How do I cut a surface in Matlab plot?

Hello,

I have a function f(x) which is in 2D, allowing me to make surf plot. To make the surf plot, I discretise the space and do 2 for loops over the x and y indecies to get a matrix of Z values. I then use the surf command to plot this surface.

However, I would like to cut the surface at all Z values above a critical value to produce a smooth boundary. I do this by simply removing the values of the Z matrix which are above a critical value by setting those to "nan".

When I plot this new Z matrix (with some enteries as "nan") , I get a choppy border, see the figures below. I know this is because my space is discretised into a finite grid of points, and I could just increase the number of points, however since the function is expensive to evaluate, I don't want to do this methid.

Is there another way to plot the surface with a smooth boundary?

Many thanks.

Answer 1

[darova]

Do you have a contour? Green line?

[x,y,z] = peaks(20);

    % some contour data
data = [-0.3907    1.5591
   -1.8039    0.6908
   -0.8456   -0.8716
    1.7243   -0.8535
    1.3515    0.7998];
x1 = data(:,1);
y1 = data(:,2);
gd = [2; length(x1); x1(:); y1(:)];     % geometry
dl = decsg(gd);                         % decomposition of geomtry
[p,e,t] = initmesh(dl);                 % mesh
z1 = interp2(x,y,z,p(1,:),p(2,:));      % get 'z' coordinate

ff.vertices = [p' z1(:)];
ff.faces    = t(1:3,:)';
ff.facecolor= 'y';

surf(x,y,z,'facecolor','none')
line(x1,y1,y1*0+5,'linew',3)
patch(ff)

axis vis3d