How place the tick at the mid value of specific color range and uniform color bar across different ranges of data

Hi,

I want to place the tick at the mid value of the specific color range, for example, for red : 0-10, place the tick at 5, for blue color: 11-20 tick at 15 etc...

Also, I want to create uniform color bar across multiple datasets which have different ranges of values.

What I have so far does not work,

variable  = Mis;
m_proj('Equidistant cylindrical','lat',[-85.044 85.044],'lon',[-180 180],'aspect',.2);
m_pcolor(Lon,Lat,variable);
h=colorbar('Ticks',[0,5,10,15, 20],...
           'TickLabels',{'0','5','10','15', '20');
colormap(jet(5));
caxis([0 20])

Any help is appreciated.

Answer 1

[Cris LaPierre]

I'll start a new anwer using a different approach. This time we'll manually define everything - no shortcuts. That should allow you more control over what is going on, making it easier for you to adapt.

Going back to your original question:

• 0-10 = red, tick at 5
• 11-20 = blue, tick at 15
• etc.

First, create a custom colormap, manually specifying the colors and the range they apply to. Note that the ranges aren't equal (one has 5 in it). Not sure why 0-10 is 10 and not 11, but hey, it's working.

% Create custom colormap
cmap = [repmat([1 0 0],10,1)     % >=0 & <=10 (red)
    repmat([0 0 1],10,1)         % >10 & <=20 (blue)
    repmat([0 1 0],10,1)         % >20 & <=30 (green)
    repmat([1 1 0],5,1)];        % >30 & <=35 (yellow)

If you want more colors, add them to cmap. Just adjust the pattern to match the ranges you specify.

With that defined, plot your data. Then set the colormap, caxis limits, and ticks as follows:

colormap(cmap)
h=colorbar;
caxis([0 35])
set(h,'Ticks',[5 15 25 32.5])

Set the ticks to whatever you want to use. It will by default use its value as the label.

If you want the tick label to be different from the tick value, set the tick label property as well. For example, if I wanted the label to display in the middle of the range but show the max value of the range, I'd do this instead:

set(h,'Ticks',[5 15 25 32.5],'TickLabels',num2str([10; 20; 30; 35]))

[nlm]

Thank you so much !

Answer 2

[Cris LaPierre]

Don't have your functions, so here's a quick mockup of how I might do it.

% Use data set included in MATLAB
surf(peaks)
% Create a discrete colormap
cmap=jet(4);
colormap(cmap)
h=colorbar;
% Set tick marks to be middle of each range
dTk = diff(h.Limits)/(2*length(cmap));
set(h,'Ticks',[h.Limits(1)+dTk:2*dTk:h.Limits(2)-dTk])

[nlm]

Thank you. I'm unable to repeat it for different ranges of data.

I have data with different ranges, how can I fix the max and min and mid values.

For example, data 1 : range 0-20

data 2: range 5-35

data 3: range 1-25

I want common color bar 0 -35, with 7 colors with mid values 0, 5, 10, 15, 20, 25, 30.

[Cris LaPierre]

Set your caxis limits:

caxis([0 35])

This line needs to be placed somewhere after the data is plotted yet before the ticks are set to work correctly. Note in this plot the data range is [-10 10] so everything is blue although the colorbar still covers the full range [0 35]. The only other change to the code above is to set cmp equal to 7 colors instead of 4.

[Cris LaPierre]

If it's easier to understand, now that you know the data range, you could simplify setting the Ticks to just

set(h,'Ticks',[2.5:5:35])

[nlm]

I tried this,

cmap=jet(5);

colormap(cmap)

h=colorbar;

h.Limits = [0 30];

dTk = diff(h.Limits)/(2*length(cmap));

set(h,'Ticks',[h.Limits(1)+dTk:2*dTk:h.Limits(2)-dTk])

caxis([0 30])

which resulted in the image attached. How can I keeo five colors and still have multiples of 5, instead of 3.

This set(h,'Ticks',[2.5:5:35]) does not work as with different ranges, the ticks moves away from teh center of the color.

[nlm]

I tried this,

cmap=jet(5);

colormap(cmap)

h=colorbar;

h.Limits = [0 30];

% dTk = diff(h.Limits)/(2*length(cmap));

dTk = 5;

set(h,'Ticks',[h.Limits(1)+dTk:dTk:h.Limits(2)-dTk])

% set(h,'Ticks',[0:5:35])

caxis([0 30])

which resulted in ticks with multiples of 3, is it possible to get multiple of 5. Please find the figures attached.

[Cris LaPierre]

There was a clarification posted above.

"This line needs to be placed somewhere after the data is plotted yet before the ticks are set to work correctly."

[Cris LaPierre]

The step size of your Ticks is directly affected by

1. Your data range
2. The number of colors you include

If you want the step size to be 5 AND want the tick to be centered in the middle of the range, you need to increase the number of unique colors to 6.

