Describe a colormap in the legend of a plot

I am plotting a spacecraft trajectory and use a colormap to visualize the acceleration Vector of the spacecraft in the first part of the trajectory.

The code looks like follow:

%setting color map for Acceleration Vector
    Acc_min = floor(min(ab(ab>0))*10000000);
    Acc_max = ceil(max(ab(ab>0))*10000000);

    Acc_min = min(Acc_min,[],'all');
    Acc_max = max(Acc_max,[],'all');

    Delta_Acc = Acc_max - Acc_min;
    Acc_vals = ceil(Delta_Acc);
    cmap = colormap(jet(Acc_vals)); % colormap should be 'parula' or 'jet'
    colval = round(abs(nor)*10000000-Acc_min); % number of different temperature color values

    for i=1:nval
        if colval(i) < 1
            colval(i) = 1;
        elseif colval(i) > Acc_vals
            colval(i) = Acc_vals;
        end
    end

   % plot accelearation vector
    for i=1:2:nval-1

        Acc_col = cmap(colval(i),:);
        quiver3(pos(i,1),pos(i,2),pos(i,3),arrowlength*Acc(i,1),arrowlength*Acc(i,2),arrowlength*Acc(i,3),'Color', Acc_col)
    end

Now I would like to describe the color map in the legend of the of the plot. I imagine a bar with the same color range and underneath, the actual acceleration values, for example 0.2 m/s^2 on the red end and 0.05 m/s^2 on the blue end. This is just an idea and any other recommendations how to properly label this are welcome!

Any help would be much appreciated!

[Markus Reichel]

I found a way but the labeling is not working properly.

I use this code:

% Color bar
colbar1 = colorbar();
Acc_mean = Acc_min+Delta_Acc/2;
colbar1.Ticks = [0 0.5 1];
colbar1.TickLabels = {append(num2str(Acc_min/10000000),' m/s^2'), append(num2str(Acc_mean/10000000),' m/s^2'),...
    append(num2str(Acc_max/10000000),' m/s^2')};
colbar1.Label.String = 'Acceleration'; colbar1.Label.FontSize = 20; colbar1.Label.HorizontalAlignment = 'left'; colbar1.Label.Position = [2.5 0.05 0];

But the labeling for the upper, red end, the lower, blue end, as well as the colorbar label is not displayed.

[Walter Roberson]

Are those Ticks values within the current caxis()?

[Markus Reichel]

Don´t the Ticks just set the position for the TicksLabels? I want a TicksLabel on the red end, the middle where currently the value is displayed, and on the blue end. Not only in the middle like its´s currently displayed.

Also I found the problem with the labeling for the color bar.

colbar1.Label.String = 'Acceleration'; colbar1.Label.FontSize = 20; colbar1.Label.VerticalAlignment = 'top';

Now the label is on the right side of the bar. I tried using VerticalAlignment = 'bottom' but it will still display the label on the right hand side. Is there a way to show it on the left side of the color bar?

[Markus Reichel]

You were right. the Ticks values were not within the caxis.

With these values it´s working but I don´t know why:

 colbar1.Ticks = linspace(-0.0061, 0.0061, 3) ;

Do you know how I can shift the label of the colorbar from the right to the left?

And thank you very much for your help!

Answer 1

[Voss]

values = 1000*rand(10);
surface(1:10,1:10,values,'FaceColor','interp')
box on
grid on
view(3);

min_max = [min(values(:)) max(values(:))];
cmap = get(gca(),'Colormap');
n_colors = size(cmap,1);
legend_ax = axes(gcf(), ...
    'Units','normalized', ...
    'Position',[0.69 0.89 0.3 0.1], ...
    'Box','on', ...
    'Layer','top', ...
    'XTick',[], ...
    'YTick',[], ...
    'XLim',[0 1], ...
    'YLim',[0 2], ...
    'YDir','reverse');
surface(legend_ax, ...
    linspace(0,1,n_colors+1), ...
    [0 1], ...
    [0:n_colors; 0:n_colors], ...
    'EdgeColor','none');
t = [ ...
    text(legend_ax,[0 1],[1 1],sprintfc('%.2f',min_max)); ...
    text(legend_ax,0.5,1,'m/s^2') ...
    ];
set(t(1),'HorizontalAlignment','left');
set(t(2),'HorizontalAlignment','right');
set(t(3),'HorizontalAlignment','center');
set(t,'VerticalAlignment','top');

[Markus Reichel]

Amazing! Thank you!!

[Voss]

You're welcome!

Answer 2

[John D'Errico]

Hard to put it into a legend, since legend is not designed to do that. Far easier (one line of code) to just put a title above the plot. Have it say something like "red = x (m/s^2) , blue = y (m/s^2)", where x and y are numbers of your choosing. Why make extra work for yourself when there is no gain?

[Markus Reichel]

I would like to visualize this information for better interpretation. I now use colorbar() but have some problems with the labeling.

But thanks for the input!