Calculating radius of circle

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Robert Smith
Robert Smith 2017-9-6
回答： Image Analyst 2017-9-8
Looking for a simple function. I would like calculate radius of a circle using three points. anyone done this before or know a function that will do this?
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Jacob Ward
Jacob Ward 2017-9-6
What do you mean by three points? Will these points be along the circumference of the circle? Will one be the center of the circle?

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回答（2 个）

Jacob Ward
Jacob Ward 2017-9-6
编辑：Jacob Ward 2017-9-8
Using the following equation:
You have three unknowns: h, k, and r.
So you'll need to solve a system of three equations using your three different x-y pairs:
(x1 - h)^2 + (y1 - k)^2 = r^2
(x2 - h)^2 + (y2 - k)^2 = r^2
(x3 - h)^2 + (y3 - k)^2 = r^2
Solving this system of equations will give you r and MATLAB's solve(eqns,vars) command should do the trick.
Something like this:
syms h k r
eqns = [(x1-h)^2+(y1-k)^2==r^2,(x2-h)^2+(y2-k)^2==r^2,(x3-h)^2+(y3-k)^2==r^2];
S = solve(eqns, [h k r]);
radius = S.r(2);
The S.r(2) takes the second r solution because the first one is the negative of what you want, the second is the positive and desired solution.
Image Analyst
Image Analyst 2017-9-8

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