The categories are retrieved from Drupal, but the search results are served by Google Search Application. GSA collections can be assigned to Faceted Search environments.
The Faceted Search module needs to be decoupled from the Drupal search.
Unpack in your modules folder (usually '/sites/all/modules/')
Enable under Administer > Site Building > Modules.
Here are some key features of "Faceted Search for Google Search Appliance":
· author facet
· content type facet
· taxonomy facet
· Drupal 6.x
· Drupal Faceted Search Module
· Drupal Faceted Search Module Patch