CGAL users discussion list

["Laurent Rineau (CGAL/GeometryFactory)" <>]

Le Tuesday, February 20, 2018 10:53:42 AM CET Kim Donghyeon a écrit :
> Hi, I have a question about CGAL volume meshing.
> 
> I’m working on generating head mesh from 3d medical image (already
> segemented).
 
> It is exactly same as brain mesh picture on 3D Mesh Generation user manual.
> (https://doc.cgal.org/latest/Mesh_3/index.html)
 
> My problem is, I could generate volume mesh, but thr surface of each label
> is very rough (not smooth)
 
> The resolution of segmented image is 256 * 256 * 256 (1mm * 1mm * 1mm). And
> also, I compared the result of Cleaver2 mesher and cgal mesher.
 
> I understand it could have different result. But cgal have rough surface
> mesh compared with the result of cleaver2.
 
> I think I missused volume mesh paramemter.
> 
> (my input data is:
> https://drive.google.com/file/d/1DUt-gSZ2uM8Rzv_9tfb80aWOmPLXbPl0/view?usp
> =sharing  )
 
> My code is based on “Mesh_3/mesh_3D_image_variable_size.cpp” and used
> 
>            double facet_angle = 30;
>            double facet_size = 2;
>            double facet_distance = 2;
>            Sizing_field cell_radius_edge_ratio(1.5);
> 
> To solve it, I already changed facet_size from 0.00001 to 2, but it does
> not affect the result (I did same value on facet_distance).
 
> Is it a normal situiation? and could you give an advice for me?

Hi Kim,

In the example code, replace the line:

    Mesh_domain domain(image);

with 

    Mesh_domain domain(image, 1e-6);


The default value for that second parameter is 1e-3, and that is too low for 
precise images like the one you use. That parameter sets the precision of the 
bissection algorithm used to compute intersections with the implicit surfaces 
of the image and query segments. I think the image 

> Also I just want to know the detailed parameter of the brain mesh which is
> on the top of 3D Mesh Generation document and chest mesh which figure
> number is 54.22

That image was created using the CGAL 3D demo (the code is in demo/
Polyhedron/), and I think the Mesh_3 uses 1e-6 for that parameter.

-- 
Laurent Rineau, PhD
R&D Engineer at GeometryFactory           http://www.geometryfactory.com/
Release Manager of the CGAL Project       http://www.cgal.org/