The VGM examples demonstrate use of VGM for conversion of existing native geometries.
E01: Geant4 -> Root
E02: Root -> Geant4
E03: Geant4 -> XML
E04: Root -> XML
The Geant4 basic example B4a source is used in E01, E02, E03 and the
ROOT rootgeom.C macro is used in E04. The geometry conversion
in E01, E02, E03 examples is performed in src/B4DetectorConstruction.cc class
and in E04 example in rootgeom.cxx.
See the code within the comment lines
// VGM demo
and
// end VGM demo
in these files.