how to input image to 2 D gaussian

I need to implement a 2d gaussian fitting only want to fit a circularly-symmetric Gaussian.I am modifying the code given in:

http://in.mathworks.com/matlabcentral/fileexchange/37087-fit-2d-gaussian-function-to-data

by g.nootz.i need to put in the values of data obtained from my image. But I am not able to modify the code as stated in the comment by Nathan neff-mallon .Im a stuck in this part:

change line 38 to [X,Y] = meshgrid(x,y); where x and y a vectors with your x an y axis points change line 47 to Z = zdata; where zdata is a length(x) by length(y) matrix with the data you wish to fit such that zdata(i,j)=z(x_i,y_j).