# How to draw a line perpendicular to the medial axis in each point and save the intensity values?

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Hamed Lamei Ramnadi on 23 Oct 2014
Thats what I wrote to get the medial axis (skeleton). im=imread('gray.tif'); skelImg = bwmorph(im, 'skel', inf); figure; imshow(skelImg); hold on; ##### 2 CommentsShowHide 1 older comment
Hamed Lamei Ramnadi on 28 Oct 2014
sure

Bruno Pop-Stefanov on 24 Oct 2014
Take a look at the file overlayLines.m that I have attached. This function draws red lines over an RGB image. You can certainly modify it for a one-channel image. Also, if you examine the loop you'll see how to find the pixel values that the line crosses.
Example:
x = [10,200;50,60];
y = [140,160;20,200];
J = overlayLines(I,x,y);
imshow(J) Hamed Lamei Ramnadi on 28 Oct 2014
Hi Bruno Thank you for your respond but it did not work out actually. Perhaps you did not get my point. I can draw lines by giving x and y. I need a code to draw these lines PERPENDICULAR to the medial axis in each point.
Cheers

Hi, i have solved same issue. my propasal is this (not the best and quickest solution ever but it works):
1. Calculate angle of the line
if true
% code
Xdiff=X-Gpoint2X-GpointX;
Ydiff=Gpoint2Y-GpointY;
angle=tan(Ydiff/Xdiff);
end
Where Gpoint and Gpoint2 are two points on the line and GpointX is point G X coord
2. do
if true
angle=angle*(-1);
% code
end
to make PERPENDICULAR line
3. use
if true
function [Line LineIndexes]=ComputeLineCoords(angle,GpointX,GpointY, shift,L)
X=size(L,2)
StepElevation=tan(angle)*1
Line(1:X)=round(StepElevation*(1:X)- GpointX*StepElevation +GpointY+shift);
OutOfboundsFromS=min(find(Line(1:X)<1))-1;
OutOfboundsFromE=min(find(Line(1:X)>size(L,2)))+1;
if (OutOfboundsFromS==1)
LineIndexes=[OutOfboundsFromS];
else
if (OutOfboundsFromE==size(L,2))
LineIndexes=[OutOfboundsFromE];
else
LineIndexes=;
end
end
OutOfboundsToS=max(find(Line(1:X)>size(L,2)));
OutOfboundsToE=min(find(Line(1:X)<1))-1;
if (Line(OutOfboundsToE)<=1)
LineIndexes=[LineIndexes OutOfboundsToE];
else
if (OutOfboundsToS>=X)
LineIndexes=[LineIndexes OutOfboundsToS];
else
LineIndexes=[LineIndexes X];
end
end
end
To get indexes of pixels in which the line is going (Line) and its bounding box in LineIndexes .
intputs are angle GpointX - Since i wrote it for XY you have to use Y coord of the point where the line should be placed GpointY - Since i wrote it for XY you have to use X coord of the point where the line should be placed shift - 0 should be fine but you hav eto experiment with it a little L - image to get sizes
you might play around a little with the dimensions but this worked for me