How to do 3D Taylor to a matrix

Hi, I have a matrix of 2 variables (phi-->rows,teta-->columns) and the value for each position is the voltage received by a photodiode depending on this 2 variables. Both variables go from -60º to 60º and I would like to get a Taylor function of big order (10 or more) to represent the matrix (depending on phi an teta) and I don't know how. The photo is a representation of all the points of the matrix (300*300)

[Walter Roberson]

Is the function known, or are you trying to deduce it from measurements?

If you are trying to deduce it from measurements, you are effectively doing a multinomial fitting of high degree. The result is going to suffer from numeric roundoff problems quite a bit. The degree 10 taylor function in two variables would have 121 terms. Realistically, what would you do with it?