How to segment the convex part of a surface??

Hi,

How can I segment an area of a surface based on its normals?? or, in another word, how to segment the convex part of a surface??

for example: [X,Y] = meshgrid(-2:0.25:2,-1:0.2:1); ZZ = X.* exp(-X.^2 - Y.^2); surfnorm(X,Y,ZZ); [ix,iy,iz]=surfnorm(X,Y,ZZ); k=radtodeg(surfnorm(X,Y,ZZ));

Now, is it possible that I segment the convex part (the light green->red->light green part of the surface) by using k or [ix,iy,iz]?? I hope my question is clear!

TNX in advance :)