Rails 3.1 assets path

Hi all. I need directly access to the file.

Like this:

File.read(File.join(Rails.root,"public/stylesheets/head.css"))

Because I use https://github.com/mileszs/wicked_pdf/blob/master/lib/wicked_pdf_helper.rb

How can I get the real path name of file, where I use assets. I need not assets_path. I need real file path on file system.