Howdy,
If the image you posted is the only type of image you are interested in....(let's assume that for the moment).
You would need to seperate the particle in the image from the background. (thresholding would do...)
Now you have pixels which are part of the particle and pixels which are not.
If the particle you are interested in is the partial circle...then you might use the find circles or the find circular edge function to find the center and radius estimate of the circle...
There is a find concentric edge function which would yield an array of coordinates lying along the lines where the pie shaped piece is cut out. there is a fit line to points function, and a find intersection of lines which would produce a good center of the circle. Then you would have to find the intersection of the lines previously found and the radius of the best fit circle...Not sure how to do that. (perhaps there is a solution for line and circle intersections in the math sections....)If you are not trying to find the edges of the picture you posted, but any shape...finding an edge and then taking a derivitive might work looking for inflection points. But I'm not sure how to do that either. Hope that helps.
