomness in 
> initialize_triangulation_from_labeled_image (in my code, I specified a 
> seed for the PRNG and thus can reliably trigger it by choosing a 
> specific seed).
>
> Interestingly, it seems to appear more often when more than two labels 
> are used. Thus, in a binary image (only 0 and 1), this does not 
> happen. For example, if I take the same image with 3 labels and 
> replace all 2's by 1's, I get a much better mesh.
>
> Is there anything I may have missed to implement, for example during 
> the creation of the label domain? I can try to track down the problem 
> even more, but don't know at the moment where to look next and thus 
> would appreciate some guidance!
>
> Best,
> Sebastian
--
Jane Tournois, PhD
R&D Engineer at GeometryFactory
http://www.geometryfactory.com/