having difficulties finding the radius of the circle

Question

http://imageshack.us/photo/my-images/189/unledgev.png/

i h'v having problem with finding the radius of this circle. i converted the original image in to gray scale and performed a edge detection operation. i used the Aforge.net API to apply circuler Hough transform to this edge image. but prior applying the Hough transform i need to give the circle radius that i want to find. the problem is i need need to find the circle radius or diameter in the vehicle's wheel. any one got any ideas?

private void Hough(Bitmap xx)
{
    HoughCircleTransformation circleTransform = new HoughCircleTransformation(35);
    // apply Hough circle transform
    circleTransform.ProcessImage(xx);

 }

Answer 1

You need a three-dimensional Hough space for that, parameterized by center-x, center-y and circle radius. Then your most likely position and radius is given as the maximum in the 3D Hough space. I'm afraid this is outside of ImageJ's capabilities, but it should be pretty easy to write up code by hand.