Hi Jakub,
I think this does exactly what you're looking for. I've commented the code so it's easy to follow. Note that I've used the intersections entry on the file exchange.
% Make a blob
BW = false(20);
BW(4:16,6:12) = true;
% Get its boundary and a center location
bb = bwboundaries(BW);
bbXY = bb{1}(:,[2 1]);
centXY = mean(bbXY,1);
figure, imagesc(BW), hold on, plot(bbXY(:,1),bbXY(:,2),'g',centXY(1),centXY(2),'yo')
% Make a line that is sure to extend past the object
cutLineXY = [-1 0; 1 0] * sum(size(BW).^2);
% Define how many times we will rotate it
thetas = 0:15:360;
sth = sind(thetas);
cth = cosd(thetas);
for i = 1:length(thetas)
% Rotate the line
R = [cth(i) sth(i); -sth(i) cth(i)];
rotLineXY = cutLineXY * R;
% Shift it to the center
rotLineXY = rotLineXY + [centXY;centXY];
plot(rotLineXY(:,1),rotLineXY(:,2),'k')
% Check where it intersects our boundary
[X,Y] = intersections(rotLineXY(:,1),rotLineXY(:,2),bbXY(:,1),bbXY(:,2));
% Every 2nd intersection will be "inside" the blob
for cutNo = 1:2:length(X)
plot(X(cutNo:cutNo+1), Y(cutNo:cutNo+1),'-w.')
end
end
Does that answer your question?
