Animation in Matlab

http://www.maelabs.ucsd.edu/mae150/mae150_resources/Matlab_Tips/intro_to_kinematic_plotting.htm

%--------------- Introduction to Kinematic Plotting ---------------

%

% MATLAB provides three ways of generating animations:

% 1. Repeatedly execute the 'plot' command in a loop. This is the easiest method

%    but results in a flashing screen.  (see the first example)

%

% 2. Set up a graph using handle graphics, and repeatedly execute the 'drawnow' command.

%    This eliminates the flashing problem. (see the second example)

% 3. Save a number of different pictures and then play them back as a movie. This is useful for very complex figures that would be slow to animate using the prior methods. (see Matlab help)

% Simple (but effective) visualizations can be done with line plots. That is, draw a new line in a new location after a short pause and erase the old line.

% (to plot 3D shapes see the patch command)

% Matlab can help visualize and animate the kinematics of mechanisms and other objects

As you can see, this code allows you to create a simple animation.

%------------ A simple animation using 'plot' and 'drawnow' ------------

% A Simple Animation of a rotation arm

theta_step = 5*pi/180;

r = 1;               % radius of the arm

for theta=0:theta_step:2*pi

% In order to draw a stick figure you need to have a start point and an end point

% (in the case of a closed figure the end point must end at the start point;

% this allows the figure to be completely closed), the following two commands define

% the points of the stick figure:

    data_pt(1,:) = [0 0];                        % first point is the origin

    data_pt(2,:) = [r*cos(theta) r*sin(theta)];  % second point is end of vector

    plot(data_pt(:,1),data_pt(:,2));             % connect the points with a line

    axis([-1.5 1.5 -1.5 1.5]);   % set the axis limit to include the range of animation

    axis manual     % freezes the axis scaling

    pause(0.1)      % puts a delay in seconds (if time is zero, a keyboard hit is required)

end

disp('Hit the Space Bar to Continue');

pause;

%********************* Ways to reduce flashing ***********************

%  Do the animation again while reduce flashing.

%  There are two steps to reduce the flashing on the plot. Please see

%  ‘Introduction to Graphic Handles’ for help on graphic handles.

%  1. define EraseMode in the ‘plot’ command. 

%  2. instead of using ‘plot’ repeatedly, change the data by ‘set’ command.

theta_step = 5*pi/180;

theta = 0:theta_step:2*pi;          % generate and store the angle sequence

x_pt = [0 1];                       % define the end points of the stick figure

y_pt=[0 0];             

axis([-1.5 1.5 -1.5 1.5]);

hold on;

hndl=plot(x_pt,y_pt,'EraseMode','background'); % connect the end points,

                                               % and use "EraseMode" to REDUCE FLASHING

set(gca,'DataAspectRatio',[1 1 1]);            % make x,y-axis relative scaling equal

for j=1:length(theta)

    x_pt=[0  cos(theta(j))];

    y_pt=[0  sin(theta(j))];

    set(hndl,'XData',x_pt,'YData',y_pt);       % REDUCE FLASHING

    drawnow         % forces Matlab to redraw the plot at the current values

    pause(.1)

end

%  Compare this animation with the previous one: 

%  In this case, we generate and store the end points BEFORE we call them in each loop.

%  In the previous one, we generate the end points and draw a new line IN each loop.

%  When the process of generating data is complex and the computational time delay

%  cannot be ignored, we usually do the computation first, then draw the data in each loop

%------------------------------------------------------------

% Key functions:  drawnow, pause(time), set

% Key properties: EraseMode, DataAspectRatio, XData, YData