Least square circle calculation on a series of data points

[whale3]

I am taking a series of (x,y) part measurements that describe a circle  (radius & rotation angle). The center of the part and center of rotation are offset. Looking for code to do a least square circle calculation on this data set so diameter and out-of-roundness can be estimated. Platform LabView 8.2.

[MikeS81]

Hi whale3,

are x and y the radius and rotation angle or are this real points?

Mike

[RavensFan]

There was a recent message thread on the same topic, only in that case it was about X, Y pairs rather than R, theta pairs.  But the coordinate translation should be easy enough.

http://forums.ni.com/ni/board/message?board.id=170&view=by_date_ascending&message.id=307606#M307606

[whale3]

Thanks for responding to my inquiry, Mike.The equipment has an encoder to divide one revolution of the part into as many as 1024 segments. The radius is obtained by taking a reading with a measurement probe on the part, and doing a little math. Up to this point I have been counting encoder pulses, which would represent an angle to corespond to a measurement.

[whale3]

Thanks, Ravens Fan. Downloaded all of the circle fit VI's to look over and digest, but this looks like essentially what I want to do. Should be easy enough to convert my data (I tried doing this first with a cosine factoring program in a PLC!)

[altenbach]

Here is my simple solution from the above mentione thread:

(Is it not exaclty "least squares" in the classical sense but the sphere fit works typically very well..)

[whale3]

Thanks, altenbach. What I need is just a good fit which I can compare to a master part, scale, and use to check production parts. I've only done LabView for a few years, but many of the solutions to sticky problems I've had have come from people like you and your compatriots who are willing to help others (and love problem solving, too!). Thanks Again.