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Say I want to create a line between two points and want to show the line taking every step from the first point to the second point inside my plot. How would I go about creating this? For context, I am working on a robotics assignment that requires me to do this with a bug algorithm. I don't want a solution for the algorithm as it would take the fun out of it. Rather, I am just looking for a simple way of showing every step the line takes to join the two points. I currently have no idea what kind of code that would involve but I heard through the grapevine to use a stepsize.

Thank you in advance for any help!

Adam Danz
on 28 Jan 2020

Edited: Adam Danz
on 3 Aug 2021

If needed, interpolate your data to get more or less data points. Here's an example

xvalues = 1:16;

yvalues = (1:16).^2;

newX = min(xvalues) : 0.01 : max(xvalues);

newY = interp1(xvalues, yvalues, newX);

There are several methods to animate a plot. They all involve updating the plot within a loop, using drawnow. Note that this command updates all existing graphics so if lots of other plots/GUIs/Apps are opened all of them will be updated each time drawnow is called which will add a lot of processing time. To reduce this, remove unneeded graphics prior to animation.

Use pause(n) to slow down the animation by inserting short pauses at the end of each iteration: pause(0.1).

Method 1: use an animation technique

% Create the data

x = linspace(0,10);

y = sin(3*x);

% Set up the axis

clf()

axh = axes();

h = animatedline(axh, 'color','b');

ylim(axh, [-1 1]) % set limits before animation

xlim(axh, [1 10]) % set limits before animation

% Animate

for i = 1:numel(x)

addpoints(h,x(i),y(i));

drawnow

end

Method 2: update line coordinates iteratively

The most efficient approach for this method is to produce the line object with all NaN values and then to update the XData, YData, (and ZData, if needed) within the loop.

% Create the data

x = linspace(0,10);

y = sin(3*x);

% Set up the axis

clf()

axh = axes();

h = plot(axh, nan(size(x)),nan(size(y)),'b-'); % nothing will appear in the plot

ylim(axh, [-1 1]) % set limits before animation

xlim(axh, [1 10]) % set limits before animation

% Animate

for i = 1:numel(x)

h.XData(i) = x(i);

h.YData(i) = y(i);

drawnow

% pause(0.1) %to slow it down

end

Another variation is to set the initial object coordinate to a single (nan,nan) coordinate which may be useful in some cases,

% Create the data

x = linspace(0,10);

y = sin(3*x);

% Set up the axis

clf()

axh = axes();

h = plot(axh, nan, nan, 'b-'); % nothing will appear in the plot

ylim(axh, [-1 1]) % set limits before animation

xlim(axh, [1 10]) % set limits before animation

% Animate

for i = 1:numel(x)

set(h, 'XData', x(1:i), 'YData', y(1:i))

drawnow

% pause(0.1) %to slow it down

end

Another method is to plot independent line segments whose properties can be manipulated independently.

% Create the data

x = linspace(-2*pi,2*pi,300);

y = sin(x);

% Break line into segments

x = x(:); % Force col vectors

y = y(:); % Force col vectors

xseg = [x(1:end-1),x(2:end)];

yseg = [y(1:end-1),y(2:end)];

% Set up animation

clf()

hold on % important

xlim([-8 8])

ylim([-1 1])

segColors = jet(size(xseg,1)); % Choose a colormap

% Animate line

for i = 1:size(xseg,1)

h = plot(xseg(i,:),yseg(i,:),'-','LineWidth',3, 'color',segColors(i,:));

drawnow

end

Method 3: Create a movie

This uses getframe to store an image of each frame within a loop and movie to play it back. Otherwise, it's the same as method 2 above.

% Create the data

x = linspace(0,10);

y = sin(3*x);

% Set up the axis

clf()

axh = axes();

h = plot(axh, nan(size(x)),nan(size(y)),'b-'); % nothing will appear in the plot

ylim(axh, [-1 1]) % set limits before animation

xlim(axh, [1 10]) % set limits before animation

% Animate

n = numel(x);

F(n) = struct('cdata',[],'colormap',[]);

for i = 1:n

h.XData(i) = x(i);

h.YData(i) = y(i);

drawnow

F(i) = getframe;

end

Now play it back twice. Save F to play the movie again without recreating the data and figure.

movie(F,2)

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