Huayi，
In case you are wondering about how to model facets of triangles into a geometry surface in cgm, here's the hint:
Under cgm/geom/facet, the call FacetModifyEngine::build_cholla_surfaces() should give you a pointer to ChollaEngine.
From ChollaEngine you can get ChollaSurface pointer: ChollaEngine::get_surfaces( DLIList<ChollaSurface *> & cholla_surface_list )
For your case, there should be only one ChollaSurface generated. Get its EvalTool by get_eval_tool().
Then use the EvalTool to call project_to_facets(CubitVector &this_point,
CubitBoolean trim,
CubitBoolean *outside,
CubitVector *closest_point_ptr,
CubitVector *normal_ptr);
You should get all related info from this call then.
Hope it helps.
Jane