How to generate and plot multiple semicircle with fixed endpoints but different radius

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Konstantinos Stamatopoulos
评论： Konstantinos Stamatopoulos 2019-11-13
Hi,
I want to generate a plot with multiple semicircles with fixed endpoints but with different radius...below is the code that I'm using and a figure with the ouput...I want to make the three semicircules to oscillate outwards (like the yellow lines) and inwards (like the red lines) with specific rate...i.e. starting from the first semicircle and moves inwardly to the last one at specific rate (I want to synchronize this motion with some MRI images later on)...I'm still missing the straight line even if I use very high radius...any help would be really appreciated!!!
clc; clear; close all; hold on
%coordinates for semicircle 1
Aa = [11.9; -17.091]; %coordinates of point A
Ba = [13.8; -13.8]; % Same with point B
%coordinates for semicircle 2
Ab = [13.8; -13.8]; %coordinates of point A
Bb = [10; -13.8];
%coordinates for semicircle 3
Ac = [10; -13.8]; %coordinates of point A
Bc = [11.9; -17.091];
Coorda=[Aa Ba];
Coordb=[Ab Bb];
Coordc=[Ac Bc];
Coord=[Coorda,Coordb,Coordc];
F=cell(3,1);
for j=1:3
if j==1
F{j,1}=Coord(:,j:j+1);
elseif j==2
F{j,1}=Coord(:,j+1:j+2);
else
F{j,1}=Coord(:,j+2:j+3);
end
end
for i=1:3
n=0;
for h=1:10
d = norm(F{i,1}(:,1)-F{i,1}(:,2));
R = d/2+n; % Choose R radius >= d/2
C = (F{i,1}(:,2)+F{i,1}(:,1))/2+sqrt(R^2-d^2/4)/d*[0,-1;1,0]*(F{i,1}(:,2)-F{i,1}(:,1)); % Center of circle
a = atan2(F{i,1}(2,1)-C(2),F{i,1}(1,1)-C(1));
b = atan2(F{i,1}(2,2)-C(2),F{i,1}(1,2)-C(1));
b = mod(b-a,2*pi)+a; % Ensure that arc moves counterclockwise
t = linspace(a,b,1000);
x = C(1)+R*cos(t);
y = C(2)+R*sin(t);
plot(x,y,'y-',C(1),C(2),'w*')
axis equal
n=n+0.15;
end
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%for inwards movement
hold on
%coordinates for semicircle 1
Aa = [13.8; -13.8]; %coordinates of point A
Ba = [11.9; -17.091]; % Same with point B
%coordinates for semicircle 2
Ab = [10; -13.8]; %coordinates of point A
Bb = [13.8; -13.8];
%coordinates for semicircle 3
Ac = [11.9; -17.091]; %coordinates of point A
Bc = [10; -13.8];
Coorda=[Aa Ba];
Coordb=[Ab Bb];
Coordc=[Ac Bc];
Coord=[Coorda,Coordb,Coordc];
F=cell(3,1);
for j=1:3
if j==1
F{j,1}=Coord(:,j:j+1);
elseif j==2
F{j,1}=Coord(:,j+1:j+2);
else
F{j,1}=Coord(:,j+2:j+3);
end
end
for i=1:3
n=1.5;
for h=1:10
d = norm(F{i,1}(:,1)-F{i,1}(:,2));
R = d/2+n; % Choose R radius >= d/2
C = (F{i,1}(:,2)+F{i,1}(:,1))/2+sqrt(R^2-d^2/4)/d*[0,-1;1,0]*(F{i,1}(:,2)-F{i,1}(:,1)); % Center of circle
a = atan2(F{i,1}(2,1)-C(2),F{i,1}(1,1)-C(1));
b = atan2(F{i,1}(2,2)-C(2),F{i,1}(1,2)-C(1));
b = mod(b-a,2*pi)+a; % Ensure that arc moves counterclockwise
t = linspace(a,b,1000);
x = C(1)+R*cos(t);
y = C(2)+R*sin(t);
plot(x,y,'r-',C(1),C(2),'w*')
axis equal
n=n+2;
end
end
Plot-semicircles.jpg

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回答（1 个）

Hank
Hank 2019-11-13
Thats a neat looking graphic. I don't really understand what its for though. Why don't you just manually draw in the straight line if you need it, as a line and not a circle.
line(Coorda(1,:),Coorda(2,:),'color','k')
line(Coordb(1,:),Coordb(2,:),'color','k')
line(Coordc(1,:),Coordc(2,:),'color','k')
  2 个评论
Konstantinos Stamatopoulos
Konstantinos Stamatopoulos 2019-11-13
Thanks for your reply. The point is that with the current code there is gap between the last yellow semicircle line and the first red semicircle line. Just drawing a line in between won't solve the issue. Moreover, if I want to generate a video showing the motion of those lines outwards and inwards with specific frequency (like in case of a wave), the current code doesn't help me...so I was looking for an improvement/suggestion.
Thanks

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