Selecting data within a particular shape from a matrix.

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waqas
waqas 2019-8-31
评论： Matt J 2020-7-22
Hi,
I want to select data around point [169,547] in the attached v variable. Attached is the figure of the shape in which I want the coordinate values, their distance and angle with respect to the center point [169,547]. The case represents a dynamic crack which moves forward in the next frame and thus the center position will change in the next frame and the whole process will be repeated again. Any guidance regarding the implementation would be great.
Cheers
Waqas
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Image Analyst
Image Analyst 2019-8-31
His coordinate is probably (x, y) not (row, column), so the matrix should exist at row 169, column 547 in a matrix of 304 rows and 640 columns.
Matt J
Matt J 2020-7-22
waqas commented:
Hi,
I started a new question which is on the same lines as this question. It would be interesting to hear from you guys about that! I tried to figure it out by my own but am unable to get exactly what I want to.

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Matt J
Matt J 2019-8-31
编辑：Matt J 2019-8-31
As an example,
xc=547; yc=169; %center coordinates
rint=10; rext=50; %internal and external radii
[X,Y]=meshgrid((1:size(v,2))-xc, (1:size(v,1))-yc );
crack= Y<=rint & Y>=-rint & X<=sqrt(rint^2-Y.^2);
region= X.^2+Y.^2<=rext^2 & ~crack;
selected_data = v(region);
imshow(region);
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Matt J
Matt J 2019-10-7
编辑：Matt J 2019-10-7
If you know the inclineAngle, it should be a 2-line modification,
[X,Y]=meshgrid((1:size(v,2))-xc, (1:size(v,1))-yc );
[Theta,Rho]=cart2pol(X,Y);
[X,Y]=pol2cart(Theta+inclineAngle, Rho);
crack= Y<=rint & Y>=-rint & X<=sqrt(rint^2-Y.^2);
region= X.^2+Y.^2<=rext^2 & ~crack;
selected_data = v(region);
imshow(region);
waqas
waqas 2019-10-7
编辑：waqas 2019-10-7
Thank you so much for your input. It works perfectly. Just one correction, change the position of rho and theta in both cart2pol and pol2cart just in case someone comes across same problem in future.
Cheers,

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