How to make emacs Semantic use the TAG file generated by GTAGS

My emacs version is 23.2.1 Although I used the following to change the backend to use GTAGS. (require 'semantic/db-global) (semanticdb-enable-gnu-global-databases 'c-mode) (semanticdb-enable-gnu-global-databases 'c++-mode) I tried to generate a GTAGS file to be used as a backend of semantic. However, everytime when I open a C file, Semantic is still parsing files without using the GTAGS file.

1. Is it possible to use the GTAGS file instead of the built-in parser of semantic? I found that the built-in parser is not very accurate.

2. Is it possible to use the GTAGS file without specifying the project scope? In my case, I tried to put GTAGS file in /usr/include which should be the standard include path of emacs. But Semantics is not using it.