MATLAB: How to use (and display) two different colormaps on the same figure

colormapm_contourm_mapm_pcolorMATLABmultiple colormapspcolorscatter

Hey all,

My issue is that I would like to present a contour style map utilising m_map functions (using m_pcolor with colormap 'jet') that is overlaid with some scattered data (using m_scatter with colormap 'cool'). These two colormaps would then be displayed either side of the plot for reference. To me this seems quite a simple task but I can't seem to get Matlab to do it.

Can anyone help me? I've searched through the online community answers and there seem to be some answers that sound like they are relevant but then turn out not to be.

Thanks, Nick

Best Answer

It depends. Are you trying to put the pcolor in the same axes or in different axes. Starting in R2014b, MATLAB has a separate colormap for each axes, so the second case becomes pretty easy.

If you've got the first case (where they're in the same axes) things aren't as simple. If you've got R2014b or R2015a, then you can create two axes and overlay them. It would look a bit like the following:

%%Create two axes
ax1 = axes;
[x,y,z] = peaks;
surf(ax1,x,y,z)
view(2)
ax2 = axes;
scatter(ax2,randn(1,120),randn(1,120),50,randn(1,120),'filled')
%%Link them together
linkaxes([ax1,ax2])
%%Hide the top axes
ax2.Visible = 'off';
ax2.XTick = [];
ax2.YTick = [];
%%Give each one its own colormap
colormap(ax1,'hot')
colormap(ax2,'cool')
%%Then add colorbars and get everything lined up
set([ax1,ax2],'Position',[.17 .11 .685 .815]);
cb1 = colorbar(ax1,'Position',[.05 .11 .0675 .815]);
cb2 = colorbar(ax2,'Position',[.88 .11 .0675 .815]);

As you can see, the messiest part of that is that you don't get automatic layout with two colorbars. That means that you need to position them yourself.

If you're using an earlier version of MATLAB, then things are a little harder. There are a couple of file exchange utilties for combining two colormaps and then offseting the CData of one of your objects. That's probably the approach you'd have to take.

Related Solutions

MATLAB: Imagesc hide one axis

If you are using R2015b or later (I think it is) then,

ax = gca;
imagesc(YourImage, 'Parent', ax);
ax.YAxis.Visible = 'off';

MATLAB: How do i create a colour quiver plot (colquiver) on top of a pcolor depth map

"How can I ... use 2 colourmaps and have 2 colourbars?"

An axis can have more than 1 colorbar but it cannot have more than 1 colormap. A simple solution is to create a second, invisible axes for the sole purpose of hosting a second colormap while all of your data are plotted on the main, visible axis.

Here's a demo (see inline comments for details). I'm using the quiver function instead of the 3rd party colquiver function you mentioned.

% Add primary axes and assign a colormap for the pcolor data
figure()
ax = axes(); 
ax.Colormap = bone(255); 
hold on
% Plot the pcolor data
[X,Y] = meshgrid(-2:0.2:2);
Z = X .* exp(-X.^2 - Y.^2);
h = pcolor(X,Y,Z);
h.EdgeColor = 'none';
% Add a 2nd invisible axis to host the 2nd colormap and colorbar
% HandleVisibility is set to off to avoid accidentally accessing those axes.
ax2 = axes('Visible','off','HandleVisibility','off'); 
% Define the colormap for the quiver data
cmap = hot(size(Z,1)); 
ax2.Colormap = cmap; 
% Plot the quiver data
[U,V] = gradient(Z,0.2,0.2);
for i = 1:size(Z,1)
    quiver(X(i,:),Y(i,:),U(i,:),V(i,:), .2, 'Color', cmap(i,:), 'LineWidth',2)
end
% Set properties for the main axes
axis equal
xlim([-2,2])
ylim([-2,2])
% Add the two colorbars and position the main axes so that
% both colorbars fit on the right side. 
cb(1) = colorbar(ax); 
axPos = ax.OuterPosition; 
cb(2) = colorbar(ax2); 
% Split the vertical space between the 2 CBs.
cb(2).Position(4) = cb(2).Position(4)*.48;
cb(1).Position(4) = cb(1).Position(4)*.48;
cb(1).Position(2) = sum(cb(2).Position([2,4]))+.04; 
cb(2).Position([1,3]) = cb(1).Position([1,3]); 
ax.OuterPosition = axPos; 
% Set colorbar range
caxis(ax2, [-4,4])
% Label the colorbars
ylabel(cb(1),'pcolor')
ylabel(cb(2),'quiver')

Best Answer

Related Solutions

MATLAB: Imagesc hide one axis

MATLAB: How do i create a colour quiver plot (colquiver) on top of a pcolor depth map

Related Question