Using interp2 function on a 2-dimensional sine wave

Hi, I have tried using the interp2 matlab function to interpolate a 2-dimensional sine wave.

Is this the result I should expect? Is there any way to compare the differences between the interpolated output to the original waveform?

Here's how the program goes:

% 2-dimensional interpolation

%original waveform

Fs=130; %sampling frequency

xi=(0:63); yi=(0:63);

[Xi,Yi]=meshgrid(xi,yi); % 64 samples

Z0 = sin(2*pi*30/Fs*Xi) + cos(2*pi*20/Fs*Yi);

%reduce sampling freq by 2 times

Fi=Fs/2; %sampling frequency/2

x=(0:63); y=(0:63);

[X,Y]=meshgrid(x,y); % 64 samples

Z = sin(2*pi*30/Fi*X) + cos(2*pi*20/Fi*Y);

Zi=interp2(xi,yi,Z,Xi,Yi,'bicubic');

%plot original waveform figure(1) surf(Xi,Yi,Z0); xlabel Xi ylabel Yi grid on title 'Original waveform'

%plot waveform on sample grid figure(2) surf(Xi,Yi,Z); xlabel X ylabel Y grid on title 'Original waveform on sample grid'

%plot Interpolated waveform figure(3) surf(xi,yi,Zi); xlabel xi ylabel yi grid on title 'interpolated waveform'