Setting Zero to a specific color in 3D surface plot

I am trying to set the color scale for my data, which blue for the positive, red for the negative, and setting zero as grey color.

I had been using the code now, which seperate the positive and negetive, but not the zero yet.

%data here means the data I imported from the excel sheet. 

y = data(2:end,1) ;
x = data(1,2:end) ;
Z = data(2:end,2:end) ;
surf(x,y,Z)
colormap(hot(2))
shading interp
caxis([-15 15])

I tried to remove the zero by setting zero as NaN, but this affects the result as "interp" is used.

Is it posible to set the zero as as specifc color with this condition?

Answer 1

[Walter Roberson]

y = data(2:end,1) ;
x = data(1,2:end) ;
Z = data(2:end,2:end) ;
C = sign(Z);
warp(x, y, Z, C)
caxis([-1 1])
colormap([1 0 0;0.2 0.2 0.2;0 0 1])

I did not use surf() because surf() extrapolates between vertices, so the color at each face would reflect the average of adjacent nodes, whereas with warp() it should be point by point

[kenneth]

For this solution, the black color is within the range of nearly [-0.2 , 0.2]. Any method to make the black color range to be only for 0?

[Walter Roberson]

The color is based on sign(Z) which is only zero when Z is exactly 0.

[Walter Roberson]

filename = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/1085635/New%20Microsoft%20Excel%20Worksheet.xlsx';
data = readmatrix(filename);

y = data(2:end,1) ;
x = data(1,2:end) ;
Z = data(2:end,2:end) ;
C = sign(Z);
warp(x, y, Z, C)
caxis([-1 1])
colormap([1 0 0;0.4 0.4 0.4;0 0 1])

When I probe that with the data cursor, the gray part is all exactly 0.

[kenneth]

Oh, thanks for the solution, now I understand the concepts. Thanks so much, I had been looking for this solution for the whole day. Really appreciate that.