Where do I find the tables that a role has access to in Vertica?

I'm trying to use the System Tables to fetch some metadata about the whole Vertica cluster at a table level (including permissions). Where can I find the information about permissions required to SELECT on a table? I've poked around in the GRANTS and ROLES system tables, but I can't find any role->table mapping. I considered using HAS_TABLE_PRIVILEGE() but that does it on user level. I'd rather do it at the role level.