How to properly color a surface in two different colours using surf function?

Dear MATLAB users,

I would like to color a surface in two different colours using surf function. I have a surface which is defined as . For f(x,y) <= 2, I want to use blue, while for f(x, y) > 2, red.

Here are my codes and the results. The fig. makes me satisfied when I am looking in MATLAB. But when I export my fig. to PDF-file, I find that the surface of f(x,y) <= 2 is plotted twice using two different colors (red and blue). I understant that it is normal but this is not I want.

clearvars; clc; close all; fclose all; format short; format compact;

x = linspace(-0.5, 0.5, 21);

[X, Y] = meshgrid(x, x);

Z = -2 * (cos(2*pi*X) + cos(2*pi*Y)) + 2;

Z1 = Z;

Z1(Z1 >= 2) = NaN;

fig = figure;

ax = axes;

hold on;

s1 = surf(ax, X, Y, Z);

s2 = surf(ax, X, Y, Z1);

set(s1, 'LineWidth', 0.5, 'EdgeColor', 'r', 'FaceColor', 'w');

set(s2, 'LineWidth', 0.5, 'EdgeColor', 'b', 'FaceColor', 'w');

camzoom(ax, 0.5);

view(ax, [120,30]);

set(ax, 'Box', 'on', 'PlotBoxAspectRatio', [1, 1, 1.5]);

hold off;

This is the exported PDF-file.

Also I tried to plot the two part of the surface (e.g., f(x, y) <=2 and f(x, y) > 2) separately, But I find the boundaries between the two parts is not connected smoothly. Please see the following codes and the results.

clearvars; clc; close all; fclose all; format short; format compact;

x = linspace(-0.5, 0.5, 21);

[X, Y] = meshgrid(x, x);

Z = -2 * (cos(2*pi*X) + cos(2*pi*Y)) + 2;

Z1 = Z;

Z2 = Z;

Z1(Z1 >= 2) = NaN;

Z2(Z2 < 2) = NaN;

fig = figure;

ax = axes;

hold on;

s1 = surf(ax, X, Y, Z2);

s2 = surf(ax, X, Y, Z1);

set(s1, 'LineWidth', 0.5, 'EdgeColor', 'r', 'FaceColor', 'w');

set(s2, 'LineWidth', 0.5, 'EdgeColor', 'b', 'FaceColor', 'w');

camzoom(ax, 0.5);

view(ax, [120,30]);

set(ax, 'Box', 'on', 'PlotBoxAspectRatio', [1, 1, 1.5]);

hold off;

Best regards,

Qilin.

Answer 1

[AndresVar]

How about just 1 surface but you tweak the colormap

x = linspace(-0.5, 0.5, 21);
[X, Y] = meshgrid(x, x);
Z = -2 * (cos(2*pi*X) + cos(2*pi*Y)) + 2;

% color 
C = Z;
C(Z<=2)=-1;
C(Z>2)=1;

% plot
fig=figure;
ax = axes;
s1 = surf(ax,X,Y,Z,C);

% color
s1.EdgeColor="interp";
s1.FaceColor='w';
s1.LineWidth=0.5;
BlueRedColormap = [0,0,1;1,0,0]; % just red and blue
colormap(fig,BlueRedColormap);

% pretty
view(ax,[120,30]);
set(ax,'Box', 'on', 'PlotBoxAspectRatio', [1, 1, 1.5]);

%saveas(gcf,'RedBlueSurf.pdf');

[qilin guo]

Dear AndresVar, thank you very much! This is what I exactly want. You make it in an elegant way!