How To Derive Surface Waviness Profile

Hello,

I have raw Excel data from white light interferometer and I am expected to perform a 2D gaussian filtering and derive surface waviness profile and roughness profile. How can I derive the waviness from the data and which equation should I use? I know the definition of waviness but I can not find a detail procedure to derive the waviness profile using Excel.

I hope some one will give me a clue.