Animate trajectory using Octave

Question

I have a set of (x,y) coordinates that describe the trajectory of an object. I'd like to animate this trajectory using GNU Octave.

The data set is quite large so I won't be able to redraw the entire plot at every iteration if I want the animation to be smooth. What functions are there that would allow me to "update" a plot rather than redraw it?

Also, I have another set of (vx,vy) points, which describe the speed of the object. I'd like my animated trajectory to take speed into account. What function should I use to have the program sleep for a couple of milliseconds as to make the trajectory animate at the same speed as the object?

(I already know Octave has functions such as comet, but I need to write my own animator.)

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Edit: Here's what I have up until now. I expected this to run too fast and require me to use pause, but it's still pretty slow (x and y have 10001 elements).

bounds = [min(x) max(x) min(y) max(y)];
axis(bounds);

hold on
for k = 2 : length(x)
    plot(x(k-1:k), y(k-1:k));
    drawnow("expose");
end
hold off

Answer 1

You can use the set command to change just the XData and YData data for a certain plot object h:

h = plot(my_xdata(0),my_ydata(0))
for i_=1:length(my_xdata)
    set(h, 'YData', my_ydata(i_))
    set(h, 'XData', my_xdata(i_))
    pause(sqrt(vx(i_)^2+vy(i_)^2))
end

The pause(x) command pauses for x seconds, which can be less than 1.

Answer 2

I think you are looking for the "hold" command. holding the plot keeps all previous data on the plot and the new data is added on top.