How can I select imagesc boundaries on the y-axis?

Hello,

I would like to plot two imagesc bars displaying temperature over time to compair two years with each other. Since I want to plot some other graph on top of them, I need the "Temperature Bar" to be at a certain location on the y-axis in my plot:

% made up example data
W18_T = [1:10]';
W18_Y = [0 -0.5 -0.75 -0.3 0.1 0.2 0.3 0.4 0.4 0.3]';
W19_T = [11:20]'-10;
W19_Y = [1 0.5 0.25 0 -0.1 -0.2 -0.1 0.2 0.4 0.3]';
SP18_Y = [100 105 106 103 101 102 103 104 104 103]'; SP18_T =  [1:10]';
SP19_Y = [120 125 126 123 121 122 123 124 124 123]'; SP19_T = [11:20]'-10;

% identify plot area on the y-axis
schnittpunkt = min([SP18_Y; SP19_Y])+((max([SP18_Y; SP19_Y])-min([SP18_Y; SP19_Y]))/2)

% plot
figure; hold on;
imagesc(W18_T',[min(SP18_Y) schnittpunkt],W18_Y'); 
imagesc(W19_T',[schnittpunkt max(SP19_Y)],W19_Y'); 
plot(SP18_T,SP18_Y,'LineWidth',2,'Color','k')
plot(SP19_T,SP19_Y,'LineWidth',2,'Color','k')

The problem is that even if I set " [min(SP18_Y) schnittpunkt] " as the "Bouderies" for my imagesc plot, it makes the Display much wider then I want.

I want the first bar to be plottet in the y-axis range of [min(SP18_Y) schnittpunkt] --> [100 113], but imagesc plots it at [87 126] ...

and the secound bar to be plottet in the y-axis range of [schnittpunkt max(SP19_Y)] --> [113 126], but imagesc plots it at [100 139]

How can I correct for it without "guessing" how wide to make the areas? I need to do this for a lot of different Variables at lot of different ranges, so trying by hand is not an option.

Thank you very much!

Answer 1

[Mathieu NOE]

hello Kathy

you needed indeed :

• to reverse the Y direction for imagesc

How can I reverse the y-axis when I use the IMAGE or IMAGESC function to display an image in MATLAB? - MATLAB Answers - MATLAB Central (mathworks.com)

• to create the color matrix ( 3rd argument of imagesc) with as many lines as the difference of y range : like 100 to 133 y range => 13 lines for C color matrix. therefore use of repmat

beside that no major change in your code (removed all unnecessary transpose operators here and there)

% made up example data
W18_T = (1:10);
W18_Y = [0 -0.5 -0.75 -0.3 0.1 0.2 0.3 0.4 0.4 0.3];
W19_T = (11:20)-10;
W19_Y = [1 0.5 0.25 0 -0.1 -0.2 -0.1 0.2 0.4 0.3];
SP18_Y = [100 105 106 103 101 102 103 104 104 103]; SP18_T =  [1:10];
SP19_Y = [120 125 126 123 121 122 123 124 124 123]; SP19_T = [11:20]-10;
% identify plot area on the y-axis
schnittpunkt = min([SP18_Y SP19_Y])+((max([SP18_Y SP19_Y])-min([SP18_Y SP19_Y]))/2);
% plot
figure; hold on;
y = [min(SP18_Y) schnittpunkt];
C = repmat(W18_Y,round(y(2)-y(1)),1);
imagesc(W18_T,y,C); % y range should be 100 - 113
y = [schnittpunkt max(SP19_Y)];
C = repmat(W19_Y,round(y(2)-y(1)),1);
imagesc(W19_T,[schnittpunkt max(SP19_Y)],C);  % y range should be 113 - 126
set(gca,'YDir','normal'); % important tip here ! https://fr.mathworks.com/matlabcentral/answers/94170-how-can-i-reverse-the-y-axis-when-i-use-the-image-or-imagesc-function-to-display-an-image-in-matlab
plot(SP18_T,SP18_Y,'LineWidth',2,'Color','k')
plot(SP19_T,SP19_Y,'LineWidth',2,'Color','k')