Calculate normal 2d vectors of a edge line and its vector angle with respective to y axis
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I am working on extracting features from detected edge as shown in the attached image. I have data set of edge coordinate (x,y). My goal is to determine the normal vector of this edge line and compute the angle with respect to y-axis. So the found angle can be used to rotate the tilted image.
1. Extract edge coordinate (x,y) 2. Determine normal vectors using edge coordinates 3. Compute angle between normal vector and y-axis 4. Rotate the image by angle found at 3.
Any helps or suggestions would be highly appreciated.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/163468/image.jpeg)
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Accepted Answer
Fei Deng
on 1 May 2017
Hello, since you have data set of edge coordinate (x,y), you can:
(1) get the angle between this edge line and x-axis by doing linear fit.
Now you have the information of normal vector at well. The angle between normal vector and y-axis is same as angle between this edge line and x-axis.
(2) To rotate the image by θ, you can rotate every point (vector) by θ, then trigonometry states that the new coordinates (x', y') are
x' = x cos θ − y sin θ
y' = x sin θ + y cos θ
If you do not have data set of edge coordinate (x,y) at the very beginning, and you want to extract them from an image file, assuming that you have computer vision system toolbox, you can try detecting corners. Take a look at this page https://www.mathworks.com/help/vision/object-detectors.html, unfold "detect objects using point features".
2 Comments
DGM
on 25 Jul 2022
@Mehri Mehrnia's comment-as-answer moved here:
how to find normal vector in each edge pixel?
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