I know that is a stupid question, but will be very useful for me.
maybe this is not the best site to do this question, but i think that this can be useful for someone who use OCC and netgen.
With Netgen we can found 2 "layers" to wrap OCC geometries for meshing. With nglib (nglib.h) we can load a geometry and mesh it, but if we want to do something with the geometrys (mesh subdomains, merge meshes, ...) we have to use occgeom (occgeom.hpp) and some classes from OpenCascade.
nglib uses the following variable types for geometries and meshes: Ng_OCC_Geometry and Ng_Mesh.
occgeom uses OCCGeomtry and Mesh. Here comes the stupid thing... I have some problems to understand this in C++... The variable types for geometries and meshes in nglib are only pointers to the OCCGeometry and Mesh variables!!