# How to rotate a circle around y axis in matlab?

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Ashkan Rigi am 30 Apr. 2022
Bearbeitet: Image Analyst am 30 Apr. 2022
Hi every body. I have some circles with different radius (r) and I would like to rotate it around y axis. This is my code:
for r=1:10
for teta=1:360
C=[0 0];% center
n=0.01;
theta=0:n*pi/360:2*pi; % the angle
m=r*[cos(theta')+C(1) sin(theta')+C(2)]; % the points of circles
R = [cosd(teta) -sind(teta); sind(teta) cosd(teta)]; % rotation matrix
Ry = [cos(teta) sin(teta); -sin(teta) cos(teta)]
point = m';
Circlepointcloud = Ry*point;
axis equal
set(gca,'Visible','off')
ax = gca;
save_name = sprintf('Circlepointcloud_%02d_%03d',r,teta)
save(save_name,'Circlepointcloud')
Name=['Circle' sprintf('Circlepointcloud_%03d_%03d',r,teta) '.jpg'];
exportgraphics(gca,Name,'Resolution',600);
plot(Circlepointcloud(1,:),Circlepointcloud(2,:),'o','color','black')
end
end
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### Akzeptierte Antwort

Image Analyst am 30 Apr. 2022
Bearbeitet: Image Analyst am 30 Apr. 2022
You need to add drawnow at the bottom of the loop so you can see the progress.
You also need to add the center of the circle to the equation and apply the rotation matrix to the CENTER of the circle, not the circle itself because obviously rotating a cirlce about its center will not show any difference. The center should not be at (0,0) or else you won't see any rotation of course.
See attached demos where I rotated an ellipse.
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