Accessing pgf nodes from inside Lua(La)Tex

Hi All,

I am writing a package with pgf/TikZ from making Nassi-Schneider diagramms.
I have the code working under XeLaTeX and wanted to refracture it to LuaTeX.
I have to admit that I am not very TeXian. 

My question is if I have the name of a pgf node how do I get at its coordinates from
within LuaTeX.

Or, is there a way to call pgf from directly inside LuaTeX.

What I am looking for is to have a LuaTeX call to get the coordinates.
The following code that I have is: 

	\pgfextracty{\YCoordinate}{\pgfpointanchor{\LastNode}{south}}

	where \LastNode is the Name of the pgf node and \YCoordinate is a dimension.

So my do I access pgf structures from in LuaTeX?

Any help or pointers would be appreciated.

It would help me, also, if someone could tell me how to access something I have defined
with \edef in LuaTeX

eg. 

in the TeX file 
\edef{\aValue}{tttt}