How to get co-ordinates of the detected blobs in a video frame?

This programming code is done in Scilab,very much similar to matlab. I have detected features of vehicles and I need to co-ordinates of them or I need their position.What should I do?

Here is the reference code:-

n = aviopen('F:\Rec_2018-12-21 h18_m7_s29.avi'); //open the video file

for i=1:20

im = avireadframe(n,i);

subplot(3,2,1);

imshow(im); //show the images

title('orginal video image'); //title name

loop = rectangle(im,[80, 40, 50, 40],[255 255 255]); //rectangle fixed loop of white clr drawn

subplot(3,2,2);

imshow(loop); // rectangle drawn on input image

se = imcreatese('rect',3,3);

S_bin = im2bw(sub,imgraythresh(im));

S2 = imopen(S_bin,se);

[S3,nn] = imlabel(im2bw(S2,imgraythresh(im))); //label-binary img //nn-number of blobs

[Area, BB, ctr] = imblobprop(S3); // Find the object features

if nn ==BB then

loop1 = rectangle(im,[80, 40, 50, 40],[255 0 0]); //rectangle fixed loop of white clr drawn - veh detection

subplot(3,2,2)

imshow(loop1); // rectangle drawn on input image

title('vehicle presence:no'); //veh det yes only when small box comes inside big box

else

loop1 = rectangle(im,[80, 40, 50, 40],[255 255 255]); //rectangle fixed loop clr changed to red clr

subplot(3,2,2)

imshow(loop1); // rectangle drawn on input image

title('vehicle presence:yes');

end

end

aviclose();

avicloseall();

Here, blobs are not detected properly.Is it because if the function or the size of structuring element?