Animation

This is an example of how to create animations and animated GIFs in MATLAB®. In this example, we will animate the motion of a double-pendulum. We solve the ordinary differential equation using ode45.

Read about the getframe and imwrite functions in the MATLAB® documentation.

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% Parameters and initial conditions
%   mass, link length, initial angles, simulation time
m = 1;
L = 1;
theta1 = 3*pi/4;
theta2 = 3*pi/8;
t = linspace(0, 10, 200);

% Solving ODE of a double pendulum
[T,Y] = ode45(@(t, x) double_pendulum(t, x, m, L), ...
    t, [theta1, theta2, 0, 0]);

% Calculating joint coordinates for animation purposes
x = [ L*sin(Y(:,1)),  L*sin(Y(:,1))+L*sin(Y(:,2))];
y = [-L*cos(Y(:,1)), -L*cos(Y(:,1))-L*cos(Y(:,2))];

% Convert radians to degrees
ang = Y(:,1:2)*180/pi;

% Set up first frame
figure('Color', 'white');
subplot(2,1,1);
plot(T, ang, 'LineWidth', 2);
hh1(1) = line(T(1), ang(1,1), 'Marker', '.', 'MarkerSize', 20, ...
    'Color', 'b');
hh1(2) = line(T(1), ang(1,2), 'Marker', '.', 'MarkerSize', 20, ...
    'Color', [0 .5 0]);
xlabel('time (sec)'); ylabel('angle (deg)');

subplot(2,1,2);
hh2 = plot([0, x(1,1);x(1,1), x(1,2)], [0, y(1,1);y(1,1), y(1,2)], ...
    '.-', 'MarkerSize', 20, 'LineWidth', 2);
axis equal
axis([-2*L 2*L -2*L 2*L]);
ht = title(sprintf('Time: %0.2f sec', T(1)));

% Get figure size
pos = get(gcf, 'Position');
width = pos(3); height = pos(4);

% Preallocate data (for storing frame data)
mov = zeros(height, width, 1, length(T), 'uint8');

% Loop through by changing XData and YData
for id = 1:length(T)
    % Update graphics data. This is more efficient than recreating plots.
    set(hh1(1), 'XData', T(id)          , 'YData', ang(id, 1));
    set(hh1(2), 'XData', T(id)          , 'YData', ang(id, 2));
    set(hh2(1), 'XData', [0, x(id, 1)]  , 'YData', [0, y(id, 1)]);
    set(hh2(2), 'XData', x(id, :)       , 'YData', y(id, :));
    set(ht, 'String', sprintf('Time: %0.2f sec', T(id)));

    % Get frame as an image
    f = getframe(gcf);

    % Create a colormap for the first frame. For the rest of the frames,
    % use the same colormap
    if id == 1
        [mov(:,:,1,id), map] = rgb2ind(f.cdata, 256, 'nodither');
    else
        mov(:,:,1,id) = rgb2ind(f.cdata, map, 'nodither');
    end
end

% Create animated GIF
imwrite(mov, map, 'animation.gif', 'DelayTime', 0, 'LoopCount', inf);

Animated GIF

Copyright 2012 The MathWorks, Inc.
Published with MATLAB® 7.13