How to create a filled circle?

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Thomas Nell
Thomas Nell on 28 Dec 2018
Commented: Rik on 2 Oct 2021
Hey guys,
I have this function here for drawing circles:
function circles = circle(x,y,r)
hold on
th = 0:pi/50:2*pi;
x_circle = r * cos(th) + x;
y_circle = r * sin(th) + y;
circles = plot(x_circle, y_circle);
hold off
this, however, only draws line circles. What I want to do is draw a filled circle. How do I go about doing this?
Thanks so much!

Answers (2)

Star Strider
Star Strider on 28 Dec 2018
One option is to use the fill (link) function:
function circles = circle(x,y,r,c)
hold on
th = 0:pi/50:2*pi;
x_circle = r * cos(th) + x;
y_circle = r * sin(th) + y;
circles = plot(x_circle, y_circle);
fill(x_circle, y_circle, c)
hold off
axis equal
end
circleout = circle(3, 4, 2, 'g') % Call ‘circle’ To Create Green Circle
I added a color argument ‘c’ at the end of your current argument list.

Nakarin Ratsuntia
Nakarin Ratsuntia on 2 Oct 2021
Edited: Nakarin Ratsuntia on 2 Oct 2021
This's some simple way to create filled circle with circle equation.
paper = zeros(360,360); %create empty array
[y x] = size(paper); %define y,x as size of array
r = 40; %define radius of a circle
for i=1:y
for j=1:x
if ((i-y/2)^2)+((j-x/2)^2)<(r^2); %define origin is at the center
paper(i,j) = 1; %define array inside the circle eq. = 1
end
end
end
imshow(paper); %show image
  1 Comment
Rik
Rik on 2 Oct 2021
Why the double loop? You can also do this with an array operation:
%define radius and center coordinates
r=20;x_c=0;y_c=0;
%generate a coordinate grid
[y,x]=ndgrid(-20:20,-50:50);
%perform calculation
paper= (x-x_c).^2+(y-y_c).^2 <= r^2;
%show result
imshow(paper)

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