How to calculate the rotation of this egg?

Question

Ashfaq Ahmed 2022-8-9

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https://ww2.mathworks.cn/matlabcentral/answers/1776600-how-to-calculate-the-rotation-of-this-egg

评论： Matt J 2022-8-9

Hi all!

Suppose I have this egg in figure1, standing still. But when it rotates a bit in figure 2, how can I calculate the rotation angle using MATLAB coding? Can anyone please give an idea on it?

I have attached the images in the question. (egg1, and egg2). Any suggestion from you will be much appreciated ^_^

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Answer 1

John D'Errico 2022-8-9

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Find a bounding box, where the box can be rotated, not a box that is aligned with the axes.
Find the orientation (angle of inclination) of the long sides of the bounding box. atan2 will help you there.
Nothing more needed, since atan2 did all the work.

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Ashfaq Ahmed 2022-8-9

Hi! Thank you for your reply. How can I find a bounding box? I don't understand it when you say, "where the box can be rotated, not a box that is aligned with the axes". Can you please explain?

John D'Errico 2022-8-9

编辑：John D'Errico 2022-8-9

在 MATLAB Online 中打开

egg2.png

I'm sure the Image processing toolbox has a bounding box utility. (I'll find it in a minute or so, and post the link too.) But you can also extract the points as a set of pixel locations, and then use my minboundrect utility.

https://www.mathworks.com/matlabcentral/fileexchange/34767-a-suite-of-minimal-bounding-objects?s_tid=srchtitle

Ok. A quick search tells me the tool is regionprops. It looks like you need to do something like:

regionprops(egg2,'boundingbox')

Lacking the IPT, I've never used it, but one of those tools will get you there.

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Answer 2

Matt J 2022-8-9

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https://ww2.mathworks.cn/matlabcentral/answers/1776600-how-to-calculate-the-rotation-of-this-egg#answer_1023915

编辑：Matt J 2022-8-9

在 MATLAB Online 中打开

First, crop the black corders from your image fiels. Then, use ellipticalFit() from,

https://www.mathworks.com/matlabcentral/fileexchange/87584-object-oriented-tools-for-fitting-conics-and-quadrics

getEgg=@(file) imbinarize(im2gray(imread(file)));
[Y1,X1]=find(edge(getEgg('egg1.png')));
[Y2,X2]=find(edge(getEgg('egg2.png')));
fobj1=ellipticalFit([X1(:),Y1(:)]');
fobj2=ellipticalFit([X2(:),Y2(:)]');
rotation = fobj2.angle-fobj1.angle

rotation =

137.9371

function out=getEgg(file)
out=imbinarize(im2gray(imread(file)));
end

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Matt J 2022-8-9

编辑：Matt J 2022-8-9

Yes, it can. But be sure to clean the boundaries of the image box.

Ashfaq Ahmed 2022-8-9

This code works perfectly! Thank you so much!!

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Answer 3

Matt J 2022-8-9

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1776600-how-to-calculate-the-rotation-of-this-egg#answer_1023940

在 MATLAB Online 中打开

BW1=~getEgg('egg1.png');
BW2=~getEgg('egg2.png');
S1=regionprops(BW1,'Orientation');
S2=regionprops(BW2,'Orientation');
rotation = S2.Orientation-S1.Orientation
rotation = -137.9439
function out=getEgg(file)
out=imbinarize(im2gray(imread(file)));
end