vol2mesh function, maxvol with 'cgalmesh' issue

[Laura Dempsey]

Hello,

We are creating mixed density meshes based on masks derived from MRI scans. Our final meshes have four different layers. When we create a high density mesh where each layer has the same maxvol settings, we get a nice result (HighDensity.png). However, we want to decrease the complexity of the mesh by reducing the density of the interior layers, so we have been using the 'cgalmesh' option to specify the maxvol for each layer. The issue we are having is that with the second layer, between maxvol = 1.7 and 2.2 the meshing does not work correctly and the layer is essentially eliminated/replaced by layer 1 (MixedDensityCSF_22.png). At maxvol = 1.6 and 2.3 the mesh once again appears reasonable (MixedDensityCSF_16.png and MixedDensityCSF_23.png).

Any ideas as to what could be causing this error? We can send the mask if that would help.

Best wishes,

Laura

[Qianqian Fang]

hi Laura

that's odd, looks like you've found a CGAL bug. I will
add it to the upstream bug list on github.

On the other hand, I have the following suggestions:

1. the best way to produce high-quality meshes and control the
mesh density is to use the volume->surface->surface smoothing
->tetrahedral mesh workflow. The surfaces derived from
cgalmesher are not as smooth. This, however, requires the
layer surfaces do not intersect each other. Try
v2s->sms->mergemesh->surf2mesh/s2m. This approach also
give you more freedom for density control. The label-specific
density control is achieved by setting the 4-th element in
each row of the regions input of surf2mesh (require the svn
version of iso2mesh). This also allows you to increase mesh
density near a specific region, for example close to the
source, by setting the 4-th column of the node input of
surf2mesh.

2. your head surface is very dense. When reducing mesh
density, I always coarsify more for smooth surfaces because
you don't loose much information. A high density surface
will increase the overall mesh size significantly.

3. try playing with opt.distbound and see if it has an impact
to the missing label. distbound by default is 1, set to a small
number for a refined boundaries (node grows rapidly).

Qianqian

Best wishes,

Laura

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[Laura Dempsey]

Hi Qianqian,

Thanks for the very quick reply. We will try these suggestions and see if we can get it to work. Many thanks for your help!

Kind regards,

Laura