How to match colorbar and countourf plot manually?

clear all;
close all;
x=1:10;x=double(x)

x = 1×10

1 2 3 4 5 6 7 8 9 10

y=x';y=double(y)

y = 10×1

1 2 3 4 5 6 7 8 9 10

z=repmat(x,10,1)

z = 10×10

1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10

maxColorLimit=12

maxColorLimit = 12

minColorLimit=0

minColorLimit = 0

l=maxColorLimit:-1:minColorLimit

l = 1×13

12 11 10 9 8 7 6 5 4 3 2 1 0

npoints=floor(length(l))

npoints = 13

levels=linspace(maxColorLimit,minColorLimit,npoints)

levels = 1×13

12 11 10 9 8 7 6 5 4 3 2 1 0

s1=contourf(x,y,z,levels)

s1 = 2×99

2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 10 10 9 8 7 6 5 4 3 2 1 10 10 9 8 7 6 5 4 3 2 1 10 10 9 8 7 6 5 4

c1=colorbar

c1 = 
  ColorBar with properties:

    Location: 'eastoutside'
      Limits: [1 10]
    FontSize: 9
    Position: [0.8302 0.1109 0.0381 0.8152]
       Units: 'normalized'

  Show all properties

colormap(c1,'Parula(11)')
c1.Ticks=flip(maxColorLimit:-1:minColorLimit); 

I want color barto match exactly with the countour plot. I want colorbar and plot to look like below. In short 0 to 1, 10 to 12 colorbar colors also should be out of it. What am i doing wring here?

Answer 1

[DGM]

Set your caxis()/clim() values. Set your colormap length according to the number of discrete levels you actually have.

x = 1:10;
y = x';
z = repmat(x,10,1);

% this only sets the mapping and colorbar
colorbarrange = [0 12]; % assumed to be integer values
levels = colorbarrange(1):colorbarrange(2);
maplength = diff(colorbarrange);

% plot things
s1 = contourf(x,y,z,levels);
c1 = colorbar;
colormap(parula(maplength))
caxis(colorbarrange)

% if you really want to make sure every tick is labeled
xticks(gca,ceil(min(x(:))):floor(max(x(:))));
c1.Ticks = levels;

[Ankitkumar Patel]

Thank you for the answer. It worked. You can also use clim in sted of caxis as well.

[Ankitkumar Patel]

I also asked one more question: Kind of next step of this one

Check it here: https://de.mathworks.com/matlabcentral/answers/1992888-only-one-colorbar-for-subplots-while-plotting-in-a-for-loop

[DGM]

I write around caxis, since I still run R2019b; clim() wasn't an option until R2022a.

Answer 2

[Angelo Yeo]

The contourf shows the isolevel of the height z and tries to fill the gaps between contour lines. Same color means the same height. Please take a look at the following visualization.

x=1:10;
y=x';
z=repmat(x,10,1);
ax = gca;
[M, c] = contourf(x,y,z, "ShowText", true);
c1=colorbar;
colormap(parula)

As you can see the rightmost color strip tries to fill the place where the value is assumed to be "9". In order to get what you want, I think you can use imagesc.

imagesc(x, y, z);
c1=colorbar;
colormap(parula)

Note how x and y ticks are different from each other.

[Ankitkumar Patel]

Thank you for your answer but want to do it opposite of it. I want colorbar as shown from 1 to 12 in which colorscale for 1 to 10 should match with colorplot.

[Angelo Yeo]

Okay. I explained why you get unexpected behavior. Then you can try this to work around your issue. But note that this is not a robut solution for your problem.

x=1:10;
y=x';
z=repmat(x,10,1);
ax = gca;
[M, c] = contourf(x,y,z);
c1=colorbar;
colormap(c1,'Parula(11)')
c1.Ticks = linspace(1, 10, 12);
c1.TickLabels = string(1:12);