# How to crop a square that has a rotational angle?

21 views (last 30 days)
Guilherme Pelegrini on 9 Mar 2017
Commented: Selina on 1 Apr 2019
I need to crop one square of this image:
As you can see, I can't use imcrop() because it isn't horizontal, the squares has a rotational angle, and the region cropped need to be precisely on the edge of the line.
How can I do it?

Massimo Zanetti on 9 Mar 2017
Edited: Massimo Zanetti on 9 Mar 2017
Inspect this: roipoly
Here is an example of what you can do:
%open an image
%run roi tool, where you can define your polygon
BW = roipoly(A);
%extract image pixels in the roi
S = regionprops(BW,'ConvexImage','BoundingBox');
r = S.BoundingBox;
Q = A( round(r(2)) + (1:r(4)) , round(r(1)) + (1:r(3)) );
%display cropped image
im = imagesc(Q);
axis image; colormap gray;
In the roipoly window track your points manually to define a polygon, as in the picture:
Selina on 1 Apr 2019
Hi,
Is it possible to use rectangle crop using the ROI function? If so, can anyone please send a sample coding?