How to draw a white circle ?

Hello,

I would like to draw a white circle in a black square in Matlab but I don't have any idea how to do it. Would you please explain me how to do it ?

In advance, thank you !

Answer 1

[Azzi Abdelmalek]

r=4; %radius
x0=0;y0=0; % circle center coordinates
x=x0-r:0.01:x0+r
y=sqrt(r^2-(x-x0).^2)+y0;
fill([x0-r x0+r x0+r x0-r ],[y0-r y0-r y0+r y0+r ],'k')
hold on;
plot(x,y,'w',x,-y,'w');
axis square
axis([x0-2*r x0+2*r y0-2*r y0+2*r]) % facultative

[K BV]

Thank you for your answer.

I could understand that the circle's equation is : y=sqrt(r^2-(x-x0).^2)+y0;

But I didn't understand this line : x=x0-r:0.01:x0+r

Would you please explain why did you write this ?

Thanks again !

[Azzi Abdelmalek]

Yes

fill([x fliplr(x)],[y fliplr(-y)],'w')

[Azzi Abdelmalek]

 x=x0-r:0.01:x0+r

is a vector of points we are using to plot your circle

Answer 2

[Image Analyst]

This is available from the FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_create_a_circle.3F

[K BV]

Thanks for the link ! I'll search in the FAQs the next time before asking any question ;)