How to create a 2D ring placed in 3D matrix, with user defined radius?

I want to create a ring with user defined radius, the ring should be placed in 3D volume and the output should be only one 3D matrix containing the ring.

[KSSV]

Same question:

http://in.mathworks.com/matlabcentral/answers/304855-how-to-create-a-ring-using-meshgrid-with-user-defined-radius

[Israr Ul Haq]

May be here it is more clear, I didn't receive the proper answer in my last question.

[Stephen23]

Duplicate:

http://www.mathworks.com/matlabcentral/answers/304855-how-to-create-a-ring-using-meshgrid-with-user-defined-radius

Answer 1

[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?