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

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qilin guo on 23 Mar 2022
Commented: qilin guo on 23 Mar 2022
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.

AndresVar on 23 Mar 2022
Edited: AndresVar on 23 Mar 2022
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 on 23 Mar 2022
Dear AndresVar, thank you very much! This is what I exactly want. You make it in an elegant way!

R2018a

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