How to create a ring using meshgrid with user defined radius ?

I want to make a ring using meshgrid with user defined radius. Thanks

Answer 1

[KSSV]

clc; clear all ;
M = 10 ;
N = 100 ;
R1 = 0.5 ; % inner radius 
R2 = 1 ;  % outer radius
nR = linspace(R1,R2,M) ;
nT = linspace(0,2*pi,N) ;
%nT = pi/180*(0:NT:theta) ;
[R, T] = meshgrid(nR,nT) ;
% Convert grid to cartesian coordintes
X = R.*cos(T); 
Y = R.*sin(T);
[m,n]=size(X);
% Plot grid
figure
set(gcf,'color','w') ;
axis equal
axis off
box on
hold on
% Plot internal grid lines
for i=1:m
    plot(X(i,:),Y(i,:),'k','linewidth',1.5); 
end
for j=1:n
    plot(X(:,j),Y(:,j),'k','linewidth',1.5); 
end

You may check the link:

http://in.mathworks.com/matlabcentral/fileexchange/33731-meshing-a-plate-using-four-noded-elements

[Israr Ul Haq]

 Dr. Siva Srinivas Kolukula, Thanks for your answer. Is it possible to get one output variable, which contains the ring ? Because here you are plotting X and Y separately.

[KSSV]

How you can get one output for a 2D problem? As the ring is 2D, you will have two coordinates which specify the location.

[Israr Ul Haq]

I mean, I need one 2D matrix as an image in the output

[KSSV]

You will get 2D matrices for x and y.

[Israr Ul Haq]

Can I get only one 2D matrix ?

[KSSV]

Yes one 2D matrix for x and one 2D matrix for y.

[Israr Ul Haq]

K0 =[0 1] [x,y,z] = meshgrid(-A/2:(A/2)-1,-D/2:(D/2)-1,-B/2:(B/2)-1); out = exp( 1i * (k0(1) * x + k0(2) * y + k0(3)*z));

In this case the output is only one 3D matrix that is "out". I need just one output matrix like this.

"Yes one 2D matrix for x and one 2D matrix for y" it means there are 2 images that is x and y, but I only need one image as a ring. can we combine x and y to make only one matrix ?

[KSSV]

clc; clear all ;
N = 100 ;
R1 = 0.5 ; % inner radius 
R2 = 1 ;  % outer radius 
th = linspace(0,2*pi,N) ;
% inner circle 
x1 = R1*cos(th) ; y1 = R1*sin(th) ;
% Outer circle 
x2 = R2*cos(th) ; y2 = R2*sin(th) ;
% merge both 
x = [x1 NaN  fliplr(x2)] ;
y = [y1 NaN fliplr(y2)] ;
%%Make a mesh 
x0 = min(x) ; x1 = max(x) ;
y0 = min(y) ; y1 = max(y) ;
xx = linspace(x0,x1,N) ;
yy = linspace(y0,y1,N) ;
[X,Y] = meshgrid(xx,yy) ;
%%Get points inside the ring 
D = (X.^2+Y.^2) ;  
D(D<R1) = NaN ;
D(D>R2) = NaN ;
pcolor(D) ;  
shading interp ;

D will be a single matrix. Is it okay?

[Israr Ul Haq]

Thanks it is perfect

[KSSV]

I am curious to know...why you are specific about single output?

[Israr Ul Haq]

I have 3D data and I want to correlate the 2D ring matrix with each slice of 3D data.

Answer 2

[Image Analyst]

See the FAQ for code: http://matlab.wikia.com/wiki/FAQ#How_do_I_create_a_ring.3F