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[goranw <>]

Hi Tang! The class CGAL::Mesh_3::Labeled_mesh_domain_3 is the domain oracle
to use for meshing multiple subdomains from polyhedra or implicit functions.
That domain class expects a generic function object that returns the
Subdomain_index containing a point p. 

In the mesh_implicit_domains.cpp example, the class
CGAL::Mesh_3::Implicit_vector_to_labeled_function_wrapper is used as the
function object. That is useful if your subdomains are described by implicit
signed distance functions. If your subdomains are polyhedra you can write a
similar class that takes a vector of Polyhedral_mesh_domain_3. See the
following post for an example:

http://cgal-discuss.949826.n4.nabble.com/Handling-sharp-features-with-multiple-input-polyhedra-tp3726552.html

These vector-to-labeled-function objects take at most 8 input subdomains
(signed distance or polyhedral mesh) and set one bit in a byte for each
subdomain that contains the requested point p. That way, the subdomains can
intersect and every represented combination gets a unique Subdomain_index.

Input meshes should be watertight and triangulated. The
Polyhedral_mesh_domain_3 checks if point p is inside by a
Point_inside_vertical_ray_cast. If two input polyhedra share a common facet
it should work fine as long as the facet is included in both of the
polyhedra. The mesher will produce a matched triangular interface between
the two tetrahedral subdomains.

You could also use implicit functions defined from your input meshes, as in
the mesh_polyhedral_implicit_function.cpp example, but that example is very
slow due to the way it's implemented.

Note that you may need to check how initial points are generated, they are
crucial for how the meshing works out...

Hope this helps!
Göran Wallgren



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