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Best way of drawing multiple circles and updating their position

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Raldi
Raldi on 12 May 2018
Answered: Walter Roberson on 12 May 2018
What is the best way to draw a variable number of circles in a plot and update their position?
I have tried
F = rectangle('Position', [(Xpositions - radius) ...
(Ypositions - radius) radius*2 radius*2], ...
'Curvature', [1, 1], 'LineStyle', '--', ...
'EdgeColor', 'r', 'LineWidth', 3);
but since I have multiple circles I would have to create a for loop to draw each circle.
F = viscircles([Xpositions, Ypositions], ...
radii, 'LineStyle', '--', 'EdgeColor', 'r', 'LineWidth', 3);
seems to work fine and draw the circles, but it does not provide of a way to update the positions of the circles.

Accepted Answer

Ameer Hamza
Ameer Hamza on 12 May 2018
Edited: Ameer Hamza on 12 May 2018
The easiest is to use rectangle() and use handle F to update the Position property
F.Position = [x y r r]; % specify a new psition
F.Position = [x_ y_ r_ r_]; % specify a new psition
everytime you update Position property, the figure will be updated with the new position.
In older MATLAB version use
set(F, 'Position', [x y r r])
In case of for loop, create an array of handles,
% inside for loop
F(i) = rectangle('Position', [(Xpositions - radius) ...
(Ypositions - radius) radius*2 radius*2], ...
'Curvature', [1, 1], 'LineStyle', '--', ...
'EdgeColor', 'r', 'LineWidth', 3);
and then set the property using F(1), F(2), ... instead of F to change a particular circle.

  3 Comments

Raldi
Raldi on 12 May 2018
Yes I have already tried using rectangle() as stated in my question, but in order to draw multiple circles I would have to make multiple draw calls with a for loop if I am not mistaken.
Raldi
Raldi on 12 May 2018
So there is no way of skipping the for loop? I will keep doing some tests in case I figure something out and let you know, thanks.
Ameer Hamza
Ameer Hamza on 12 May 2018
Yes, you will need to use for loops. rectangle is a separate graphics object and a call to rectangle() can only create one rectangle. So to draw multiple, a for loop is necessary.
An alternate will be arrayfun, but that is also a fancy way of writing for loop. And in this particular case will not result in any speedup because the actual time-consuming task in your case is the creation of graphics object itself.

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More Answers (2)

Image Analyst
Image Analyst on 12 May 2018
The easiest way is to use viscircles() in the Image Processing Toolbox.

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Walter Roberson
Walter Roberson on 12 May 2018
You need a loop or arrayfun() to create multiple rectangle. But once you have those, you can unpdate the positions more compactly.
v = [rectangle('Position', [1 2 1 1]); rectangle('Position', [4 3 2 2])]; %create vector of them somehow
newpos = num2cell(horzcat(v.Position)*2,2); %calculate new positions
[v.Position] = deal(newpos{:}); %and... action

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