CGAL users discussion list

[Sebastian Bachmann <>]

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