extract surface face values with vtkGeometryFilter

Hi, I have my data in a vtkunstructuredgrid format. I want to assign a value to each grid cell, and then compute the corresponding surface values with vtkGeometryFilter. so in 3d, imagine a cube has a value assigned to it, and the outer face of the cube should give that value after vtkGeometryFilter.

I can do these kind of operations when everything is node based, so the question is if there is any equivalent that works on the cells instead of nodes. Any ideas how this can be done with VTK? Thanks!