physical path the public directory

How, from my controller, can I get the filesystem path to my rails app's 'public directory'? e.g.:

/users/eggie5/sites/rails_app/public

RAILS_ROOT/public

Sometimes I want/need an absolute path, so I add this to my config/ environment.rb

RAILS_FULL_ROOT = Pathname.new(RAILS_ROOT).realpath.to_s the public directory is then public = "#{RAILS_FULL_ROOT}/public"