[Doug Tyler]

I'm trying to write a probe routine that will check a diameter. I don't have a problem, getting the x & y values. I don't know the mathmatical formula to get the diameter. The routine will measure 4 or more equally spaced points on the diameter, up to say 30 points. I want to be able to calculate the average diameter, and the maximum and minimum diameter. Any suggestions?

[Kiwi]

This will give you the centre XY and diameter from any three points.

X1 = ?:X2 =?:X3 = ?:Y1 =?:Y2 = ?:Y3 = ?
Ma = (Y2 - Y1) / (X2 - X1)
Mb = (Y3 - Y2) / (X3 - X2)
X = ((Ma * Mb) * (Y1 - Y3) + (Mb * (X1 + X2)) - (Ma * (X2 + X3))) / (2 * (Mb - Ma))
Y = -(1 / Ma) * (X - (X1 + X2) / 2) + (Y1 + Y2) / 2
Diameter = (Sqr((X2 - X) ^ 2 + (Y2 - Y) ^ 2))*2