Normally Mmg3d preserve the boundary labels of the input domain and create a new surface of label 10 at the interface of 2 volume domains of label 3 (inside the level-set) and 2 (outside the level-set).
On the linked mesh, I see only one volume domain (of label 2).
An interactive way to check the mesh labels is to use the Medit software to visualize your mesh:
Each color is associated to a label. To print the label of an element inside your terminal, just click on the wanted element using
MAJ - left click. It prints something like that:
Picking result :
Triangle 7931 : 5497, 6695, 7974 ref : 3 [MAT03]
vertex 5497 : 0.009584 -0.001913 0.007286 ref 3
vertex 6695 : 0.020711 -0.002783 0.005265 ref 3
vertex 7974 : 0.014579 -0.002268 0.012605 ref 3
Inside Medit (and Mmg), we call the label “reference”, thus, here, the Triangle 7931 has the label (=ref) 3.
(Note that you can cut the mesh along a plane using the
F1 command and move the plane using
F2 and the mouse to see the volume mesh).