What is the Colormap for plotting weather radar velocity product with interval?

I need the velocity colormap that woud generate the python image attached.

This code does not work for matlab.

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figure('position',[50 100 1800 800])
pcolor(datenum(time),rng,zh)
datetick('x')
shading flat
set(gca,'color','w','LineWidth',1,'fontweight','bold','fontsize',15);
xlabel('\bf{Time (UTC)}','FontSize',12,'FontWeight','bold','color','k');
ylabel('\bf{Height (km)}','FontSize',12,'FontWeight','bold','color','k');
ylim([0.1 10])
caxis([-6 6])
title(['2021-12-24 ' ...
    'Velocity (m/s)']);
%mean_doppler_velocity
cb = colorbar;
cb.Label.String = 'Velocity (m/s)';
colormap vel

Answer 1

[Voss]

You can take the colors directly from the colorbar in the image, and use them as your colormap:

data = imread('velocity plot.jpg');

cmap = permute(data(288:-1:27,903,:),[1 3 2]);

colormap(cmap)
colorbar();

Or maybe one of the colormaps here (or in another File Exchange submission) is similar enough:

https://www.mathworks.com/matlabcentral/fileexchange/68239-pycolormap4matlab

[Tunde Adubi]

Oh Thanks, but the exact colormap (name) is not in the list as seen in the link you shared. so, I used RdBu_r (a similar one) and didnt get the color. How do I used this (RdBu_r) in the script below.

%% data extraction from NetCDF file     
test_zh1 = ncread(fname,'mean_doppler_velocity');

zh = [zh,test_zh1];

%     off_set = double(ncreadatt(fname,'reflectivity','add_offset'));
%     scale_factor = double(ncreadatt(fname,'reflectivity','scale_factor'));
%     test_zh = (off_set) + scale_factor.*test_zh1;
%     zh = [zh,test_zh];


clear test_time test_zh1

end

figure('position',[50 100 1800 800])
pcolor(datenum(time),rng,zh)
datetick('x')
shading flat
set(gca,'color','w','LineWidth',1,'fontweight','normal','fontsize',10);
xlabel('\bf{Time (UTC)}','FontSize',10,'FontWeight','normal','color','k');
ylabel('\bf{Height (km)}','FontSize',10,'FontWeight','normal','Color','k');
ylim([0.1 10])
caxis([-20 50])
message = sprintf('2021-12-24\nEquivalent velocity Factor');
title(message, 'FontSize', 11,'FontWeight','bold','Color','k');
%mean_doppler_velocity
cb = colorbar;
cb.Label.String = 'Velocity (m/s)';
colormap RdBu_r

[Voss]

My answer shows how to get the exact colormap and apply it. It's read from the image you posted.

[Walter Roberson]

I would suggest unique() by rows, as colorbar are guaranteed to have to have repeated rows if the number of entries in the map is fewer than the number of pixels used to plot the map.

[Voss]

@Tunde Adubi:

@Walter Roberson makes a good point. This will read the colormap colors from the colorbar portion of the image and remove any repeated colors:

% generating the colormap:
data = imread('velocity plot.jpg');
cmap = unique(permute(data(288:-1:27,903,:),[1 3 2]),'rows','stable');

% applying the colormap:
colormap(cmap)
colorbar();

In addition to that, I'll point out that you can save the colormap for your own use later (so you don't have to go through reading this .jpg each time you need this colormap) by storing it in a mat file:

save('blue_white_red.mat','cmap');

And load it later when you want to use it:

S = load('blue_white_red.mat')

S = struct with fields:
    cmap: [262×3 uint8]

and apply it at will:

figure();
pcolor(randn(50));
colormap(S.cmap);
colorbar();