Setting Zero to a specific color in 3D surface plot

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kenneth
kenneth 2022-8-2
评论： kenneth 2022-8-2
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?

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Walter Roberson
Walter Roberson 2022-8-2
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
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Walter Roberson
Walter Roberson 2022-8-2
Ran in:
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
kenneth 2022-8-2
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.

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