How to plot a line of zero value on a surface?

I used surf to generate a 3D surface and see it in 2D view (see below)

The dataset and code are also attached.

X=[0 0.25 0.5 0.75]';  % 4*1 vector
load Y.mat             % 36*4 matrix
load Z.mat             % 36*4 matrix

figure
set(gcf,'position',[100,100,1000,750]);
surf(X, Y, Z, 'EdgeColor', 'none', 'FaceColor', 'interp');
hold on;
colormap(coolwarm(256)); caxis([-0.35 0.35]); colorbar; 
patch([0,0.8,0.8,0],[0.8,0.8,0,0],[0,0,0,0],[1,1,1,1],'FaceAlpha',0.5,'EdgeColor',[0,0,0]);
grid off; view(2);

Now I want to plot the intersection of surface and zero-plane, can anyone help to with that? Thanks!

Answer 1

[Star Strider]

Use contour3 to draw the boundary (here a red line with 'LineWidth',5) —

LD1 = load(websave('Y','https://www.mathworks.com/matlabcentral/answers/uploaded_files/1230092/Y.mat'));
Y = LD1.Amp;
LD2 = load(websave('Z','https://www.mathworks.com/matlabcentral/answers/uploaded_files/1230097/Z.mat'));
Z = LD2.Pnet;

X=(ones(size(Z,1),1)*[0 0.25 0.5 0.75]);
  % 4*1 vector
% load Y.mat             % 36*4 matrix
% load Z.mat             % 36*4 matrix

figure
set(gcf,'position',[100,100,1000,750]);
surf(X, Y, Z, 'EdgeColor', 'none', 'FaceColor', 'interp');
hold on;
colormap(turbo(256)); caxis([-0.35 0.35]); colorbar; 
patch([0,0.8,0.8,0],[0.8,0.8,0,0],[0,0,0,0],[1,1,1,1],'FaceAlpha',0.5,'EdgeColor',[0,0,0]);
contour3(X, Y, Z, [0 0], '-r', 'LineWidth',5)
grid off 
view(-160,30)

% view(2);

The plane at ‘Z=0’ partially obscures the line.

.

[Ying Wu]

@Star Strider Thanks! When I convert to 2D view, the zero-line is partically covered, is there any method to show it completely?

[Star Strider]

Not if you want it exactly at zero.

One option —

LD1 = load(websave('Y','https://www.mathworks.com/matlabcentral/answers/uploaded_files/1230092/Y.mat'));
Y = LD1.Amp;
LD2 = load(websave('Z','https://www.mathworks.com/matlabcentral/answers/uploaded_files/1230097/Z.mat'));
Z = LD2.Pnet;

X=(ones(size(Z,1),1)*[0 0.25 0.5 0.75]);
  % 4*1 vector
% load Y.mat             % 36*4 matrix
% load Z.mat             % 36*4 matrix

figure
set(gcf,'position',[100,100,1000,750]);
surf(X, Y, Z, 'EdgeColor', 'none', 'FaceColor', 'interp');
hold on;
colormap(turbo(256)); caxis([-0.35 0.35]); colorbar; 
patch([0,0.8,0.8,0],[0.8,0.8,0,0],[0,0,0,0],[1,1,1,1],'FaceAlpha',0.5,'EdgeColor',[0,0,0]);
contour3(X, Y, Z, [0 0.005], '-r', 'LineWidth',5)
grid off 
% view(-160,30)
view(2);

figure
set(gcf,'position',[100,100,1000,750]);
surf(X, Y, Z, 'EdgeColor', 'none', 'FaceColor', 'interp');
hold on;
colormap(turbo(256)); caxis([-0.35 0.35]); colorbar; 
patch([0,0.8,0.8,0],[0.8,0.8,0,0],[0,0,0,0],[1,1,1,1],'FaceAlpha',0.5,'EdgeColor',[0,0,0]);
contour3(X, Y, Z, [0 0], '-r', 'LineWidth',15)
grid off 
% view(-160,30)
view(2);

This draws two contours, one at 0 and the other at 0.005. You can adjust one or both of those values as necessary to get the result you want. For example [1 1]*0.005 would draw one contour at 0.005. There must always be at least two elements to a vector fixing a contour level.

Another option (second figure) is just to thicken the line.

Providing higher resolution data could also work to make the line more easily visible, since this would reduce the need for contour3 to interpolate the level.

Still another option would be to nudge the zero-plane slightly lower so that it doesn’t hide the contour line.

.

[Ying Wu]

Thanks for detailed reply!

[Star Strider]

As always, my pleasure!