animate plot / trajectory in matlab / octave

Question

I'm trying to animate this spiral using matlab / octave I want it to spiral up or down

t = 0:0.1:10*pi;
r = linspace (0, 1, numel (t));
z = linspace (0, 1, numel (t));
plot3 (r.*sin(t), r.*cos(t), z);

I tried using a for loop to animate it but that just gives me a cone shape see code and image below

clear all, clc,clf,tic
t = 0:0.1:10*pi;
r = linspace (0, 1, numel (t));
z = linspace (0, 1, numel (t));

for ii=1:length(r)
    ii
    plot3 (r.*sin(t(ii)), r.*cos(t(ii)), z);
    hold on
    %pause (.00001)
end

Image

Solution 1

The following appears to work in Octave 3.6.2

t = 0:0.1:10*pi;
r = linspace (0, 1, numel (t));
z = linspace (0, 1, numel (t));

figure
axis([-1 1 -1 1 0 1])
hold on

for ii=1:length(r)
    plot3 (r(ii)*sin(t(ii)), r(ii)*cos(t(ii)), z(ii),'*');
    pause (.001)
end

Solution 2

You could also use the comet3() package, which animates the trajectory through the plot:

delay = 0.001  % seconds
figure
comet3(r.*sin(t), r.*cos(t), z, delay);

This animates a continuous trajectory which I prefer over a discrete sequence of *'s.

The one downside is that the version of comet and comet3 that shipped with Octave 3.6.4 are slow, regardless of the delay you use. But this can be overcome by using the following trick courtesy of andyras in this SO question:

% plot the first point to get started
h = plot3(x(1),y(1),z(1),"b");
axis([min(x), max(x), min(y), max(y), min(z), max(z)]);

% refresh the plot in a loop through the rest of the data
for k = 1:length(z);
   set(h, 'XData', x(1:k));
   set(h, 'YData', y(1:k));
   set(h, 'ZData', z(1:k));
   pause (0.001); % delay in seconds
       % alternatively could provide a velocity function
       % pause(sqrt(vx(k)^2+vy(k)^2+vz(k)^2));  
endfor

Minor note: once you've modified the function, you'll need to force Octave to reload it as it won't do this by default. You can either restart, or better yet use clear comet and clear comet3. Then the next time those functions are called, their definitions will be refreshed.

Solution 3

Certainly not the prettiest, but these are the first changes you need to make to your code for it to do something close to what you want.

t = 0:0.1:10*pi;
z = linspace (1, 0, numel (t));
for ii=1:length(t)
    plot3 (z(ii)*sin(t(ii)),z(ii)*cos(t(ii)), z(ii));
    hold on
    pause (.00001)
end

Comments

[Rick T]

Davin This just gives me an error "line 0: All edges undefined or out of range, thus no plot."

[davin]

@RickT, never used octave before, I'm executing it on Matlab, presumably it's a compatibility/version issue then. You can try adding the clear ... line, or replacing plot3 with scatter3, maybe that will help. If not, I'm fresh out of ideas.

[Assad Ebrahim]

This is nice, though it does not provide a trajectory, only a sequence of points. See stackoverflow.com/a/17773313/181638 for a solution that animates a trajectory.