For mesh conversion, see

https://github.com/nschloe/meshio

tetgen calls examples:

C:\DATA\Programs\tetgen\build_dir\Release\tetgen.exe -p -q1.2/15 -a10.0 -Y -k -V skull.stl

where from my experience:

• -p to mesh surface from stl file
• -q{1}/{2} {1} from 1.2 to 2, {2} from 14 to 18
• -a{1} {1} -- linear tetra size
• -Y "to preserve surface"
• -k output to vtk
• -V verbose

file *.stl for tetgen must be a closed surface

CGAL useful utils:

• https://doc.cgal.org/latest/Polygon_mesh_processing/index.html#HFExample_2
  -- fill all the holes in a surface to make it closed surface
• https://doc.cgal.org/latest/Polygon_mesh_processing/index.html#RemeshingExample_1 -- remesh the surface -- make more homogeneous triangles, improve quality
• https://doc.cgal.org/latest/Mesh_3/index.html#title25 -- create mesh from 3D-image

For surface remeshing, surface *.off file for CGAL must be oriented, see orient_facets function in utils

My scripts:

• utils.py -- some useful functions to work with grids in python
• interpolate_materials.py -- restore cells info to a new grid from the initial grid using KD-tree from vtk
• remove_crossing_facets.py -- remove facets that are outer for some non-convex hull from a surface
• my_vtk_to_vlad_mesh.py -- convert vtk to DGM by Vlad format
• merge_surfaces.py
• refine_surfaces.py, extract_connected_components.py -- struggling to improve quality of skull mesh
• grid2surfaces.py -- extract surfaces that split one material from another, i.e for 3 materials there will be 6 surfaces (count outer space as material -1)
• grid2img.py -- convert a mesh to 3D image
• clear_initial_grid.py -- replace small connected components of materials in a mesh
• correct_3d_image.py -- smoothing 3D image