How to get color bar for 2-D plot?

I am ploting a number of ellipse in a single plot.First i created the ellipse, then I rotate the ellipse through an angle theta by multiplying with a rotation matrix, then i plot it. I want to give a color bar according to the orientation of the ellipse. Any help will be highly appreciated.

Thank you

for ut=1:length(PMAX1)
    a=PMAX1(ut,1);
    b=PMIN1(ut,1);
    uh=.15;
    xc=5;
    yc=frr(ut,1);
    alpha=the1(ut,1);
    m = 1000;
    x = zeros(m,1);
    y = zeros(m,1);
    theta = linspace(0,2*pi,m);
    for k = 1:m
        x(k) = .2 * cos(theta(k));
        y(k) = uh * sin(theta(k));
    end
    R  = [cos(alpha) -sin(alpha); ...
      sin(alpha)  cos(alpha)];
  rCoords = R*[x' ; y'];   % we use the [] to create a 2xm array
  xr = rCoords(1,:)';      % extract the rotated x coordinates
  yr = rCoords(2,:)';      % extract the rotated y coordinates
  plot(xr+xc,yr+yc,'b')
  hold on
end

Answer 1

[Ayush]

Hey Saneesh,

I understand that you are trying to plot multiple ellipses on a single plot and want to add a color bar that reflects the orientation of each ellipse. This involves using the orientation angle to determine the color of each ellipse, and then displaying a color bar to represent these angles visually.

To achieve this, you can:

1. Normalize the orientation angles to map them to a colormap.
2. Use MATLAB's "colormap" to assign colors to each ellipse based on its orientation.
3. Add a color bar to the plot to indicate the mapping from angles to colors.

% Example data
PMAX1 = rand(10, 1) * 5; % Replace with your data
PMIN1 = rand(10, 1) * 3; % Replace with your data
frr = rand(10, 1) * 10;  % Replace with your data
the1 = linspace(0, 2*pi, 10)'; % Replace with your data

% Prepare the figure
figure;
hold on;
colormap(jet); % Use the jet colormap for color representation

% Get the range of angles for normalization
min_alpha = min(the1);
max_alpha = max(the1);

for ut = 1:length(PMAX1)
    a = PMAX1(ut, 1);
    b = PMIN1(ut, 1);
    uh = .15;
    xc = 5;
    yc = frr(ut, 1);
    alpha = the1(ut, 1);
    m = 1000;
    x = zeros(m, 1);
    y = zeros(m, 1);
    theta = linspace(0, 2*pi, m);
    
    for k = 1:m
        x(k) = .2 * cos(theta(k));
        y(k) = uh * sin(theta(k));
    end
    
    R = [cos(alpha) -sin(alpha); sin(alpha) cos(alpha)];
    rCoords = R * [x'; y'];
    xr = rCoords(1, :)';
    yr = rCoords(2, :)';
    
    % Normalize alpha to a value between 0 and 1
    normalized_alpha = (alpha - min_alpha) / (max_alpha - min_alpha);
    
    % Map the normalized alpha to a color
    color = colormap(jet);
    colorIndex = round(normalized_alpha * (size(color, 1) - 1)) + 1;
    ellipseColor = color(colorIndex, :);
    
    % Plot the ellipse with the assigned color
    plot(xr + xc, yr + yc, 'Color', ellipseColor, 'LineWidth', 1.5);
end

% Add a color bar
colorbar;
caxis([min_alpha max_alpha]); % Set the limits of the color bar to match the angle range
xlabel('X-axis');
ylabel('Y-axis');
title('Ellipses with Orientation-Based Color');
hold off;

Explanation:

• Colormap: The "jet" colormap is used here, but you can choose any colormap you prefer.
• Normalization: The angle is normalized between 0 and 1 to map it to the colormap index.
• Color Mapping: For each ellipse, a color is selected based on its orientation.
• Color Bar: A color bar is added to the plot to indicate the orientation corresponding to the colors.

To learn more about "colormap" and "colorbar" , refer to the following MathWorks documentation:

1. colormap : https://www.mathworks.com/help/matlab/ref/colormap.html
2. colorbar : https://www.mathworks.com/help/matlab/ref/colorbar.html

Hope this helps!

Regards