Making circular shapes using equation of circle

Hello,

I am trying to make circular shapes using this code, but it is plotting half circles or quater circles instead.

close all; clear all;

%% Data for Agglomerates
N = 2; % number of circles
a = 1; % lowest diameter of circles
b = 5 ; % highest diameter of circles
Diam = a + (b-a).*rand(N,1);
Diam = round(Diam);

aaa= 0;             % minimum x and y coordyinate limit for circles
bbb= sum(Diam);   % maximum x and y coordinat limit for circles
M=2  ;
Axes= zeros(N,M);
Axes(:,1)=aaa+(bbb-aaa)*rand(N,1);
for k=2:M
    aaa=randperm(N);
    Axes(:,k)=Axes(aaa,1);
end
Axes_Label ={'X axis','Y axis'};
Data_agglo = [Diam Axes];
Data_Label ={'Diameter','X axis','Y axis'};
R = Diam ./2;

%% generate mesh

xmin = min(Data_agglo(:,2)-R);
xmax = max(Data_agglo(:,2)+R);

ymin = min(Data_agglo(:,3)-R);
ymax = max(Data_agglo(:,3)+R);

[Xgrid,Ygrid]= meshgrid(linspace(xmin,xmax,200), linspace(ymin,ymax,200));
plot(Xgrid,Ygrid,'k',Ygrid,Xgrid,'k')
hold all

%% get active dipoles


for i =1:1:size(Data_agglo,1)
    
    active = Xgrid.^2 + Ygrid.^2 <= R(i).^2;
    hold on
    plot(Data_agglo(i,2)+Xgrid(active),Data_agglo(i,3)+Ygrid(active),'o');
    %     plot(Xgrid(active),Ygrid(active),'o','MarkerFaceColor','red');
    hold on
end

the problem is with the active line or with the whole algorithm.Does anyone knows?

Answer 1

[Geoff Hayes]

@hamzah khan - I think the issue is with the bounds for your grid

xmin = min(Data_agglo(:,2)-R);
xmax = max(Data_agglo(:,2)+R);
ymin = min(Data_agglo(:,3)-R);
ymax = max(Data_agglo(:,3)+R);

Once, when running the code, there were no partial or full circles drawn. This was with the following

Diam = [1;4];
Data_agglo = [1.0000    2.4709    2.4709;...
              4.0000    3.8953    3.8953];

creating intervals for x and y as

x : [1.8953 5.8953]
y : [1.8953 5.8953]

and radii of

0.5
2

Given the intervals for x and y, then I don't see how any (x,y) pair would satisfy square of either radius. I think that you need to take into account the centre of the circle when finding the active set of elements in the circle

%% get active dipoles
for i =1:1:size(Data_agglo,1)
    active = ((Xgrid - Data_agglo(i,2)).^2 + (Ygrid - Data_agglo(i,3)).^2) <= R(i).^2;
    hold on
    plot(Xgrid(active),Ygrid(active),'o');
end

[Chris Dan]

Thank you so much :-) your explanation is very good

[Chris Dan]

Hii Geoff Hayes

Do you know how it can be done in 3D? I am making a 3d mesh and using x^2 +y^2+z^2 <= R^2 but I am getting errors in plot3

[Geoff Hayes]

@hamzah khan - I'm not sure how it can be done in 3D (haven't tried to do this before). Can you post the code and the full error message?

[Chris Dan]

Hii Geoff Hayes,

I have done it in 3D, here is my code :

close all; clear all;

%% Data for Agglomerates
N = 15; % number of spheres
a = 1; % lowest diameter of sphere
b = 10 ; % highest diameter of sphere
Diam = a + (b-a).*rand(N,1);
Diam = round(Diam);

aaa= 0;             % minimum center x and y coordinate limit for spheres
bbb= sum(Diam) ;  % maximum center x and y coordinat limit for sphere
% bbb= N*((1+sqrt(5))/2);  % maximum center x and y coordinat limit for sphere
M=3  ;
Axes= zeros(N,M);
Axes(:,1)=aaa+(bbb-aaa)*rand(N,1);
for k=2:M
    aaa=randperm(N);
    Axes(:,k)=Axes(aaa,1);
end
Axes_Label ={'X axis','Y axis','Z axis'};
Data_agglo = [Diam Axes];
Data_Label ={'Diameter','X axis','Y axis','Z axis'};
R = Diam ./2;

%% generate mesh
Nn = 50;
xmin = min(Data_agglo(:,2)-R);
xmax = max(Data_agglo(:,2)+R);

ymin = min(Data_agglo(:,3)-R);
ymax = max(Data_agglo(:,3)+R);

zmin = min(Data_agglo(:,4)-R);
zmax = max(Data_agglo(:,4)+R);

[Xgrid,Ygrid,Zgrid]= ndgrid(linspace(xmin,xmax,Nn), linspace(ymin,ymax,Nn), linspace(zmin,zmax,Nn));

% plot3(Xgrid(:),Ygrid(:), Zgrid(:),'.','MarkerFaceColor','blue');
% hold all
%% get active dipoles
tic

for i =1:1:size(Data_agglo,1)
    active = ((Xgrid - Data_agglo(i,2)).^2 + (Ygrid - Data_agglo(i,3)).^2 + (Zgrid - Data_agglo(i,4)).^2) <= R(i).^2;
%     plot3(Xgrid(active),Ygrid(active),Zgrid(active),'.r');
    plot3(Xgrid(active),Ygrid(active),Zgrid(active),'o','MarkerFaceColor','red');
    hold all
end
axis equal
grid on
toc

The only confusion I have is that for 2D and for 3D I am creating active for each circle in the for loop, would it be possible that i create it for all circles without the loop. One matrix of active which has 1s and 0s for all the circles and than i plot it

Answer 2

[Image Analyst]

I think using the viscircles() function would be much simpler. Would that work for you?

[Chris Dan]

Hii,

no I have to use a grid to find out which points are inside the spheres