CGAL users discussion list

[Sebastian Bachmann <>]

Hi!

This is an image of a set of 20 and I can see this behaviour on 4 of 
them. On 420.inr it does not happen and the mesh looks good.
The code was compiled against 5.4 (1050401000).

If I look at the imges, I can not see any voxels standing out at the 
position - at least not more than on other places, where it works fine.
At least from the image, I cannot make out any particular feature that 
would cause that.

Is there any way to debug this and see what's going on?

Best,
Sebastian

On 24.05.2023 14:34, Sebastien Loriot ( via 
cgal-discuss Mailing List) wrote:
> Do you observe this behavior on all images or only a specific one?
> For example, when using 420.inr do you have such an issue?
>
> What could case such an over refinement (provided you are not using 
> master version of CGAL) is if the mesher is trying to respect some
> topological criteria (a very tiny handle for example, but that would be 
> surprising in an image).
>
> Best,
>
> Sebastien.
>
> On 5/24/23 14:14, Sebastian Bachmann ( via cgal-discuss 
> Mailing List) wrote:
> > Hi everyone,
> >
> > I have an image from which I want to create a coarse surface mesh.
> > The code I use for that is based upon the example 
> > mesh_3D_image_with_features.cpp, however it is adopted to then extract 
> > the surface and write an OFF file: 
> > https://gist.github.com/reox/0df1f446f0ff9d46e0688b60e8e858b8
> >
> > As you can see, the Mesh_criteria is set to a really coarse mesh. The 
> > input image (attached) I use has a voxel size of around 0.5mm and 
> > represents a proximal femur.
> > Now, for some reason, I get extremely fine triangle elements in 
> > certain places (see attached image).
> >
> > I find that peculiar, as the facet_distance is already quite large, 
> > and I thought that this might be the main issue here. I remembered, 
> > that also the relative_error_bound in the 
> > create_labeled_image_mesh_domain can have an influence, but reducing 
> > this rather creates a "spiky" mesh than removing those small elements. 
> > (Eventually when it is set to 0.1, the small elements vanish, but then 
> > the vertices are all over the place and not on the isosurface anymore...)
> >
> > Is there anything I missed here, maybe did I use wrong parameters? Or 
> > is there another way how I could produce such coarse meshes?
> >
> > Best,
> > Sebastian