# Surf function with interp: symmetric surface shown assymmetrically

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kandaz on 17 Nov 2018
Commented: kandaz on 18 Nov 2018
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.
##### 2 CommentsShowHide 1 older comment
Bruno Luong on 17 Nov 2018
IMO Parula does not releal defect as clear as JET (which I still prefer in general)

Bruno Luong on 17 Nov 2018
Edited: Bruno Luong on 17 Nov 2018
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 on 18 Nov 2018
Wow thanks a lot Bruno! This saved me from a lot of trouble.
Cheers.

madhan ravi on 17 Nov 2018

R2017b

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