How to scan a circle that is drawn over an image object?

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Zara Khan
Zara Khan 2018-7-14
评论： Zara Khan 2018-7-15
A circle is drawn over a binary image object using plot. After this drawn I again want to scan this circle and want to store its circumference coordinates points to an array. How to do that?
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Walter Roberson
Walter Roberson 2018-7-14
编辑：Walter Roberson 2018-7-14
Quantize the coordinates to integers, and take the unique pairs. No drawing required. If you need them in order, you can use boundary() or you can subtract the centroid so that the points circle the centroid, and then convert to polar coordinates, and sort by angle.
Zara Khan
Zara Khan 2018-7-14
编辑：Zara Khan 2018-7-14
I have got my unique points and this is forming a straight line . I am not getting any circle. How to resolve this ?

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Image Analyst
Image Analyst 2018-7-14
The form or size of the image below doesn't matter. It could be binary (with various irregularly shaped blobs in it), RGB, gray scale, whatever - it just doesn't matter.
Since you already have your (x,y) points of the "circle" (because you plotted them), if they're not already your circumference points (like it's a wiggly circle instead of a perfect circle), then you can fit a circle to what you have to get the "perfect" circle radius and center using the FAQ: https://matlab.wikia.com/wiki/FAQ#How_can_I_fit_a_circle_to_a_set_of_XY_data.3F
Now once you have the perfect circle, you can regenerate the perfect circle coordinates. Call round() on them if you want to quantize them to integer row, column values.
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Image Analyst
Image Analyst 2018-7-14
The just call poly2mask() with your x,y coordinates, and get an image, then just call bwboundaries() on that image. Done. Simple.

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