% CIRCULARSTRUCT
%
% Function to construct a circular structuring element
% for morphological operations.
%
% function strel = circularstruct(radius)
%
% Note radius can be a floating point value though the resulting
% circle will be a discrete approximation
%
% Peter Kovesi   March 2000

function strel = circularstruct(radius)

if radius < 1
  error('radius must be >= 1');
end

dia = ceil(2*radius);  % Diameter of structuring element

if mod(dia,2) == 0     % If diameter is a odd value
 dia = dia + 1;        % add 1 to generate a `centre pixel'
end

r = fix(dia/2);
[x,y] = meshgrid(-r:r);
rad = sqrt(x.^2 + y.^2);  
strel = rad <= radius;