Also, you don't need to set h.Limits. Just use caxis.

figure
surf(peaks)
cmap=jet(6);
colormap(cmap)
h=colorbar;
caxis([0 30])
dTk = 5;
set(h,'Ticks',2.5:dTk:30)

[nlm]

They are counts, and have to be whole numbers in step size of 5. I'm unable to make that happen either by num of colors or range.

[nlm]

Hello,

I'm using the following code to plot variable CR with max value = 720. As seen from ranges defined, anything above 720 should be either dark green or dark blue. However, when I plot CR with max 720 value it gives me dark green whereas it should be olive green. Why is that ? What I am missing here ?

variable = CR;
variable(Lat>=60)= NaN;
variable(Lat<=-60)= NaN;
figure(2)
m_proj('Equidistant cylindrical','lat',[-85.044 85.044],'lon',[-180 180],'aspect',.2);
m_pcolor(Lon, Lat,variable);
shading flat;
m_gshhs_h('color','k','linewidth',1.25);
m_grid('linestyle','none','tickdir','in','linewidth',1.5);
cmap = [
    repmat([0.5 0.5 0.5],380,1) % gray 
    repmat([0.3010, 0.7450, 0.9330],100,1)    % light blue  
     repmat([1 0 1],100,1) % magenta
    repmat([0.3940, 0.1840, 0.5560],100,1)    % purple 
    repmat([1 1 0],10,1)         % yellow
    repmat([0.8500, 0.5250, 0.0980],10,1)         % orange
    repmat([0.8 0 0],10,1) % red
    repmat([0.4660 0.6740 0.1880],10,1)   % olive green
    repmat([0 0.45 0],10,1)%  dark green 
    repmat([0 0.2470 0.6410],10,1)];   %(dark blue)
colormap(cmap)
h=colorbar;
caxis([0 740])

[Cris LaPierre]

No idea. I can't run your code. Can you provide the missing pieces?

[nlm]

I attached the data. I tried different ways, but I'm utterly confused as to why when the max value is 720, and color shows dark green instead of olive green.

[Cris LaPierre]

Undefined function or variable 'Lat'.

[nlm]

Can you check now please ?

[Cris LaPierre]

Undefined function or variable 'm_proj'.

I'm probably going to get a similar error for m_pcolor, m_gshhs_h, and m_grid. The last two appear to be handles, but as far as I can tell, there is no command that creates a new plot in the code you've shared. I suspect that must be in your m_proj function?

[nlm]

m_pcolor,m_gshhs_h, m_grid are part of m_map package. My question is why when the max of CR variable is at the threshold of colors it falls into another category. For example, when it is 720 it should be colored olive green but it colors dark green, whereas when it is 718 it colors olive green and when it is 722 it colors dark green as expected. What happens at the thresholds ?

variable = CR;
variable(Lat>=60)= NaN;
variable(Lat<=-60)= NaN;
figure(2)
m_proj('Equidistant cylindrical','lat',[-85.044 85.044],'lon',[-180 180],'aspect',.2);
m_pcolor(Lon, Lat,variable);
shading flat;
m_gshhs_h('color','k','linewidth',1.25);
m_grid('linestyle','none','tickdir','in','linewidth',1.5);
cmap = [
    repmat([0.5 0.5 0.5],380,1) % gray  
    repmat([0.3010, 0.7450, 0.9330],100,1)    % light blue  
     repmat([1 0 1],100,1) % magenta
    repmat([0.3940, 0.1840, 0.5560],100,1)    % purple 
    repmat([1 1 0],10,1)         % yellow
    repmat([0.8500, 0.5250, 0.0980],10,1)         % orange
    repmat([0.8 0 0],10,1) % red
    repmat([0.4660 0.6740 0.1880],10,1)   % olive green
    repmat([0 0.45 0],10,1)%  dark green 
    repmat([0 0.2470 0.6410],10,1)];   %(dark blue)
colormap(cmap)
h=colorbar;
caxis([0 740])

[Cris LaPierre]

I understand your question. I am not able to duplicate the behavior using data I create. Since I can't run your code, I can't tell you why you aren't seeing the behavior you expect.

Inspect this code. You'll see the transition from olive to dark green happens at 720.

x=715:.25:725;
X = meshgrid(x);
surf(X)
cmap = [
    repmat([0.5 0.5 0.5],380,1) % gray 
    repmat([0.3010, 0.7450, 0.9330],100,1)    % light blue  
     repmat([1 0 1],100,1) % magenta
    repmat([0.3940, 0.1840, 0.5560],100,1)    % purple 
    repmat([1 1 0],10,1)         % yellow
    repmat([0.8500, 0.5250, 0.0980],10,1)         % orange
    repmat([0.8 0 0],10,1) % red
    repmat([0.4660 0.6740 0.1880],10,1)   % olive green
    repmat([0 0.45 0],10,1)%  dark green 
    repmat([0 0.2470 0.6410],10,1)];   %(dark blue)
colormap(cmap)
h=colorbar;
caxis([0 740])

[nlm]

Yes, I see it. I'm not sure why it is happening in my code then. The cmap created is the same in my code and yours.