Surf function with interp: symmetric surface shown assymmetrically

Hello All,

I have a surface Z formed by the following commands (very simplified version) and it is symmetric in XY plane (looking from the top or bottom). However when I use the "surf" command with 'interp', I get a slightly assymetric surface.

clc
clear all

Z=[0 0.1 0.3 0.1 0;
   0 0.2198 0.4432532 0.2198 0;
   0 0.4242 0.7898989 0.4242 0;
   0 0.2198 0.4432532 0.2198 0;
   0 0.1 0.3 0.1 0];
[X,Y] = meshgrid(0:1.5:6,0:1.5:6);

surf(X, Y, Z, 'LineStyle', '-', 'FaceColor', 'interp')
daspect([1,1,0.2])
colormap(jet)
colorbar

When I use decimal numbers instead of the Z values above though, I do not get such a problem.

Any ideas how to obtain the symmetric surface at XY plane?

Cheers.

[Stephen23]

Ugh, jet colormap:

https://blogs.mathworks.com/headlines/2018/10/10/a-dangerous-rainbow-why-colormaps-matter/

https://blogs.mathworks.com/steve/2014/10/13/a-new-colormap-for-matlab-part-1-introduction

https://blogs.mathworks.com/steve/2014/10/20/a-new-colormap-for-matlab-part-2-troubles-with-rainbows/

[Bruno Luong]

IMO Parula does not releal defect as clear as JET (which I still prefer in general)

Answer 1

[Bruno Luong]

The color interpolation carried out by MATLAB is not symetric by values but also by order. This induces the defect.

To trick MATLAB you have te reorganize the data

Z=[0 0.1 0.3 0.1 0;
   0 0.2198 0.4432532 0.2198 0;
   0 0.4242 0.7898989 0.4242 0;
   0 0.2198 0.4432532 0.2198 0;
   0 0.1 0.3 0.1 0];

[X,Y] = meshgrid(0:1.5:6,0:1.5:6);

x = linspace(-1,1,size(Z,2));
y = linspace(-1,1,size(Z,1));

close all
hold on

for k=1:4
    if k<=2
        ix = find(x>=0);
    else
        ix = flip(find(x<=0));
    end
    if mod(k,2)==0
        iy = find(y>=0);
    else
        iy = flip(find(y<=0));
    end   
    surf(X(iy,ix), Y(iy,ix), Z(iy,ix), 'LineStyle', '-', 'FaceColor', 'interp')
end

daspect([1,1,0.2])
colormap(jet)
colorbar

Defect coloring when using single SURF command

[kandaz]

Wow thanks a lot Bruno! This saved me from a lot of trouble.

Cheers.

Answer 2

[madhan ravi]

https://www.mathworks.com/matlabcentral/answers/97324-how-do-i-interpolate-and-plot-3-d-surfaces-in-matlab#answer_106673