Finding circles in circles
Linus Nilsson from Sweden  [1 posts]
14 years

I have an application where I want to locate a circle within another circle, and get the center offset.

I have managed to get a really good image using Blob, Canny and Connect points, but when I use the Detect circles function it only finds one of the circles - not both.

As you can se in the picture there are two circles, but only one of them is found. If I increase the minimum radius above 91, the outer circle is found. Is it possible to find both circles at the same time?
Anonymous 14 years

Not just using the circle module but you can with others. Try this

1. Detect one circle and only display the graphic without the actual source data
2. Enlarge the detected circle using dialate or max or blur module
3. Take the negative of that image
4. Using the math module AND that image with the double circle one ... this should remove the detected circle and leave the other one alone.
5. Now you can detect circles again to find the second one.

If you provide the source image we can create this sequence to help you out if it does not make much sense. Basically you are zeroing out the first circle such that a second detection would only have one circle to find ... not an ideal solution but it should work.


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