%--------------- 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
% 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)
disp('Hit the Space Bar to Continue');
%********************* 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
axis([-1.5 1.5 -1.5 1.5]);
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
set(hndl,'XData',x_pt,'YData',y_pt); % REDUCE FLASHING
drawnow % forces Matlab to redraw the plot at the current values
% 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