# Best way of drawing multiple circles and updating their position

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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) ...
'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.
KALYAN ACHARJYA on 12 May 2018
Are you looking for co-centric circles?
Raldi on 12 May 2018
No in fact they have different positions in the plot

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) ...
'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 CommentsShow 1 older commentHide 1 older comment
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 on 12 May 2018
Edited: 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.

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

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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