Adding a circle in a 3D surface plot, viewed in 2D

In the given code section, I am plotting some values as Z-coordinates in a surface plot, and then viewing it in 2D. I want to mark a circle on the same plot, given by the equation (x-13.125e-3)*(x-13.125e-3)+(y-5e-3)*(y-5e-3)=1.25e-3*1.25e-3. 'fplot' did not work, as I had assumed. How do I do it then?

figure(1)
[X,Y]=meshgrid(unique(CORD(:,1)),unique(CORD(:,2)));

Unrecognized function or variable 'CORD'.

surf(X,Y,damageFactorForAllNodesAtEndTimeStepReversed)
shading flat
colorbar("eastoutside")
xlabel("Length of sample")
ylabel("Width of sample")
title("Crack path at end time-step for homogeneous plate with soft inclusion")
view(2)
hold on
fplot(@(t) 1.25e-3*sin(t)+13.125e-3, @(t) 1.25e-3*cos(t)+5e-3)

If any other information is needed, do ask.

[Mathieu NOE]

hello

seems the code itself should work as in this example below

we cannot run exactly your code as you don't provide the data along , but the idea in itself is fine : just be aware that your circle may be hidden partially of completely depending of it's z values vs the surf z values : demo below

surf(peaks)
shading flat
colorbar("eastoutside")
xlabel("Length of sample")
ylabel("Width of sample")
title("Crack path at end time-step for homogeneous plate with soft inclusion")
view(2)
hold on
% fplot(@(t) 5*sin(t)+13, @(t) 5*cos(t)+25,'r'); % works , full circle is visible 
fplot(@(t) 5*sin(t)+18, @(t) 5*cos(t)+25,'r'); % works , but only a fraction of the circle is visible
% fplot(@(t) 5*sin(t)+25, @(t) 5*cos(t)+25,'r'); % doesn't work !! the
% circle is "below" in Z dir vs the surf object 

hold off

%axis equal 

Answer 1

[Walter Roberson]

If you are using fplot() then you need to ensure that some of your Z values are below 0 in the region you are drawing the circle in, as fplot() with two function parameters draws the resulting shape all at Z = 0 but surf() draws the Z values at the Z coordinate you pass in. If the Z coordinates you pass in are above 0 then the surface completely hides the fplot() drawn lines.

[X,Y,Z] = peaks();

surf(X*0.005, Y*0.005, (Z-1)*0.001, 'edgecolor', 'none');
view(2);
hold on
fplot(@(t) 1.25e-3*sin(t)+13.125e-3, @(t) 1.25e-3*cos(t)+5e-3)
axis equal
hold off

●

[Walter Roberson]

If you want to draw a circle "on top" of the surf() then you need to calculate the maximum Z coordinate drawn with surf(), and calculate specific X and Y coordinates for the circle and use plot3() specifying those X and Y together with a constant Z that is the maximum Z of the surf()

[Walter Roberson]

Of course there is the factor that the X and Y you are providing to surf() might happen to be a fairly different scale from the coordinates calculated for the circle in fplot(), so the circle might potentially be nearly invisible compared to the surf()