Issue with delete(obj)

Hi, I am trying to create a path with an object that moves but then deletes the previous ones, I thought that using delete(obj) would delete it, but it just continues graphing all points. Anyone knows how I can solve this issue?

Here's the code:

clc; clear; close all;
px = 10;
py = 150;
j = 10;
c = 2;
dt = 0.01;
while j < 300
    ruta = animatedline('Color','r','LineWidth',3,'LineStyle',':');
    Vel = 150 + j;
    V = min(50, Vel);
    alpha = atand(150);
    Vx = V*cosd(alpha);
    Vy = V*sind(alpha);
    px(c) = px(c-1)+Vx*dt;
    py(c) = py(c-1)+Vy*dt;
    j = px(c);
    c = c+1;
    addpoints(ruta,px,py);
    auto = scatter(px,py,50,'filled');
    drawnow;
    delete(auto);
end

Answer 1

[Les Beckham]

Here are some modifications that should get you closer to what you wan't. Note the comments I've added in the code to point out the changes. Note that the animation won't show when run here in Answers, but it does work on the desktop.

The main issue was that you were overwriting the animated line plot with a scatter plot (unless I misunderstood what you were trying to do).

px = 10;
py = 150;
j = 10;
% c = 2; % don't need to index if you are adding one point at a time
dt = 0.01;
figure
ruta = animatedline('Color', 'r', 'LineWidth', 3, 'LineStyle', ':'); % <<< moved outside the loop
xlim([10 15]) % <<< specify axis limits so it doesn't keep resizing
ylim([0 1000])
grid on
while j < 15 % <<< reduced so this would run faster for testing
    Vel = 150 + j;
    V = min(50, Vel);
    alpha = atand(150);
    Vx = V * cosd(alpha);
    Vy = V * sind(alpha);
    px = px + Vx*dt; % you don't need to index if you are adding one point at a time
    py = py + Vy*dt; % you don't need to index if you are adding one point at a time
    j = px;
    % c = c + 1; % you don't need to index if you are adding one point at a time
    addpoints(ruta, px, py);
    % auto = scatter(px, py, 50, 'filled'); % don't overwrite with the scatter plot
    drawnow;
    % delete(auto);
end

[Les Beckham]

Actually, after rereading your question, I think this might be what you wanted. This only shows one point on the plot that moves as the loop progresses (you only see the last point here). Adapt as desired.

px = 10;
py = 150;
j = 10;
dt = 0.01;
figure
ax = axes;
plot(ax, px, py, 'ro')
grid on
l = get(ax, 'Children');
xlim([10 16]) % <<< specify axis limits so it doesn't keep resizing
ylim([0 1000])
while j < 15 % <<< reduced so this would run faster for testing
    Vel = 150 + j;
    V = min(50, Vel);
    alpha = atand(150);
    Vx = V * cosd(alpha);
    Vy = V * sind(alpha);
    px = px + Vx*dt;
    py = py + Vy*dt;
    j = px;
    set(l, 'Xdata', px, 'Ydata', py) % <<< just update the x and y data to replace the previous point
    drawnow;
end

[Valentina]

Thank you for your answer, but which part of the code deletes the previous point, I get that the coordinates update, but I don't get how they are deleted. I'm very new at MatlLab so I don't understand the use of set() here.

[Valentina]

After using the code you provided and adapting it to my data, here is the result, I still can't delete the previous points. Maybe is the problem is in my code, because yours works perfectly.

[Valentina]

I think I forgot to add the indexes that I need for a function I call, but I already solved it, thank you so much for help, really.

[Les Beckham]

You are quite welcome. If your question is answered, please click Accept This Answer for the answer that helped you most. Thanks.

Also, if you are just getting started with Matlab, I would highly recommend that you take a couple of hours to go through the free online tutorial: Matlab Onramp

Note that the set() command replaces the x and y data of the existing "line" in the plot (which is actually just one point), so there is no need to delete anything.

Answer 2

[Steven Lord]

Rather than creating and deleting a scatter plot over and over again, I think either using the comet function (if you have all the data before creating the plot) or updating the XData and YData property of the line created by a call to plot (if you're generating the points incrementally) would do what you want.

x = 0:360;
y = sind(x);
h = plot(NaN, NaN, 'o');
axis([0 360 -1 1]);
hold on
for k = 1:numel(x)
    h.XData = x(k);
    h.YData = y(k);
    pause(1/60) % not too fast, not too slow
end

[Valentina]

Thank you for your answer, I initially used the 'comet' function but I wanted to be able to change the color and size so someone recommended I use the animatedline.