How does the matlab contourf function work?

How does the matlab contourf function work? The function describes, "MATLAB® automatically selects the contour lines to display." -- but how does Matlab automatically select the lines? (Histogram? some other statistic?)

[Ameer Hamza]

The documentation does not specify how MATLAB calculates the contour lines internally. Also, you cannot see the internal implementation of the function, which draws the contour. However, you can specify the levels input of the contour function to set the value of contour lines manually.

[Jenna]

Yes. I know. I'm wondering if someone who works at matlab can describe the functionality a bit for me. Thanks

Answer 1

[darova]

I pretty sure that MATLAB checks each 'plane' (that close to some level) on intersection

Simply reducing the task to plane-plane intersection

clc,clear
cla
[X,Y] = meshgrid(-2:0.1:2);
Z = X.^2+Y.^2-3;
p = surf2patch(X,Y,Z);
surf(X,Y,Z,'edgeColor','none')
alpha(0.5)
f = p.faces;
v = p.vertices;
axis vis3d
for i = 1:size(f,1)
    ix = f(i,:);
    sgn = sign(v(ix,3));
    if abs(sum(sgn)) < 4              % if 'z' values have different sign
        patch('faces',ix,...
            'vertices',v,...
            'faceColor','none')
        pause(0.1)
    end
end