Dependent variable as a function of coordinates

Hello
I've solved 2D PDE problem and I've got distribution field of the dependent variable (_u_).
Now I need global function that should use solution _u_ as a function of coordinates.
I can't understand how I can get scalar u(x,y) in global definitions.

I use "data export" of _u_ to the text file then import that file to the global interpolation function and get function of two coordinates. But I hope, there must be the easier way.

Thanks a lot.