Draw line to connect centroids - matlab

Question

I have an image
.
After I process to find centroid, it has four centroids.
My goal is I want to connect them using line and measure the angle between this area. To be clear about the centroid and my goal, you can open .
Here it is my code to achieve the centroid
I = imread('22c.jpg');
Ibw = im2bw(I);
Ibw = imfill(Ibw,'holes');
Ilabel = bwlabel(Ibw);
stat = regionprops(Ilabel,'centroid');
imshow(I); hold on;
for x = 1: numel(stat)
plot(stat(x).Centroid(1),stat(x).Centroid(2),'ro');
end
The problem is I am still confused to do the next (to connect each centroids and measure the angle). I need your help, thanks

Answer 1

Here is a file exchange link to bresenham.m
Changed your code to get all the 4 centroids
%// read your input image
im = imread('http://i.stack.imgur.com/xeqe8.jpg');
BW = im>220;
CC = bwconncomp(BW);
stat = regionprops(CC,'Centroid');
figure; imshow(BW); hold on
for x = 1: numel(stat)
plot(stat(x).Centroid(1),stat(x).Centroid(2),'ro');
end
Here is the output:
Further implementation:
%// putting all the Centroid coordinates into corresponding x,y variable
x = [stat(1).Centroid(1),stat(2).Centroid(1),stat(3).Centroid(1),stat(4).Centroid(1)];
y = [stat(1).Centroid(2),stat(2).Centroid(2),stat(3).Centroid(2),stat(4).Centroid(2)];
%// obtain row and col dim
[r,c] = size(BW);
%// get all x,y values connecting the centroid points
[xAll{1},yAll{1}] = bresenham(x(1),y(1),x(4),y(4));
[xAll{2},yAll{2}] = bresenham(x(2),y(2),x(3),y(3));
[xAll{3},yAll{3}] = bresenham(x(3),y(3),x(4),y(4));
%// change row and col subs to linear index
for ii = 1:3
idx{ii} = sub2ind(size(BW),yAll{ii},xAll{ii});
end
%// change grayscale image to 3D (as you want red line)
out = repmat(im,[1,1,3]);
%// obtaining corresponding index of all 3 slices
for ii = 1:3
idxall{ii} = bsxfun(#plus, idx{ii},[0:2].*(r*c));
end
%// keep only the index of 1st slice to 255 and changing rest to 0 to obtain a red line.
%// Similar process for blue line except keep the index in the 3rd slice to 255
out(cat(1,idxall{:})) = 0;
out(idx{1}) = 255;
out(idx{2}) = 255;
out(idx{3}+2*(r*c)) = 255;
%// see what you have obtained
figure; imshow(out);hold on
for x = 1: numel(stat)
plot(stat(x).Centroid(1),stat(x).Centroid(2),'bo');
end
Result:
Note: The line may look dotted due to the picture's large size, but its continuous
Last figure zoomed to see continuous line:
Going further:
You may have to take the advice of #Spektre to find the angle of inclination using atan2. Also refer his answer for more explanation.