Cross Product to calculate Surface area

Ok. I have figure data(it has a lot of interpolating planets connected but when I use this method: ... no matter what the data in x, y, z... or figure it always bing up same number 113...ect.. kind a thinking it doesn't work with a direct input data or any figures.. help please.. cross product in order to correspond to my cartesian data or 3d interpolating surface figures..

[x,y,z] = peaks;

[m,n] = size(z);

area = 0; for i = 1:m-1 for j = 1:n-1 v0 = [x(i,j) y(i,j) z(i,j) ]; v1 = [x(i,j+1) y(i,j+1) z(i,j+1) ]; v2 = [x(i+1,j) y(i+1,j) z(i+1,j) ]; v3 = [x(i+1,j+1) y(i+1,j+1) z(i+1,j+1)];

a = v1 - v0; b = v2 - v0; c = v3 - v0;

A = 1/2*(norm(cross(a, c)) + norm(cross(b, c))); area = area + A; end end

fprintf('\nTotal area is: %f\n\n', area);